Diffraction. When does it really matter with LF?

[AdamD]

Hi.
I'm not 100% sure this is the right spot for this question, so please feel free to move this. It's a technique thing....

Anyway, when looking at moden digital gear, I believe the generally accepted "fact" is that diffraction starts to creep in at about f/16. For those egale-eyed folks that might be true, but for me, not so much...I can say I see a general softening of the image (again digital here) at about f/22 or so.

I can't say the same for my one and only LF lens which is a Fuji 150mm f/5.6. to me it's super sharp at f/22 and I'm not even sure if there's a problem at f/32.

So, what's the deal here?

Do LF lenses tend to preform well at very small apertures, way better than modern digital gear? Is that just how it is, physics?

Or is diffraction just as prevelent in LF even at f/22 and I just need better glasses and eagle-eye training?

Thoughts??

Thx!!

[Luis-F-S]

Only you can choose between slight diffraction and lack of depth of field. Me? I'll take diffraction!

[Bob Salomon]

Hi.
I'm not 100% sure this is the right spot for this question, so please feel free to move this. It's a technique thing....

Anyway, when looking at moden digital gear, I believe the generally accepted "fact" is that diffraction starts to creep in at about f/16. For those egale-eyed folks that might be true, but for me, not so much...I can say I see a general softening of the image (again digital here) at about f/22 or so.

I can't say the same for my one and only LF lens which is a Fuji 150mm f/5.6. to me it's super sharp at f/22 and I'm not even sure if there's a problem at f/32.

So, what's the deal here?

Do LF lenses tend to preform well at very small apertures, way better than modern digital gear? Is that just how it is, physics?

Or is diffraction just as prevelent in LF even at f/22 and I just need better glasses and eagle-eye training?

Thoughts??

Thx!!

The smaller the format the sooner diffraction creeps in. The vast majority of modern lenses for 45 are diffraction limited at f22.
Modern digital lenses around 11or 16.

[Dan Fromm]

The rule of thumb is that resolution measured in line pairs/mm is limited by diffraction to 1500/f number. At f/1, the limit is 1500 lp/mm. At f/22 the limit is 68 lp/mm. And so on.

Another rule of thumb is that a print in which 8 lp/mm is resolved will look sharp at normal viewing distance. This has implications for how much a negative can be enlarged.

No enlargement (= contact printing) means that a negative shot at f/187 will appear sharp. Enlarging by 10x means that a negative shot at f/19 or so will look sharp. This is why my 35mm Kodachromes (ISO 25) of flowers shot at 1:1 and f/16 nominal, f/32 effective, look fuzzy when printed 8x10.

The diffraction limit rule of thumb I gave above is a bit lenient. It gives resolution at 0% contrast, resolution with useful contrast is somewhat lower than the rule of thumb suggests.

[Bruce Watson]

So, what's the deal here?

...

Thoughts?

Everything in LF is a trade off. If you open up too far you have shallow DOF. If you stop down too far you soften the image through diffraction. Etc. The bottom line as you'll find eventually, is to artfully walk all the trade offs.

What many people have learned before us is that while diffraction limiting makes the entire image slightly softer, DOF works more like a gradient -- sharpness varies across the image. We see the variation in sharpness fairly easily since our visual systems are excellent with patterns.

This is at least partly why the pioneers like Weston, Adams, Cunningham, etc. who founded Group f.64 chose that name. They valued over all focus. That is, they were willing to give up a little entire image softness to get more entire image DOF.

How you personally feel about it is of course easy to test -- all you need do is make a number of identical exposures using different f-stops. Make prints from each, put them up on your "viewing wall" side by side and see what you think. The more enlargement of course, the easier it is to see, which of course points you to another consideration. And there are many more considerations out there. :cool:

[Bob Salomon]

Everything in LF is a trade off. If you open up too far you have shallow DOF. If you stop down too far you soften the image through diffraction. Etc. The bottom line as you'll find eventually, is to artfully walk all the trade offs.

What many people have learned before us is that while diffraction limiting makes the entire image slightly softer, DOF works more like a gradient -- sharpness varies across the image. We see the variation in sharpness fairly easily since our visual systems are excellent with patterns.

This is at least partly why the pioneers like Weston, Adams, Cunningham, etc. who founded Group f.64 chose that name. They valued over all focus. That is, they were willing to give up a little entire image softness to get more entire image DOF.

How you personally feel about it is of course easy to test -- all you need do is make a number of identical exposures using different f-stops. Make prints from each, put them up on your "viewing wall" side by side and see what you think. The more enlargement of course, the easier it is to see, which of course points you to another consideration. And there are many more considerations out there. :cool:

And focused at different points, 1/3rd into the scene, ½ into the scene, on the nearest point wanted sharp, on the furthest point you want sharp.
And decide how large you will print the scene since dof also varies with magnification.

[Neal Chaves]

And all of this assumes a lens with a very, very flat field, something not really suitable for general photography. Dagors, for example, were kown for having a "doughnut-shaped" field if not stopped down sufficiently.

[Mark Sawyer]

No enlargement (= contact printing) means that a negative shot at f/187 will appear sharp. Enlarging by 10x means that a negative shot at f/19 or so will look sharp.

For large format, this is key. If you're contact printing, (no enlargement of the negative), forget diffraction. It will barely show up at f/256.


This is why my 35mm Kodachromes (ISO 25) of flowers shot at 1:1 and f/16 nominal, f/22 effective, look fuzzy when printed 8x10.


Nitpicking, but isn't 1:1 and f/16 nominal really f/32 effective?

[Dan Fromm]

For large format, this is key. If you're contact printing, (no enlargement of the negative), forget diffraction. It will barely show up at f/256.



Nitpicking, but isn't 1:1 and f/16 nominal really f/32 effective?

You're right. Stupid typo, corrected. Thanks for spotting it and telling me.

[Jim Jones]

There are many rules for optimum apertures, but my favorite is: stop down until the iris appears to be about 1/4 inch in diameter when viewed through the front lens cell. This applies equally well to all film sizes. Some subjects, some lighting conditions, some personal preferences, and all practical pinhole photography demand exceptions.

[Mark Sawyer]

Jim's post reminds me of a little trick I learned from ancient markings on a couple of my old shutters: put little paint/pencil marks on the aperture scale at 1 inch and 1 centimeter. It makes the bellows extension math incredibly simple. 30 cm extension at 1 cm aperture? f/30. 45cm extension at the same aperture? f/45.

For a smaller apertures, a mark for .5 cm is almost as simple.

[cowanw]

For large format, this is key. If you're contact printing, (no enlargement of the negative), forget diffraction. It will barely show up at f/256.



Nitpicking, but isn't 1:1 and f/16 nominal really f/32 effective?
They are from a light exposure point of view, because light obeys the inverse square law , but does that mean that diffraction, which does not rely on the inverse square law, is the same at 1:1 and f/16 is the same as infinity and f/32. My gut tells me not.

[Doremus Scudder]

For me, depth of field trumps diffraction degradation every time.

I shoot 4x5. If I have to stop down a lot, I just reduce the maximum enlargement size I can get from that particular negative. Printing 8x10 from 4x5 film, I can stop way down, even to f/64, and not get objectionable diffraction degradation.

Also, it seems that scenes that need a lot of stopping down are the ones I don't want to enlarge much anyway; things like close-up still lifes, natural details, etc.

One of the big advantages of large format is that one can use movements to optimally position the plane of sharp focus in a scene and thereby be able to use a smaller aperture than one would need without movements to get everything acceptably sharp. Mastering view-camera technique is a real help.

Best,

Doremus

[Dan Fromm]

They are from a light exposure point of view, because light obeys the inverse square law , but does that mean that diffraction, which does not rely on the inverse square law, is the same at 1:1 and f/16 is the same as infinity and f/32. My gut tells me not.

Bryan, your gut is mistaken. See, for example, H. Lou Gibson's Close-Up Photography and Photomacrography, EKCo publication #N-16.

[cowanw]

The nearest library copy is the centre of Canada, that is Toronto. One day I will get there:)

[Dan Fromm]

The nearest library copy is the centre of Canada, that is Toronto. One day I will get there:)Inexpensive at on-line used book stores.

[Greg]

In the late 1970s and early 1980s I shot a lot of waterfalls in New England with my 8x10 and a 12" Wollensak Velostigmat Series II. All exposures shot at f/64 or f/90. At the time I made contact prints on Varigram or Varilour FB paper. Around 10 years ago scanned the negatives and made digital negatives to print Platinum/Palladium prints from. Loss of sharpness from diffraction is definitely in the original 8x10 negatives if you look at them under a low power X4 Loupe. Holding the prints side by side at arm's length, most people would say, resolution wise, that the FB prints are a tad bit sharper than the Platinum/Palladium prints. Aesthetically and tonality wise, the Platinum/Palladium prints far outshine the FB prints. Several of my friends/relatives are not photographers and when asked which print is sharper, all responded that the Platinum/Palladium print was definitely sharper. When I am doing Photomicrography or Photomacrography diffraction, to me, is a major concern and factor. When I am shooting outside with my 8x10 or 11x14, diffraction matters little to me. The image matters all to me. If I were concerned with loss of sharpness from diffraction, I just might never take out my 8x10 and 11x14 ultraWA pinhole cameras. To me the final image in the final print is what matters the most...
Comments most welcome

[Dan Fromm]

Re Greg's post #17 above, +1. Sharpness is overrated.

[Drew Wiley]

From my own practical needs, I try not to go smaller than f/32 for 4x5 format, or smaller than f/64 with 8X10 film (or smaller than f/45 if a large print like 30X40 inch is in mind). Obviously, I'm referring to enlargements; I rarely contact print.

[AdamD]

Hi all,

Good thread...thank you.

So, I've re-read the thread and here's what I was able to get out of it....

- There are rules of thumb to determine diffraction
- There are generalities that guide users with how to avoid diffraction
- There a school of thought that goes something like this...'so what, just shoot more'
- There a school of thought that understands the compromises involved in photography so pick the one that most important to you at the time of the shot
- Large format affords the user unparalleled flexibility to minimize diffraction, take advantage of it

Pretty good, I can roll with that.

Thanks!!
Adam

[Drew Wiley]

Good assessment, Adam. But to the above options, you could also add that diffraction is just another potential tool, to either employ or set aside according to the specific goal in mind, with critical sharpness being the opposite tool. Some like to use a broad paintbrush, others a fine narrow one. Or the whole depth of field problem might force your hand : ULF shooters generally contact print, yet often need very small apertures anyway due to serious depth of field issues.

[Bernice Loui]

Goes back to what the image-maker's print goals are..

IMO group f64 held a significant influence on many LF image creators. This was the ideology-belief everything in the print image to be ~sharp~. There was no question this greatly influence my own print LF image making goals. That was circa early 1980's. That was a time when few images were made with apertures larger than f16, most were f22 to f45 as needed. Going up in film format size made the taking apertures smaller, typically f32 to f45 and at time may be a tad smaller.. This was driven by a list of factors from camera alignment precision, film flatness, the ideology of everything in the image in focus being the primary goal.

~Except, LF was not the only fit format being used for image making.

There was 35mm, 120, video image making cameras used. Add to this films made by folks like Stanley Kubrick, Alfred Hitchcock, Steven Spielberg, Ken Burns and many others.. they nice illustrated the visual effectiveness and emotional expressive power of selective focus and the value of lens out of focus rendition.

Add to this, the entire world of Soft Focus or "sort-of-focus" lenses that are most effective on sheet film formats 5x7 and larger.

Since those early days of LF image making, the method today is to stop the everything in the image required to be in apparent focus.
It has since evolved to what is the expressive value of holding specific items in the image in focus, what would result in a more expressive and effective image if specific areas in the print are rolled out of focus. Knowing this along with the very real effects of diffraction and the power of view camera movements to control what is in focus -vs- what cannot be held within the plane of focus (yes it curves as camera movement is applied) delivers LOTs of options as to using what is in or out of focus as a tool for expressive image making.

Over time, the lens choices reflect this methodology..

APO process lenses or Dagor lenses are preferred for everything in apparent focus images. This means a taking aperture of f16 to f45. For images that are selective focus or controlled rolling out of focus lens choice becomes Tessar.

Camera movements and what they can do greatly influences taking aperture. The drill is to figure out what the print image needs and should be.
In the case of everything in the image to be in apparent focus, camera movement is applied as needed to achieve this with the largest possible taking aperture. There is no reason to close down the aperture more than absolutely needed. This demands fit to be flat in the film holder, camera to hold and be precise between front to rear standards with camera movements being precise, accurate and stable. This is how to avoid diffraction and extracting what is possible with a view camera to meet a print image goal.

Example (previously posted). Image of this building was made with a 8-1/2" f6.3 Kodak Commercial Ektar. Taking aperture is f11, 5x7 film format, Sinar C camera. Camera movements were applied as needed with the lens at f6.3, then stopped down just enough to bring the image areas that must be in focus, into apparent focus. Flat do not believe in closing down the aperture down more than needed.
210123

Keep in mind lens focuses on a plane, as the aperture is closed down, image rendered becomes apparent focus unless the image being recorded is with the lens set to true infinity. In this case, large lens apertures can be applied effectively for a given lens design and camera's ability to hold alignment, precision, and film absolutely flat.

Then there is the obsession with "sharpness". There are many aspects to what sheet film can offer that is far beyond "sharpness".

BTW, if contact prints are made, stopping down past f64 is often not an issue or problem. Or why 8x10 or larger film sizes can make really GOOD contact prints.



Bernice

[Vaughn]

Re Greg's post #17 above, +1. Sharpness is overrated.

Agreed. Just another tool -- use wisely.

[LabRat]

If you really want to get this out of your system, I have applied modern tech to help evaluate what your lenses are doing...

I now use my large 4X5 studio camera as a optical bench by using a DSLR mounted on a pine plank that fits in the Graflok back holder with a plumbing extension for holding a Nikon F (or other) lens mount so the camera can ride the back... (Or buy an adapter for not too much...) Then you can analyze different areas of the focal plane (by using camera shifts) and directly observe different areas in real time...

For instance, you can check your lens at all the aperture settings, where you can notice it might be mushy at its extremes, like wide open, but when you stop down a stop or two, the image "firms" up, or at the other end of the scale, f22 might be good but image mushes out below that somewhere... And there are other tests like color saturation, overall contrast, edge sharpness, color fringing etc... But this tends to test the lens, but not overall response of the entire film/printing system... But you start getting an idea of the tonality range...

You can sort lenses into different "types" of contrast/resolution that can combine into different film effects, like soft or harder contrast, overall softer or harder sharpness, lower or higher general key etc and start doing film tests of the lenses of how they render on film... Generally, you will be looking at the scale across film range to look for the "look" the paticular lens will render in the scene and with materials etc... And armed with testing, you make better choices to decide the "look" you want...

Steve K

[Mark Sawyer]

Why isn't diffraction considered an optical aberration? It's missing from the conventional list of aberrations.

Late night pondering... :confused:

[Vaughn]

It's missing from the conventional list of aberrations? That itself might be an aberration.

[Dan Fromm]

Why isn't diffraction considered an optical aberration? It's missing from the conventional list of aberrations.

Late night pondering... :confused:

Well, it can't be corrected.

[Bernice Loui]

Caution on this, Digital image sensors have a substantial stack of filter in front of the silicon sensor array. This is done to limit IR, separate color and more.. Film does not have this stack of filters which can add a variable to image produced on film -vs- digital image sensor.


Bernice



If you really want to get this out of your system, I have applied modern tech to help evaluate what your lenses are doing...

I now use my large 4X5 studio camera as a optical bench by using a DSLR mounted on a pine plank that fits in the Graflok back holder with a plumbing extension for holding a Nikon F (or other) lens mount so the camera can ride the back... (Or buy an adapter for not too much...) Then you can analyze different areas of the focal plane (by using camera shifts) and directly observe different areas in real time...

For instance, you can check your lens at all the aperture settings, where you can notice it might be mushy at its extremes, like wide open, but when you stop down a stop or two, the image "firms" up, or at the other end of the scale, f22 might be good but image mushes out below that somewhere... And there are other tests like color saturation, overall contrast, edge sharpness, color fringing etc... But this tends to test the lens, but not overall response of the entire film/printing system... But you start getting an idea of the tonality range...

You can sort lenses into different "types" of contrast/resolution that can combine into different film effects, like soft or harder contrast, overall softer or harder sharpness, lower or higher general key etc and start doing film tests of the lenses of how they render on film... Generally, you will be looking at the scale across film range to look for the "look" the paticular lens will render in the scene and with materials etc... And armed with testing, you make better choices to decide the "look" you want...

Steve K

[Drew Wiley]

Mark - Diffraction affects different wavelengths differently. I discovered this long ago in reference to the setting sun over sharp ridges where there is extremely clean air, first at Comb Ridge in Utah, then in Kauai. At first I blamed my highly-corrected new lens for the color fringing, but then saw it with my own eyes. The rays were truly bent differently over sharp geological edges in the distance. Something analogous happens with very small apertures, especially in high-magnification optical microscopy. There are very expensive sophisticated methods for correcting this. The primary wavelengths are completely separated, then more precisely re-aligned through electronically controlled magnetic mirrors - add about another $40,000, plus digital output afterwards. There might be similar technology in the latest astronomical equipment - add 400 million dollars, I'd imagine.

[MAubrey]

In the late 1970s and early 1980s I shot a lot of waterfalls in New England with my 8x10 and a 12" Wollensak Velostigmat Series II. All exposures shot at f/64 or f/90. At the time I made contact prints on Varigram or Varilour FB paper. Around 10 years ago scanned the negatives and made digital negatives to print Platinum/Palladium prints from. Loss of sharpness from diffraction is definitely in the original 8x10 negatives if you look at them under a low power X4 Loupe. Holding the prints side by side at arm's length, most people would say, resolution wise, that the FB prints are a tad bit sharper than the Platinum/Palladium prints. Aesthetically and tonality wise, the Platinum/Palladium prints far outshine the FB prints. Several of my friends/relatives are not photographers and when asked which print is sharper, all responded that the Platinum/Palladium print was definitely sharper. When I am doing Photomicrography or Photomacrography diffraction, to me, is a major concern and factor. When I am shooting outside with my 8x10 or 11x14, diffraction matters little to me. The image matters all to me. If I were concerned with loss of sharpness from diffraction, I just might never take out my 8x10 and 11x14 ultraWA pinhole cameras. To me the final image in the final print is what matters the most...
Comments most welcome

This is a good example of how contrast affects apparent sharpness in ways that matter more than actual resolution.

Reminds of me of this essay on sharpness and pinholes and deciding what size is best for your use case:
The Pinhole Camera Revisited (https://www.kth.se/social/files/5c7fae6756be5bc7488edcb5/Pinhole camera.pdf)

[Bernice Loui]

High contrast images often gives the visual impression of "sharper" when the perceived sharpness is not real. This has been discussed many times previously on LFF.

One of the advantages that comes from larger sized sheet film is the ability to hold subtle contrast renditions that can be difficult to impossible on smaller film formats.. this has ZERO to do with image sharpness or resolution. It is why soft focus lenses used on 8x10 film and larger then contact printed have rather special image qualities that cannot be achieved any other way.

Possible image resolution aka "sharpness" with smaller film format is difficult to achieve making this a goal to achieve? While sheet film often gains image resolution by brute-force film recording area rendering the many other aspects of print image quality far more significant than simple sharpness.. which could be a residual obsession from those beginning LF endeavoring into LF sheet film?

Diffraction effects can be reduced by limiting the light used to create the image to a shorter wave length, as in blue light can theoretically produce a higher resolution image than red light with the same lens aperture. Much a matter of smaller can fit more in then out of a fixed sized area.



Bernice

[Ulophot]

At the risk of redundancy, I'll sing my note about portraiture, as an illustration of principle.

Others have noted that the final result, or look, you desire to achieve, is determining. Not every portraitist desires tack-sharp images or will print poster-size, and I am one. I don't really want a super-apochromat ultra-sharp lens for my work (though I admit to having been through my share of if-only-I-had syndrome), and frankly, my 210 Komura and 135 Nikkor (which latter some have called the dog of the line) leave me nothing to complain of. Though I have come to LF for the essentially invisible grain among other features, I shoot fast film in both 4x5 and 645. At 11x14, even with cropping, if I have done my job well, the content of the image will convey itself past all but those who really aren't looking at the portrait but at the rendering of insignificant detail. I have done it myself, so I make no judgement, but like to remember Adams's dictum, variously stated, that nothing is more pointless than a sharp image of a fuzzy concept.

I had posted a question similar to yours in the forum a while back and got some good advice about diffraction and sharpness-optimization at various distances with my lenses. I made some tests. For my work, the issue is now behind me, as for a number of others posting here. (You might take a look at Doremus's beautiful work on his website, among many others.)

[Mark Sawyer]

Well, it can't be corrected.

Diffraction can be corrected by opening up the aperture. Just like you can correct spherical aberration or curved field by closing down the aperture.

But one can also correct spherical aberration or curved field by altering lens design, which doesn't work for diffraction. So maybe.

Just curious...

[Drew Wiley]

That's not correcting diffraction, just reducing or avoiding it. If you need a small aperture, you need a small aperture, and diffraction comes with the territory.

[Mark Sawyer]

Agreed, Drew, but which other aberrations are ever corrected to perfection, not just reduced or avoided?

[Drew Wiley]

For all practical purposes, most modern large format lenses are very well corrected relative to typical applications. It's a tougher climb trying to squeeze the same amount blood out of tiny cherry tomatoes. I feel the pinch whenever I mix MF prints into the same portfolios as LF prints; and that's where being nitpicky about lenses really counts.
I've seen sample photos from classified cameras that were almost unbelievably well-corrected; but even if I could afford a hundred thousand dollar lens and a two hundred pound camera, it wouldn't improve my own work one bit. The most important lens set ever made is your own pair of eyes.

[Bernice Loui]

The most important item in the print making process is the Artist-Photographer. All that ~hardware~ stuff are mere tools as a means to accomplish an Artistic expression via images.

A very crude and not the best analogy for diffraction would be the volume of beans that can be passed in then out of a fixed dimension opening with the volume of beans used to create an image. If the dimension of the opening these beans are going in then out of is reduced, the volume of beans used to create an image is reduced. At some point if the opening is made smaller than the individual bean, the flow of beans stops or no image can be created with the beans.


Bernice

[Mark Sawyer]

A very crude and not the best analogy for diffraction would be the volume of beans that can be passed in then out of a fixed dimension opening with the volume of beans used to create an image. If the dimension of the opening these beans are going in then out of is reduced, the volume of beans used to create an image is reduced. At some point if the opening is made smaller than the individual bean, the flow of beans stops or no image can be created with the beans.

In our case, that would be an opening in the photon-wave-amplitude size, something well below f/64 for our lenses.

One thing I don't understand about diffraction is why it is affected by focal length. It seems that it should be an effect of photon ray and raw aperture size. This is me not getting it, but why would diffraction be more on a 1000mm lens at f/100 than on a 100mm lens at f/10? Disregarding the power of the front element, they'd both have the same aperture size. I tried to figure it out from the Fraunhofer diffraction equation variations, but it just made my head hurt... :confused::confused::confused:

[Dan Fromm]

But it isn't affected by focal length. Effective aperture, a dimensionless number, is what matters.

[Vaughn]

The most important item in the print making process is the Artist-Photographer. All that ~hardware~ stuff are mere tools as a means to accomplish an Artistic expression via images...Bernice

And the tools shape the artist as well as the art.

The rest of you post reminds me of the joke about the racket all the different body parts were making, arguing about who was the most important -- finally the small sphincter muscle quietly said "Quiet up there, or I'll clamp shut for a week." And peace prevailed again...

[Mark Sawyer]

But it isn't affected by focal length. Effective aperture, a dimensionless number, is what matters.

That makes sense. But the diffraction limits calculators I've seen go by f/stops, not actual aperture size. And of course, f/stop dimensions change with focal length, as that's the "f" in "f/stop".

[Dan Fromm]

focal length/entrance pupil is dimensionless.

[Kirk Gittings]

Only you can choose between slight diffraction and lack of depth of field. Me? I'll take diffraction!

I was giving a talk many years ago with Mark Citret, out in CA somewhere on architectural photography (Not commercial but more art/personal AP), maybe it was at the VC Conference in Carmel. We both repeatedly referred to the aperture in many of our 4x5 exposures as f/32. After the talk someone came up to us, somewhat aghast, saying that the diffraction would ruin our images as if at an aperture smaller than f/22 there was some cliff of unacceptable unsharpness you fell off of. Believe your experience. Try it out and see what works for you and your type of imagery.

I really like what Bruce said "Everything in LF is a trade off. If you open up too far you have shallow DOF. If you stop down too far you soften the image through diffraction. Etc.

The bottom line as you'll find eventually,
is to artfully walk all the trade offs."

nice.

[Drew Wiley]

Gosh. It's been a couple decades since I've bumped into to Mark. Some well-known 4x5 landscape photographers routinely use f/32 because it provides enough depth to generally make up for film sag or flatness issues in the holder, yet the amount of diffraction is still barely noticeable even in really big enlargements. Wide angle or shorter focal length lenses tend to be affected by diffraction a little sooner, but their images are also affected more by any lens to film distance deviation; so for all practical purposes, it's a wash. And it's too nonsensically complicated to figure out on the fly every hypothetically ideal this or that. If one is a scientific photographer and working with truly flat glass plates in a lab, that might be a different story.

[Serge S]

And the tools shape the artist as well as the art..

Yes!

"We shape our tools and thereafter our tools shape us."
Marshall McLuhan

[Alan Klein]

Gosh. It's been a couple decades since I've bumped into to Mark. Some well-known 4x5 landscape photographers routinely use f/32 because it provides enough depth to generally make up for film sag or flatness issues in the holder, yet the amount of diffraction is still barely noticeable even in really big enlargements. Wide angle or shorter focal length lenses tend to be affected by diffraction a little sooner, but their images are also affected more by any lens to film distance deviation; so for all practical purposes, it's a wash. And it's too nonsensically complicated to figure out on the fly every hypothetically ideal this or that. If one is a scientific photographer and working with truly flat glass plates in a lab, that might be a different story.

As you know I recently started shooting LF. Mainly I've been shooting medium format 6x7 landscape. My general practice with MF was to calculate the DOF range using the DOF scale on the lens or a handy chart. Then stop down one additional stop for good measure. I used to enlarge (commercially) to 16x20". If there was diffraction, I didn't notice probably because I didn't know what I'd be looking for. But everything was in focus most of the time that I wanted to be in focus.

So now that I've taken up LF I read that f22 is a good f stop to work with. Every shot I took this year has been at f22. Of course, with tilts, the whole formula I had been using with MF is probably thrown out the door. So how do people decide the best f stops on the fly. I know there are some special LF tables you can look up. But the whole process seems too arcane and I'm having enough trouble focusing and seeing things upside down to figure out a better stop other than f/22.

Anyone with simple suggestions?

[Bernice Loui]

Chronic f22 syndrome. Did this back in the mid 1980's at the beginning of learning how to use a view camera (4x5). This came about from reading about how view camera lenses were optimized at f22 (Rodenstock Sironar N, Schneider Super Angulon at that time). It was a struggle to learn how to view the upside down and backwards image on the dim (perception from that time) ground glass image. This brought about a variety of viewing aids from reflex viewers to fresnel lenses to different brands of ground glass. Struggled desperately with trying to figure out how camera movements work and what they did. By default, it was compose, focus best guess-possible, apply cameras movements with mixed confusion if it helped or made the image worst, stop the lens down to f22 or so and ... accept what happened.

At some point, the opportunity to use a Sinar P in studio happened with a VERY experienced photographer. This experience plus LOTs of Polaroid film and LOTs of film burned taught me the value of Polaroid proofing (Ha!) and the value of a camera with precision as a teaching tool. The other skill that must be learned and acquired is how to view the ground glass without viewing aids. This takes time to learn and develop. As eyes age, this compounds the problem. While there are times when trying to achieve every item in the image to be in apparent focus means stopping the lens down lots, there are often times when this is excessive. It is driven by items in the image and image composition and the ability-skill of the image maker to apply camera movements as needed to achieve overall focus. This does mean evaluating the image with the lens stopped down to taking aperture and camera movements (as needed, if used) applied. This is why the preference for no fresnel lens as the grooves work hard against this, a camera with precision of camera movements and stability, a 7x ground glass loupe with a GOOD dark cloth. Much of this is about blocking out ambient light then allowing your eyes to adjust to the available light on the GG.

Growing out of the chronic f22 habit can be a good thing.


Bernice




As you know I recently started shooting LF. Mainly I've been shooting medium format 6x7 landscape. My general practice with MF was to calculate the DOF range using the DOF scale on the lens or a handy chart. Then stop down one additional stop for good measure. I used to enlarge (commercially) to 16x20". If there was diffraction, I didn't notice probably because I didn't know what I'd be looking for. But everything was in focus most of the time that I wanted to be in focus.

So now that I've taken up LF I read that f22 is a good f stop to work with. Every shot I took this year has been at f22. Of course, with tilts, the whole formula I had been using with MF is probably thrown out the door. So how do people decide the best f stops on the fly. I know there are some special LF tables you can look up. But the whole process seems too arcane and I'm having enough trouble focusing and seeing things upside down to figure out a better stop other than f/22.

Anyone with simple suggestions?

[Vaughn]

I never thought of f22 as a magic number...now f64, that's a different beastie! Early on, my images usually required the DoF generated by f64 and I did not know about diffraction issues...ignorance was bliss.

Alan, you might benefit from some strong reading glasses -- ones that can get your face within a foot of the GG so you can study the entire image under the darkcloth. I remember the time I pulled my head out from underneath the darkcloth and for an instant, thought the rest of the world was upside down...neat. I started using a Rolleiflex, I guess since everything was backwards, I got use to everything being upside down with the 4x5 quickly.

[Alan Klein]

Chronic f22 syndrome. Did this back in the mid 1980's at the beginning of learning how to use a view camera (4x5). This came about from reading about how view camera lenses were optimized at f22 (Rodenstock Sironar N, Schneider Super Angulon at that time). It was a struggle to learn how to view the upside down and backwards image on the dim (perception from that time) ground glass image. This brought about a variety of viewing aids from reflex viewers to fresnel lenses to different brands of ground glass. Struggled desperately with trying to figure out how camera movements work and what they did. By default, it was compose, focus best guess-possible, apply cameras movements with mixed confusion if it helped or made the image worst, stop the lens down to f22 or so and ... accept what happened.

At some point, the opportunity to use a Sinar P in studio happened with a VERY experienced photographer. This experience plus LOTs of Polaroid film and LOTs of film burned taught me the value of Polaroid proofing (Ha!) and the value of a camera with precision as a teaching tool. The other skill that must be learned and acquired is how to view the ground glass without viewing aids. This takes time to learn and develop. As eyes age, this compounds the problem. While there are times when trying to achieve every item in the image to be in apparent focus means stopping the lens down lots, there are often times when this is excessive. It is driven by items in the image and image composition and the ability-skill of the image maker to apply camera movements as needed to achieve overall focus. This does mean evaluating the image with the lens stopped down to taking aperture and camera movements (as needed, if used) applied. This is why the preference for no fresnel lens as the grooves work hard against this, a camera with precision of camera movements and stability, a 7x ground glass loupe with a GOOD dark cloth. Much of this is about blocking out ambient light then allowing your eyes to adjust to the available light on the GG.

Growing out of the chronic f22 habit can be a good thing.


Bernice

Well it's nice that someone else suffered through the same things I'm suffering through now. At least I don't feel like a dope. :)

Maybe I'll remove the fresnel from my Chamonix 45H-1 if I can focus better and easier. How does a GG without the fresnel work better? How do you approach focusing without the fresnel vs. with it?

[Bob Salomon]

Well it's nice that someone else suffered through the same things I'm suffering through now. At least I don't feel like a dope. :)

Maybe I'll remove the fresnel from my Chamonix 45H-1 if I can focus better and easier. How does a GG without the fresnel work better? How do you approach focusing without the fresnel vs. with it?

It doesn’t. The fresnel does 2 things. One it evens the light spread across the gg diminishing the fall off across the gg and secondly it brightens the gg image.

[Alan Klein]

I never thought of f22 as a magic number...now f64, that's a different beastie! Early on, my images usually required the DoF generated by f64 and I did not know about diffraction issues...ignorance was bliss.

Alan, you might benefit from some strong reading glasses -- ones that can get your face within a foot of the GG so you can study the entire image under the darkcloth. I remember the time I pulled my head out from underneath the darkcloth and for an instant, thought the rest of the world was upside down...neat. I started using a Rolleiflex, I guess since everything was backwards, I got use to everything being upside down with the 4x5 quickly.

I tried the ones you buy from the drug store. But they aren't too good. I wear glasses with an astigmatism. The glasses are the graduated kind, I forget the actual name. The thing is I always used regular view on my medium format to nail the focus. I don;t know why a loupe should be necessary with 4x5? With MF I move the focus in and out until I see it's in focus. Why can't that be done with 4x5?

[Bernice Loui]

Medium format cameras often have some magnification built into the viewing system as a "pop-up"magnifier or magnification is built into a prism. The rubber eye cup works as an ambient light excluder (effectively a dark cloth on LF). In the world of LF, it is not possible to evaluate focus without a magnifier. Learning how to use a magnifier on the GG is one of the fundamental LF image making skills.


Bernice




The thing is I always used regular view on my medium format to nail the focus. I don;t know why a loupe should be necessary with 4x5? With MF I move the focus in and out until I see it's in focus. Why can't that be done with 4x5?

[Alan Klein]

It doesn’t. The fresnel does 2 things. One it evens the light spread across the gg diminishing the fall off across the gg and secondly it brightens the gg image.

Bob, the view looks OK with my 300mm. But for the 75mm or 90mm, the light falloff as you move away from the center is a lot anyway with the fresnel. I have to move my head all around anyway. Also, the focus for me is hard. Is that because of the fresnel? Would the tradeoff be better of less light but easier focus if I removed the fresnel? Sorry to have hijacked the thread. It seems my problems are beyond diffraction.

[Bob Salomon]

Bob, the view looks OK with my 300mm. But for the 75mm or 90mm, the light falloff as you move away from the center is a lot anyway with the fresnel. I have to move my head all around anyway. Also, the focus for me is hard. Is that because of the fresnel? Would the tradeoff be better of less light but easier focus if I removed the fresnel? Sorry to have hijacked the thread. It seems my problems are beyond diffraction.
Do you have a fresnel designed and sold for your camera or one of those stationary store fresnel sheets?

[Alan Klein]

Medium format cameras often have some magnification built into the viewing system as a "pop-up"magnifier or magnification is built into a prism. The rubber eye cup works as an ambient light excluder (effectively a dark cloth on LF). In the world of LF, it is not possible to evaluate focus without a magnifier. Learning how to use a magnifier on the GG is one of the fundamental LF image making skills.


Bernice

Some have suggested a magnifier eyeglasses, let's say around 4x. WOuld that work. It would free up my hands as an additional benefit as I need both hands to controls the two knobs required to focus my H-1?

[Alan Klein]

Do you have a fresnel designed and sold for your camera or one of those stationary store fresnel sheets?

Came with the Chamonix camera.

[Alan Klein]

MAybe it's not so good.

[Bob Salomon]

MAybe it's not so good.

Probably not. You might ask them.

[Daniel Unkefer]

Instead of a dark cloth and 7x magnifier, I am using fresnel lenses on my Plaubel Peco Profias, and Sinar Norma cameras. And I have Plaubel/Sinar monocular oculars, with bag bellows, on the back of each 4x5/5x7 camera. This works great in the studio and I can see fine enough detail most cases. On the back of the 8x10 Norma I have an 8x10 Bag Bellows and binocular Sinar Viewer. So far I am also happy with that. But several excellent loupes are available if I need to study the ground glass grain. If I need to remove the fresnels that isn't too difficult to do.

[Tin Can]

I have used Mamiya RB67 Chimney finder on 8x10 GG and up

I prefer my 9X loupe on a string around my neck

[Vaughn]

Some have suggested a magnifier eyeglasses, let's say around 4x. WOuld that work. It would free up my hands as an additional benefit as I need both hands to controls the two knobs required to focus my H-1?

I recommended the glasses not for focusing, but for being able to clearly see the whole 4x5 GG in focus while under the darkcloth for the purpose of composition. One generally can not compose with a loupe. Ask you eye doctor, bring in your camera if she or he does not understand your needs.

Yes, one has to move ones head around -- the brightest view is always to put your eye on the same path as the light coming in through the lens. Fresnels help a little but you don't get something for nothing. I don't like them.

[Michael R]

Alan, even if you get over “f/22 syndrome” you will probably end up at f/22 or smaller anyway.

[Drew Wiley]

If you're on the beach with your dog, you can play fresnel frisbee. That's about all they're good for as far as I'm concerned. Having the right kind of grind on your glass to begin with is way more important.

[Doremus Scudder]

... So how do people decide the best f stops on the fly. I know there are some special LF tables you can look up. But the whole process seems too arcane and I'm having enough trouble focusing and seeing things upside down to figure out a better stop other than f/22. Anyone with simple suggestions?

No "simplistic" suggestions, nope. But, the method of choosing an optimum f-stop based on focus spread, once mastered, is really, really simple in application. It takes me about five seconds to decide which f-stop is going to work best for any particular shot. It's not arcane in the least.

I seem to keep posting this link, but here it is again, from the LF home page and the article "How to select the f-stop."

https://www.largeformatphotography.info/fstop.html

Heck, if you're lazy or just want the down-and-dirty approach, you don't even have to read the whole article. Just figure out the basic method, print out the tables listed toward the end of the article and paste them on your camera and go to work.

A couple of observations: Most LF lenses work best at or close to f/22. So, there's very little reason to shoot at a larger aperture than that unless you want a shallow depth of field and need the larger aperture for that.

However, if you want lots of near and far things in your photographs to be in focus, there is a very good reason to stop down farther than f/22 when you need the depth of field, despite the slight fall off of performance caused by the (very gradual) onset of diffraction degradation.

You have to enlarge a 4x5 negative a lot to notice diffraction degradation from f/32. How many 30x36-inch prints do you make anyway? Heck, 11x14s from negatives made at f/45 exhibit little or no degradation due to diffraction unless you get out your loupe.

So, in practice, you'll be using a small range of apertures between f/22 and f/45, depending on the focus spread. For those scenes that require stopping down a lot, you may want to keep your print size smaller than 16x20 inches.

Measuring focus spread between the nearest and farthest objects you want in sharp focus is simple. Consulting the chart to find the optimum f-stop is also simple.

You wanted a simple approach; well, there it is, staring you in the face. You just need to get past the initial inertia and read through the article. You don't have to figure your own values for circles of confusion or anything; just use the ones the author does and you'll be very well off. You can always revisit and tweak the method if you find you need to later.

Best,

Doremus

[Doremus Scudder]

Alan,

I seem to be moved to comment on viewing and focusing on the ground glass as well. Here's my take:

First, working with a view camera is different than using small or medium format cameras that have viewfinders that you hold to your eye. A common mistake, in my view, is trying to use the LF ground glass to compose the image with, like you would use the viewfinder of your smaller camera. Deciding what you should point your LF camera at should happen in large part before you drag the camera and tripod out and set everything up.

If you have a clear idea of where you want to stand (sit or whatever) and where you want the borders of the scene to be before you set up, then you don't have to spend a lot of time agonizing with the ground glass. You just have to choose a lens that gets your scene on the negative and make some little adjustments to get your movements right and your camera pointed where it needs to be so you're not cropping off any of your desired image.

If you're spending a lot of time moving your camera (and tripod) back and forth and side to side to find the right spot, you're still living in the eye-level-viewfinder world. If you need a viewfinder to help you find the right camera position, use a viewing frame (that's what I do - I rarely have to move the tripod to a better location after I've set it up initially - and when I do, it's usually due to my choosing an impossible shot from the depth-of-field considerations or not having a wide-enough lens with me).

When I work, I find my camera position by walking around and examining the scene (using my viewing frame) till I find the position that gives me the perspective I want. I'll climb up on things, do some deep knee-bends, whatever I need, to find the right place. Then, I'll set up my tripod, place the camera platform under my chin, and adjust my tripod to that height. Only then do I bother to unpack the camera.

If you work like that, you don't even need to spend much time viewing the ground glass; just enough to ensure your scene is there and check whatever focus points you need to apply movements and focus. Sometimes I don't even take time to look at the whole scene projected on the ground glass; I'll just check the edges and then grab the loupe and start focusing. If I don't need movements, I just have to check near and far focus points, position focus halfway between them, choose my f-stop and make the photograph. I don't worry about hot spots, fall-off, etc. As long as I can see the two or three things I need to focus on with my loupe and I know that my desired edges are in the picture, I don't even care if I look at the whole image. I don't check depth-of-field either; I'm confident that I can get my focus points sharp using the near-far method of choosing the f-stop.

I will check for vignetting when needed. And, sometimes I spend a lot of time working on movements to get the plane of sharp focus positioned optimally, but even then, I only need to be able to view my chosen focus points through the loupe.

Best,

Doremus

[Drew Wiley]

Heck, Doremus, I just love spending time looking at that opalescent image on a big ground glass, even if I don't even take a shot. And I'm damn nitpicky about how the frame specifically crops the composition. Moving the tripod an inch either direction might spoil it. When I see a promising spot, I generally stake it out, literally - I stab one of my walking poles into the soil at that exact spot. Then I walk around a little more, seeing if there's an even better spot. That's half the fun of it. The hunt is just as important as the kill.
Depth of field then becomes yet another compositional "hunt". And no rote formula can substitute for that "just right" feel on the ground glass itself, which is double-checked in critical spots with a loupe of course - those places in the composition I want the eye drawn into due to its acute focus, versus where I want the eye to slightly recede. Don't confuse that with gross selective focus; that's OK, but I often aim for a much more subconscious effect on the viewer. A good illusionist does not show his hand.

[Alan Klein]

Probably not. You might ask them.

What do I ask?

[Alan Klein]

Alan,

I seem to be moved to comment on viewing and focusing on the ground glass as well. Here's my take:

First, working with a view camera is different than using small or medium format cameras that have viewfinders that you hold to your eye. A common mistake, in my view, is trying to use the LF ground glass to compose the image with, like you would use the viewfinder of your smaller camera. Deciding what you should point your LF camera at should happen in large part before you drag the camera and tripod out and set everything up.

If you have a clear idea of where you want to stand (sit or whatever) and where you want the borders of the scene to be before you set up, then you don't have to spend a lot of time agonizing with the ground glass. You just have to choose a lens that gets your scene on the negative and make some little adjustments to get your movements right and your camera pointed where it needs to be so you're not cropping off any of your desired image.

If you're spending a lot of time moving your camera (and tripod) back and forth and side to side to find the right spot, you're still living in the eye-level-viewfinder world. If you need a viewfinder to help you find the right camera position, use a viewing frame (that's what I do - I rarely have to move the tripod to a better location after I've set it up initially - and when I do, it's usually due to my choosing an impossible shot from the depth-of-field considerations or not having a wide-enough lens with me).

When I work, I find my camera position by walking around and examining the scene (using my viewing frame) till I find the position that gives me the perspective I want. I'll climb up on things, do some deep knee-bends, whatever I need, to find the right place. Then, I'll set up my tripod, place the camera platform under my chin, and adjust my tripod to that height. Only then do I bother to unpack the camera.

If you work like that, you don't even need to spend much time viewing the ground glass; just enough to ensure your scene is there and check whatever focus points you need to apply movements and focus. Sometimes I don't even take time to look at the whole scene projected on the ground glass; I'll just check the edges and then grab the loupe and start focusing. If I don't need movements, I just have to check near and far focus points, position focus halfway between them, choose my f-stop and make the photograph. I don't worry about hot spots, fall-off, etc. As long as I can see the two or three things I need to focus on with my loupe and I know that my desired edges are in the picture, I don't even care if I look at the whole image. I don't check depth-of-field either; I'm confident that I can get my focus points sharp using the near-far method of choosing the f-stop.

I will check for vignetting when needed. And, sometimes I spend a lot of time working on movements to get the plane of sharp focus positioned optimally, but even then, I only need to be able to view my chosen focus points through the loupe.

Best,

DoremusThat's what I've been doing using a micro 4/3 camera as a viewfinder in BW display if shooting BW and finding the spot before I place the tripod and camera. I also have been using the camera as a meter, but that's another story.

So a few hours ago, I was out shooting with a 75mm lens. The main object was about 4' to 80-100 feet. I focused on the far point using the asymmetrical line where the axis of the standard is. Then tilted the back standard backward to focus the near log up at the tip about four feet away. I set it for f32 and fired away. I just realized though that tilts probably aren't required with a 75mm. At f/32 I was covered from around 3 feet to infinity at coc of .1mm, with the hyperfocal at 6 feet. SHould I have used that and skipped tilts?

So that raises a general question about tilts. When shooting with wide angle lenses like a 75mm, it doesn;t seem even required to worry about them. Just use the DOF tables What's the advise here? Also, the DOF chart I used uses .1mm COC. I could change that if another COC is better. Advise?

[Alan Klein]

No "simplistic" suggestions, nope. But, the method of choosing an optimum f-stop based on focus spread, once mastered, is really, really simple in application. It takes me about five seconds to decide which f-stop is going to work best for any particular shot. It's not arcane in the least.

I seem to keep posting this link, but here it is again, from the LF home page and the article "How to select the f-stop."

https://www.largeformatphotography.info/fstop.html

Heck, if you're lazy or just want the down-and-dirty approach, you don't even have to read the whole article. Just figure out the basic method, print out the tables listed toward the end of the article and paste them on your camera and go to work.

A couple of observations: Most LF lenses work best at or close to f/22. So, there's very little reason to shoot at a larger aperture than that unless you want a shallow depth of field and need the larger aperture for that.

However, if you want lots of near and far things in your photographs to be in focus, there is a very good reason to stop down farther than f/22 when you need the depth of field, despite the slight fall off of performance caused by the (very gradual) onset of diffraction degradation.

You have to enlarge a 4x5 negative a lot to notice diffraction degradation from f/32. How many 30x36-inch prints do you make anyway? Heck, 11x14s from negatives made at f/45 exhibit little or no degradation due to diffraction unless you get out your loupe.

So, in practice, you'll be using a small range of apertures between f/22 and f/45, depending on the focus spread. For those scenes that require stopping down a lot, you may want to keep your print size smaller than 16x20 inches.

Measuring focus spread between the nearest and farthest objects you want in sharp focus is simple. Consulting the chart to find the optimum f-stop is also simple.

You wanted a simple approach; well, there it is, staring you in the face. You just need to get past the initial inertia and read through the article. You don't have to figure your own values for circles of confusion or anything; just use the ones the author does and you'll be very well off. You can always revisit and tweak the method if you find you need to later.

Best,

Doremus

Is this the "simple" table your were referring too towards the bottom of the link your provided? So if I understand, you measure the mm distance on the rail between near and far focus point to determine the f stop. If it falls between two, do you use the smaller f stop?

Do you set the focus point half way between the two or use some form of 1/3 - 2/3 ratio?

Could you explain the N value?

Table of optimal fstops (2)
This shows you the best value of the f-stop to use.
D(mm) F N
1 16.6 19.4
2 22.6 27.4
3 32.2 33.5
4 32.6 38.7
5 32.9 43.3
6 45.2 47.4
7 45.4 51.2
8 45.6 54.8
9 45.8 58.1
10 64 61.2

[JMO]

After reading through this entire (interesting) thread, I’m left with one seemingly simple reaction. After one has taken all the time, effort and expense with LF gear of choice to set-up and make an image on a composition (with needed movements and considering DOF and diffraction considerations), why not make the image at more than one f-stop (whenever possible given wind or other conditions)? Admittedly, I use 4x5 gear and not larger and more expensive film, but I usually take 2-3 exposures of most compositions and vary the aperture to be sure I get what I want as far as DOF. When it comes time to print, I use my light table and a good loupe to help me decide which film(s) to work with. I’m mostly doing landscape photography, so not often wanting to isolate focus narrowly with larger apertures than f22; but if I’m going to take more than one exposure I usually start with the best aperture I’ve determined appropriate, and then stop down one and/or two stops (maybe also changing lens filters or other factors as experience suggests).

[Alan Klein]

After reading through this entire (interesting) thread, I’m left with one seemingly simple reaction. After one has taken all the time, effort and expense with LF gear of choice to set-up and make an image on a composition (with needed movements and considering DOF and diffraction considerations), why not make the image at more than one f-stop (whenever possible given wind or other conditions)? Admittedly, I use 4x5 gear and not larger and more expensive film, but I usually take 2-3 exposures of most compositions and vary the aperture to be sure I get what I want as far as DOF. When it comes time to print, I use my light table and a good loupe to help me decide which film(s) to work with. I’m mostly doing landscape photography, so not often wanting to isolate focus narrowly with larger apertures than f22; but if I’m going to take more than one of exposure I usually start with the best aperture I’ve determined appropriate, and then stop down one and/or two stops (maybe also changing lens filters or other factors as experience suggests).

The problem with varying the aperture is that the DOF will change as well. When I bracket, for exposure not DOF, I change the shutter speed. That keeps the DOF the same on all shots.
I calculate what I think is the correct DOF that will get me the right focus range, then stop down one more stop for good measure. But the bracketing will be done with the shutter. Of course, there are no half shutter speeds, only full stops. You can get 1/3 or 1/2 stops changing aperture. But then the DOF changes. I've done this regularly with medium format shots as it's easy and cheap/ I haven't done bracketing with 4x5 though, except maybe one extra shot on the flip side of the same film holder.

[Vaughn]

Try stopping down instead on a couple images and check out if diffraction is an issue for you at f45 or f/64. Unless getting more DoF is a problem of course, usually it is not. Try printing the negatives to 16x20 or your max size the enlarger will enlarge a 4x5 to (exposing just a 8x10 sheet of paper in a 'typical' area) and see for yourself what f/stop works best for you. The feedback from your prints will help.

[Doremus Scudder]

Is this the "simple" table your were referring too towards the bottom of the link your provided? So if I understand, you measure the mm distance on the rail between near and far focus point to determine the f stop. If it falls between two, do you use the smaller f stop?

Do you set the focus point half way between the two or use some form of 1/3 - 2/3 ratio?

Could you explain the N value?

Table of optimal fstops (2)
This shows you the best value of the f-stop to use.
D(mm) F N
1 16.6 19.4
2 22.6 27.4
3 32.2 33.5
4 32.6 38.7
5 32.9 43.3
6 45.2 47.4
7 45.4 51.2
8 45.6 54.8
9 45.8 58.1
10 64 61.2

Alan,

Yes, this is the table I was referring to. The center column, headed "F" shows the optimum f-stop for a compromise between DoF and diffraction. The column labeled "N" shows what the author (QT Luong) calls the "admissible" f-stop, which guarantees a circle of confusion of 0.066mm on 4x5. The optimal column is what I use.

When the f-stop in the optimal column is larger (smaller number) than in the "N" column, the performance should be even better. When it's larger, you'll end up with more diffraction, but more depth of field.

Hope that's clear.

Doremus

[Doremus Scudder]

Heck, Doremus, I just love spending time looking at that opalescent image on a big ground glass, even if I don't even take a shot. And I'm damn nitpicky about how the frame specifically crops the composition. Moving the tripod an inch either direction might spoil it. When I see a promising spot, I generally stake it out, literally - I stab one of my walking poles into the soil at that exact spot. Then I walk around a little more, seeing if there's an even better spot. That's half the fun of it. The hunt is just as important as the kill.
Depth of field then becomes yet another compositional "hunt". And no rote formula can substitute for that "just right" feel on the ground glass itself, which is double-checked in critical spots with a loupe of course - those places in the composition I want the eye drawn into due to its acute focus, versus where I want the eye to slightly recede. Don't confuse that with gross selective focus; that's OK, but I often aim for a much more subconscious effect on the viewer. A good illusionist does not show his hand.

Don't get me wrong, Drew, I like viewing the image on the ground glass too. It's just that sometimes (more often than I'd like) circumstances keep me from being able to comfortably see everything at once on the gg (things like camera position, setting up in a precarious situation, lots of light coming from behind, wind, rain, crashing waves, whatever...). In those instances, I really like that I'm able to work quickly in those cases, just being sure that the composition I want is "in there" somewhere and then just focusing quickly and exposing.

I pretty damn nit-picky about my borders too. So much so that I almost always crop my enlargements to the exact dimensions and aspect ration that I want and that I think is determined (demanded) by the subject; I don't limit myself to the 4x5 aspect ratio.And, I rarely am able to get borders exactly where I want them from the camera position I choose; I'd need lenses in an infinite number of focal lengths for that. I just choose the next wider lens and make the shot, knowing that the composition I planned is within the borders. If I'm lucky, I don't have to crop too much, but sometimes, say when my 135mm lens is just a tad too long for a shot and the only shorter lens I have with me is a 90mm, and moving the tripod back would destroy the chosen perspective, I just make the shot with the wider lens and crop (and curse the fact that I don't have a 125mm lens with me...).

As for depth of field... My preference and my style is for as much as sharp as possible. Optimizing that with diffraction degradation is pretty straightforward. So, I'll stick with my "rote" method of working. I personally find a lot of out-of-focus areas aimed at "directing the eye" to end up doing just the opposite, i.e., drawing my attention there and distracting from the geometry and leading lines of the composition. That's not to say everything in my prints are razor sharp; I know how to make a foreground object pop out of a background by leaning the focus toward the near, but not enough to really defocus the background; just enough to give that 3D effect, etc. But those things are refinements.

Anyway, the post of mine you were responding to was directed at the beginner's mistake of spending a lot of time finding camera position by viewing the ground-glass image (which Alan doesn't seem to be making, so my post is moot anyway :) ). I do my best to find the precisely right place for the camera before I set up. Yes, I have to scoot the tripod around an inch or so this way or that to get what I really want sometimes because I didn't really hit the mark setting up, but that's just part of the process.

I think we pretty much agree on all of this; I'm just addressing things to those struggling with the basics still, so I'm simplifying my information to that end,

Best,

Doremus

[Doremus Scudder]

That's what I've been doing using a micro 4/3 camera as a viewfinder in BW display if shooting BW and finding the spot before I place the tripod and camera. I also have been using the camera as a meter, but that's another story.

So a few hours ago, I was out shooting with a 75mm lens. The main object was about 4' to 80-100 feet. I focused on the far point using the asymmetrical line where the axis of the standard is. Then tilted the back standard backward to focus the near log up at the tip about four feet away. I set it for f32 and fired away. I just realized though that tilts probably aren't required with a 75mm. At f/32 I was covered from around 3 feet to infinity at coc of .1mm, with the hyperfocal at 6 feet. SHould I have used that and skipped tilts?

So that raises a general question about tilts. When shooting with wide angle lenses like a 75mm, it doesn't seem even required to worry about them. Just use the DOF tables What's the advise here? Also, the DOF chart I used uses .1mm COC. I could change that if another COC is better. Advise?

Alan,

Sorry if I assumed you were making the mistake of using your ground glass to choose the camera position. It seems you've got a good method. I hope I didn't come off as "tech-splaining" things to you.

As far as tilts go: they help if you are able to use them to get your aperture closer to the best-corrected one for your lens, usually f/22. So, if you can adjust your movements to reduce the focus spread so that you can use f/22.6 instead of f/45, then you've made an improvement in resolution and will be able to enlarge that negative more. Whether tilts (or swings) help in this regard depends on the subject. In your case, you may have been able to apply tilt and shoot at f/22, which would have been a slight improvement over your f/32 choice (very slight, really unless you plan on really big enlargements). The only way to really judge if the tilt is helping is to apply it and see if the focus spread improves. If you're already in a situation where the focus spread is really small, like 1mm or a bit more, then you don't have to worry about improving and don't need movements.

And, concerning your choice of CoC: you'll notice that Q.T. Luong, in the article I referred you to, likes 0.066mm for his CoC. He explains why in the article. Basically, it has to do with being able to enlarge more. If you only make 8x10s from 4x5 negatives (and don't crop much) you could likely get by with a much larger CoC.

Best,

Doremus

[Alan Klein]

Alan,

Sorry if I assumed you were making the mistake of using your ground glass to choose the camera position. It seems you've got a good method. I hope I didn't come off as "tech-splaining" things to you.

As far as tilts go: they help if you are able to use them to get your aperture closer to the best-corrected one for your lens, usually f/22. So, if you can adjust your movements to reduce the focus spread so that you can use f/22.6 instead of f/45, then you've made an improvement in resolution and will be able to enlarge that negative more. Whether tilts (or swings) help in this regard depends on the subject. In your case, you may have been able to apply tilt and shoot at f/22, which would have been a slight improvement over your f/32 choice (very slight, really unless you plan on really big enlargements). The only way to really judge if the tilt is helping is to apply it and see if the focus spread improves. If you're already in a situation where the focus spread is really small, like 1mm or a bit more, then you don't have to worry about improving and don't need movements.

And, concerning your choice of CoC: you'll notice that Q.T. Luong, in the article I referred you to, likes 0.066mm for his CoC. He explains why in the article. Basically, it has to do with being able to enlarge more. If you only make 8x10s from 4x5 negatives (and don't crop much) you could likely get by with a much larger CoC.

Best,

Doremus

I appreciate yours and everyone else's help. Just to mention, that in addition to using the micro 4/3 camera to spot the tripod and frame the shot and to "see" in BW, I also use its zoom to determine the LF lens I need. It all saves a lot of wear and tear. Plus franky, I don't like framing upside down. I can't see aesthetically that way.

[Nodda Duma]

Why isn't diffraction considered an optical aberration? It's missing from the conventional list of aberrations.

Late night pondering... :confused:

Because it is not a geometric effect.

[Nodda Duma]

Drew... LOL. I just.... What you saw was the effect of turbulence, integrated over the exposure time of your camera and the response time of your eye. :D

Diffractive effects over a mountain top are too small to be resolved by the eye by several orders of magnitude.


Mark - Diffraction affects different wavelengths differently. I discovered this long ago in reference to the setting sun over sharp ridges where there is extremely clean air, first at Comb Ridge in Utah, then in Kauai. At first I blamed my highly-corrected new lens for the color fringing, but then saw it with my own eyes. The rays were truly bent differently over sharp geological edges in the distance. Something analogous happens with very small apertures, especially in high-magnification optical microscopy. There are very expensive sophisticated methods for correcting this. The primary wavelengths are completely separated, then more precisely re-aligned through electronically controlled magnetic mirrors - add about another $40,000, plus digital output afterwards. There might be similar technology in the latest astronomical equipment - add 400 million dollars, I'd imagine.

[Vaughn]

... Plus franky, I don't like framing upside down. I can't see aesthetically that way.

Probably just because you have not learn to yet. It takes time, one just needs more time under the darkcloth.

[Nodda Duma]

Agreed, Drew, but which other aberrations are ever corrected to perfection, not just reduced or avoided?

All of the basic, third order Seidel aberrations can and have been corrected completely. The Cooke Triplet does that. Higher order / residual aberrations, however...

[Mark Sawyer]

Because it is not a geometric effect.

That makes sense! Thanks!

But is chromatic aberration a geometric effect? :confused:

[Nodda Duma]

That makes sense! Thanks!

But is chromatic aberration a geometric effect? :confused:

Yes, they are wavelength-dependent geometric effects.

Sphero-chromatism: focus vs wavelength
Lateral color: Distortion vs wavelength

Fun fact: Focus is considered an aberration... the only 1st order aberration. Corrected by adjusting focus :D

[Drew Wiley]

Hi Jason - I was hoping you'd chime in with your expertise. But what I saw in each instance was in remarkably clear calm air. Yes, there could have been a rising heat differential somehow, but this was far too crisply defined to be termed heat-wave related. About all I'm qualified to state is that it was some kind of prismatic phenomena, light waves actually being differentially bent or refracted over sharp high edges. I have numerous color photograph of that at high altitude, using highly corrected lenses, and it's significantly more apparent than what you noted. Crisp lines directly over and perfectly copying the details of sharp ridgelines - one line violet, the other distinctly warm hued. Last saw it with my naked eye about 3 years ago in the evening after an exceptional storm at high altitude created the clearest air and deepest blue sky that I've seen in the high Sierra for many decades. The sun was setting the the opposite direction, so it can't be attributed to that. Same case every other time I've seen it - the sun was setting the opposite direction, except atop Kauai, where it was at-mid day. But light can do unusual things in the Islands, bouncing off marine cloud layers below.

[h2oman]

Now what about when a little wind is thrown into the mix... :(

[Drew Wiley]

Then no more crisp lines. This last time I saw this was in fact when the air was unusually calm and clear ... an ominous sign in the high country because it means a big bulldozer of a storm front is right behind it, which was already in full force right over the next divide. I was high enough to get some good shots of that. But I did have one more day to get below timberline, and then when I was snowed in for a few days, I was in the mood for a good long rest in the tent anyway. Had already walked 75 miles on blisters and had another 25 to go. And it was a lovely campsite right next to the river and lots of wonderful unhurried photo opportunities. Drymounted another print from that trip yesterday. One of the colder blizzards I've experienced in September, however.