Does changing aperture move the focus point

[tenniss_balls]

Hello,

If I focus the camera at a brighter aperture so that I can see the object on the ground glass, and then change the aperture does that move the focus point or just change the depth of field?

I have never made an exposure and about to make my first attempt.

I have purchased a fresnel screen yesterday does anyone have tips for focusing when it's dark?

[tenniss_balls]

The lens is a Goerz 12" dagor it's barrel mounted and I have the sinar copal shutter.

It's too dark to see. As I close the aperture it seems to get sharper. I'm focusing on some wood grain and it gets sharper and then it gets too dark to see.

8 x 10 film is so expensive i'm loath to pull the trigger so to speak.

Think i'll wait for the fresnel and see if that helps.

[Peter De Smidt]

Ok. Well, use some ingenuity. Place a flashlight at a normal subject distance pointed at the camera. Focus (with a good loupe) wide open. Stop down. Check focus. A Fresnel will not help with this at all.

[Bernice Loui]

Focus shift from full aperture to stopped down as exampled by stopping down to f16 or smaller, modern view camera lenses exhibit about zero focus shift. They were designed to be focused full aperture then stopped down to taking aperture, as viewed on the GG.

Vintage lenses like Dagor, focus shift depends on the specific example of Dagor. Some have focus shift, others very little focus shift from full aperture.

Keep in mind what is focused on IS what will be a true focus or the actual focus plane. This can be adjusted and bent by applying camera movements. Stopping down the lens results in more of the image going into apparent focus or the appearance of "sharper" but not in true focus as what is at the set plane of focus.

Learning how to see and view the stopped down image on the GG is an essential part of learning how to view camera. While a fresnel might help, it can be a problem depending on lenses used and image making conditions. Fresnel viewing aids are not a panacea cure-all view camera GG visual realities. If the fresnel is not properly installed, it will not properly register the view camera image to the film in film holder causing blurry image where the focus area was set. While a fresnel can produce a brighter GG image on axis of the GG and fresnel combo, fresnel lenses have grooves (how they work) which can hinder the view camera GG image when a magnifier is used to assess actual focus.

There are other factors from alignment-registration from GG to film in film holder distance which must be within a specific tolerance. Camera alignment/precision of lens to film holder area and more.

If you're un-willing to "pull the trigger" due to cost of 8x10 film, why do 8x10 film? Burning film is an essential part of learning how to view camera.


Bernice





The lens is a Goerz 12" dagor it's barrel mounted and I have the sinar copal shutter.

It's too dark to see. As I close the aperture it seems to get sharper. I'm focusing on some wood grain and it gets sharper and then it gets too dark to see.

8 x 10 film is so expensive i'm loath to pull the trigger so to speak.

Think i'll wait for the fresnel and see if that helps.

[Bernice Loui]

GOOD suggestions here, based on real world view camera experience.


Bernice



Ok. Well, use some ingenuity. Place a flashlight at a normal subject distance pointed at the camera. Focus (with a good loupe) wide open. Stop down. Check focus. A Fresnel will not help with this at all.

[tenniss_balls]

OK thanks for the replies. It was difficult to see the wood grain because the angle of the light was not reflecting back to the lens where I wanted to focus. I moved the light and checked wide open and stopped down. It doesn't look much different. Sharper and more contrasty.

Thanks for the flashlight suggestion.

I have to say working and thinking about every aspect of your imagery is very theraputic! And i'm amazed by the image on the ground glass. I'ts surprising what details you can see through the loupe.

The loupe I have is a Silvestri. Not too sure of it's quality.

Is there a particularly good quality loupe which is recommended?

[Alan Klein]

It can, varies from lens to lens. Check you focus after stoping down.

I have Nikkor Schneider and Fujinon. Do these or not?

In any case, why would LF lenses change focus points and DSLRs don't? Every shot one takes with a DSLR stops down when you press the shutter. I've never heard of this problem. I've got enough problems learning LF. Let's not create more problems for me. :)

[Bob Salomon]

I have Nikkor Schneider and Fujinon. Do these or not?

In any case, why would LF lenses change focus points and DSLRs don't? Every shot one takes with a DSLR stops down when you press the shutter. I've never heard of this problem. I've got enough problems learning LF. Let's not create more problems for me. :)

Guess you never used an Imagon. It changes focus with each disk setting used. So you have to focus at your choice of setting, not widen open.

[Mark Sawyer]

Berenice was quite right in post #5.

I'll add that focus shift is the result of spherical aberration, which is also the driving force behind the soft focus effect. The outer area of the lens is focusing on a slightly different plane than the center. As you shut down the aperture, outer areas of the lens are blocked, and the dominant focus shifts to the center of the lens.

Early Dagors still had a bit of spherical aberration, hence the famous "Dagor Glow". By the time Dagors were coated, the spherical aberration had been corrected and the glow and focus shift were gone.

If your lens doesn't have spherical aberration, it won't have focus shift. And any sharp modern lens will be well-corrected for spherical aberration.

[Mark Sawyer]

Guess you ever used an Imagon. It changes focus with each disk setting used. So you have to focus at your choice of setting, not widen open.

Quite right! Each different aperture disk allows light from different parts of the lens. As the Imagon has lots of spherical aberration (it is a soft focus lens, after all), the focus shift is quite pronounced. ALL soft focus lenses need to be focused at the taking aperture.

[Dan Fromm]

The lens is a Goerz 12" dagor it's barrel mounted and I have the sinar copal shutter.

It's too dark to see. As I close the aperture it seems to get sharper. I'm focusing on some wood grain and it gets sharper and then it gets too dark to see.

You're confusing two effects.

Dagors are known to shift focus on stopping down. This should cause the image on the GG to lose sharpness.

Most, not all, lenses' gain coverage and, for a while, sharpness on stopping down. This because stopping down reduces some aberrations, off-axis ones in particular, until diffraction, which increases on stopping down, overwhelms the gains from reducing off-axis aberrations. And yes, stopping down increases depth of field.

As an aside, I've always wondered whether all Dagors and dagor-type lenses shift focus on stopping down. This because (a) Goerz Dagors' were manufactured for many years and were recomputed from time to time and (b) my Boyer Beryls, which are Dagor clones, don't shift focus on stopping down.

If you have a 4x5 camera, use it to take two test shots with your 12" Dagor, one wide open and the other at your intended shooting aperture. Set the camera up at an angle to something like yardstick (if you're going to be shooting close) or a brick wall or picket fence (if you're going to be shooting at some distance), mark the subject so you'll know where you focused, and go.

[BrianShaw]

It might be worth exploring the question using a depth of field calculator and the parameters of the shot you are planning. With the exception of Imagon, I would think that under “normal conditions” dof accounts for any minuscule focus shift that may occur.

[afotandolaciudad]

Another point: focus shift while stop down happens with convertible lenses when using converted. So seems to be related with alterations in the iris position or configuration. This barely occur with smaller formats.

[tgtaylor]

Well I have the Nikkor 135mm AF DC f2 lens and the Nikon instruction manual says to focus after setting the DC (defocus image control) ring or the subject will be out of focus. The purpose of the DC ring is to control the focus of the foreground or background. So I would focus at the shooting aperture.

Thomas

[BrianShaw]

Well I have the Nikkor 135mm AF DC f2 lens and the Nikon instruction manual says to focus after setting the DC (defocus image control) ring or the subject will be out of focus. The purpose of the DC ring is to control the focus of the foreground or background. So I would focus at the shooting aperture.

Thomas

It’s not likely for that lens to be used on a large format camera!

Even in its intended application... is “unique”.

[lassethomas]

In any case, why would LF lenses change focus points and DSLRs don't? Every shot one takes with a DSLR stops down when you press the shutter. I've never heard of this problem. I've got enough problems learning LF. Let's not create more problems for me. :)

Focus shift is well known for some (D)SLR lenses too. For example, the Zeiss Contax 45mm f/2 for c/y mount has a ridiculous amount of focus shift.

[Drew Bedo]

Maybe testing the lens described in the OP would help. However, shooting LF film today can be costly and takes time. A slightly inclined ruler or yard stick/meter stick under strong flood lights would allow a visual check of focus shift as it is stopped down.

[Alan Klein]

If you can't handle this, you had better give up now and stick with your digi's

What are you saying? Do I have to refocus with my Nikkor, Fujinon and Schneider lenses after I stop down on my 4x5? I haven't read that anywhere.

[Alan Klein]

Maybe testing the lens described in the OP would help. However, shooting LF film today can be costly and takes time. A slightly inclined ruler or yard stick/meter stick under strong flood lights would allow a visual check of focus shift as it is stopped down.

Have you ever done this, Drew? Was there focus shift?

[Jim Noel]

I have never had the problem with any of my Dagors, in fact I have never had to stop down when using any lens other than a few from the 18th century. I do recheck focus after stopping down and if there is any focus shift, it is too small to detect on the ground glass.

[neil poulsen]

The lens is a Goerz 12" dagor it's barrel mounted and I have the sinar copal shutter. . .

I will not tolerate focus shift. If I suspect that a lens has focus shift, it's going to get SOLD! And, longer Dagors are known to demonstrate this aberration. Life is complicated enough as it is; I will not add focus shift to that mix. :)

There are too many other options in a 12" lens; go for one of those. For example, I recently purchased a Fuji, 300mm f5.6 with inside lettering for 8x10. This lens has excellent coverage, and I'm not worried about focus shift with this lens. It's single-coated; but, I decided to stick with single-coated lenses for 8x10. (It's less expensive.) One nice thing about this lens, it takes 77mm filters, versus something larger.

I'm also seeing some decent DBM options on EBay.

[Greg]

How I have checked my vintage lenses for a focus shift:

1. Set up my palm sized LED flashlight on one side of my basement. It has 4 rows of 6 LEDs in a rectangular pattern.
2. On the other side of the basement I set up my Sinar at an equal height to the LED flashlight.
3. Set my back standard to the "0" setting and focus with the front standard with the lens wide open.
4. Stop down the lens and move the back standard back and forth noting the "range of focus".

If the "0" setting is in the center of the "range of focus", then there is no focus shift. If the "0" is not in the center of the "range of focus", then I have a focus shift.

addendum: when I wrote "center of the range of focus", I should have said the approximate center.

[Drew Bedo]

Have you ever done this, Drew? Was there focus shift?


No, I have never done exactly that. I have not felt the need to.

I do not recall setting up a shot where some focus shift was that critical to the composition.

In all openess though; I am visually impaired with no vision in my formaerly dominant eye and something like 20/150 vision in my "good" eye. When doing table-top compositions I often set high contrast focus aids in several places when focusing wide open. I get some shots I am really proud of and many that I just don't show anyone.

However, my professional experience, before losing my sight, involved medical imaging with isotopes. We did a LOT of calibration and QA work before setting up the equipment for a routine patient study.

The OP identified an effect that seems to be a variable for his way of doing LF photography . . .OK, my suggestion is based on what I know of LF technique and years of isolating variables in an imaging process. Its a cheap and not overly complicated or elaborate bit of experimentation. Shouldn't be much to do it and it could give some answers.

As an aside: My working set of lenses are of mid to late 1980s vintage by Nikon, Fuji and Rodenstock. I just can't make my photo budget take the jump to the latest AP
O formulations. Looking for s bargain on a Petzval that will cover 8x10 though.

[Lachlan 717]

Shine a laser pointer onto a wall in the dark. Bung a Bahtinov mask on the lens, stop down and use the defraction spikes to focus. Done.

[Alan Klein]

No, I have never done exactly that. I have not felt the need to.

I do not recall setting up a shot where some focus shift was that critical to the composition.

In all openess though; I am visually impaired with no vision in my formaerly dominant eye and something like 20/150 vision in my "good" eye. When doing table-top compositions I often set high contrast focus aids in several places when focusing wide open. I get some shots I am really proud of and many that I just don't show anyone.

However, my professional experience, before losing my sight, involved medical imaging with isotopes. We did a LOT of calibration and QA work before setting up the equipment for a routine patient study.

The OP identified an effect that seems to be a variable for his way of doing LF photography . . .OK, my suggestion is based on what I know of LF technique and years of isolating variables in an imaging process. Its a cheap and not overly complicated or elaborate bit of experimentation. Shouldn't be much to do it and it could give some answers.

As an aside: My working set of lenses are of mid to late 1980s vintage by Nikon, Fuji and Rodenstock. I just can't make my photo budget take the jump to the latest AP
O formulations. Looking for s bargain on a Petzval that will cover 8x10 though.

I'm glad you're still shooting. That's great.

[ridax]

I will not tolerate focus shift. If I suspect that a lens has focus shift, it's going to get SOLD! And, longer Dagors are known to demonstrate this aberration. Life is complicated enough as it is; I will not add focus shift to that mix. :)

I abide by quite the opposite rules. Any focus shift is due to the spherical aberration (SA), and it is the spherical aberration that makes the out of focus rendition beautiful. The negative SA makes the out of focus background rendition great at middle to small f-stops, and the positive SA makes the out of focus foreground rendition great when a lens is used wide open. Both mean more or less focus shift. A lens completely free of any focus shift is free of any SA and thus renders any out of focus image zones totally ugly. For me, it is this lens that's going to be sold as soon as possible.

In their background out of focus rendition, Dagors are the greatest of all the lenses ever made - because they have a lot negative SA at all f-stops from f/10 to f/45. And that just can't exist without the focus shift. So the only choices are (1) to get used to that focus shift or (2) tolerate the ugly out of focus rendition of the more "technically perfect" lenses or (3) stay with the F/64 style and have nothing out of focus in the images. I've chosen the first of the above.

[xkaes]

Enlarging lenses can exhibit focus shift as well. It's worth checking yours out for this -- although this is usually not possible with simply a grain analyzer. Just focus wide open -- as you probably already do -- then stop down and make a small print at high magnification.

[Tin Can]

My 2 SF AKA Knuckler Cooke also

I had a lot of conflicting advice, especially the printed by Cooke pamphlets, they changed their printed story...

[Bernice Loui]

Most "entertaining" lenses that often have focus shift with aperture are sorta-focus (soft focus) lenses..
Many trials and tribulations to learn how to properly focus these Sorta-Focus lenses..

Bernice

[xkaes]

Yes. Fujinon specifically states to focus its SF lenses stopped down to the taking aperture -- which usually isn't stopped down much anyway -- and focusing on a "catchlight" in the scene.

http://www.subclub.org/fujinon/lensmanual.pdf (http://www.subclub.org/fujinon/lensmanual.pdf)

[Tin Can]

It took me years to get comfortable with wide open SF

I have lens variety, now

the more I research big Pinhole with many books

the better I see

[John Layton]

XKAES...I cannot seem to access that Fujinon brochure on my computer...but how old is it? And to which specific lenses/vintages does it refer?

While I sometimes, even with my quite modern lenses (and assuming I have some good catch lighted textures) will check the actual focus with a lens stopped down...I more often am stopping down to simply check DOF, finding it a risky proposition to entrust a relatively darkened image to indicate a precise focus plane. I'd therefore be quite surprised at Fuji's recommendation unless the lens(es) in question exhibited quite visible shifts in focus.

Then again...do keep in mind that Ansel Adams reflexively knew just how much to correct (without visually re-checking his focus) the focus-shift prior to making his wonderful "Moonrise" photograph!

[xkaes]

Fujinon is only talking "focusing stopped down" regarding its SOFT FOCUS lenses.

The manual is the only one that they produced in the '70s & 80's. They must have produced new manuals during the CM-W period, but I don't have that.

DOES ANYONE HAVE ONE TO SHARE????

Anyway, if you can't access the PDF file, try another BROWSER or OPERATING SYSTEM -- it's there. You are probably being blocked by your ISP "insecurity".

[Drew Wiley]

Even the last of the regular Dagors, the splendid multicoated 14 inch Kern, exhibited a bit of focus shift until a third of a stop before f/11, and none further down. No big deal. If you can't stand the idea of refocussing a tiny amount, just start out at f/11 instead. It will still be plenty bright.

As far as old timers went, Dagor focus shift probably wouldn't have any visible difference in a contact print, that is, independent of depth of field issues. And per immortalized St Ansel, who we all know did everything photographic better than everyone else who has ever lived, or ever will... uh,er ...relatively few of his 8x10 negs were particularly sharp by modern standards, including Moonrise. But they generally worked reasonably well up to around 20X24 print size, which is less than a 3X magnification. Double that, and detail in many of them gets mushy fast. That's why he often had his very large prints printed lower contrast and somewhat warmer in tone by a commercial lab better equipped than himself. Lower contrast disguised those flaws better; and as one backed off to view the image, it took on a more poetic gentler feel rather than his classic, hard contrast, more dramatic version. I'm not necessarily referring to Moonrise per se, which had all kinds of printing issues, but to a number of his most famous landscapes. Most sheet films per se were pretty damn grainy back then, among the numerous logistical issues which he faced to a greater extent than we do today. He wasn't using a huge precision aerial film camera like Bradford Washburn often did.

Per practice, I always double focus. First, at full aperture relative to the general composition, including all movements. Second, halfway stopped down to my intended working aperture, in order to home in on just key elements I want to be in perfect focus within the overall scheme of things. Since the image will be rather dim the second time, I seek out some bright little highlight or line in the key area which makes life easier. With closeups, I might temporarily add a little
sparkly aluminum foil to a key spot, or in a cave a tunnel, a laser pointer beam. Since people do tend to get nose up to even my large prints, it's important to choreograph their visual response exactly the way I want it, with the eye seeking out detail, but then following that with respect to the greater composition, so that it's effective at both level - both close up and backed away from. A fun challenging game at least.