Effective apertures.

[scrichton]

Anyone got a simple formula for this. As the 1.4 I have in 35mm is not as dreamy as a 2.5 in 4x5. However a noctilux would be a different matter. Plus I would proabably have money oozing from my pores

[Walter Calahan]

A Noctilux is overrated. Grin.

A Kodak Aero-Ektar is another matter. HA!

http://www.walterpcalahan.com/Cheers/Musings/D3802089-B5EA-4C53-B036-4741BFD94960.html

I just happen to write about one today!

[Dan Fromm]

Huh? What is y'r question? Effective aperture matters only when shooting at magnifications > 1:10. At lower magnifications, aperture set is more than close enough to effective aperture.

Are you thinking about depth of field? If so, please ask again and explain better what you're after.

[scrichton]

Sorry yes I am talking about depth of field in comparison of the formats.

As in f5.6 on 16mm film appears to have a large DOF coverage, whereas 5x4 shallow DOF.

How are these equated between the formats? As the aero ektar looks very shallow in comparison to a 2.5 75mm on my 35mm bessa. Also just to clarify 35mm to 5x4 lens length is roughly a divide LF by 3 for equivical focal length.

[scrichton]

Ok so once again my work time learning has me thinking the effective depth of field at 2.5 on a 5x4 camera with a 2.5 lens will be just slightly less than an f1 (so probably about 0.95 of the old canon dream) At the focal length 60mm in terms of 35mm.

Is this a good or a bad assumption. This is taken from the wikipeadia Depth of Field Article. In the section concerning DOf over format size.


35 mm camera required f/11, a 4×5 camera would require f/45 to give the same DOF

[Nick_3536]

What's the print size? Circle of confusion?

Why do I think we don't want to go down this road -)

[Dan Fromm]

scrichton, wikipedia is like everything else on the 'web, including posts here. Riddled with errors.

Why don't you buy a good book -- I'm tempted to suggest A. A. Blaker's Applied Depth of Field, but it is likely too expensive and suffers from having been written before desktop computers were available -- on basic photography instead of looking for wisdom on the 'web? Blaker's Field Photography might be about right for you.

Short answer to your poorly posed question is that DoF given the size of the tolerable circle of confusion is controlled by magnification and relative aperture. Ain't no simple rule of thumb for comparing situations across formats. Double negative and substandard usage for emphasis.

[scrichton]

Sorry for causing so much pain by asking a question on an observation made by myself and researched with what I have.


Why do I think we don't want to go down this road -)

Nick gets it. A person asks a question that does not meet technical minded people's criteria, then they rip them to shreds over the information being discussed.


Why don't you buy a good book -- I'm tempted to suggest A. A. Blaker's Applied Depth of Field, but it is likely too expensive and suffers from having been written before desktop computers were available -- on basic photography instead of looking for wisdom on the 'web? Blaker's Field Photography might be about right for you.

Said with the subtlety of a bull in a china shop. Thanks next time I'll ask does any know a good book on ..... ?

[Ole Tjugen]

http://www.trenholm.org/hmmerk/

Harold Merklinger adresses an astonishing number of points about focus, DoF, LF cameras and LF camera movements.

[Dan Fromm]

scrichton, I have no opinion about your good qualities or lack thereof. At even odds, you're a wonderful person.

But you're asking questions that suggest you're a beginner and somewhat confused. Your questions are short ones, but they require long answers. That you think a short answer will do suggests you don't understand enough about what you want to learn.

And that's why I suggested that you might want to buy a good book on the basics. You'll learn more than way, and more quickly, than by looking around on the 'web.

I for one am not up to transcribing what's been written better -- more clearly and in greater depth -- than I can write it myself. Why should I type what's been typed already? Wonderful person though you no doubt are, I can't see the point of working that hard to help you. Would you do for me what you want me to do for you? Of course you wouldn't.

Good luck, have fun,

Dan

Oh, and by the way. When you post questions on the 'web, you should be prepared to receive some responses that don't please immediately.

[scrichton]

Thanks Ole. I'll read through these. Seems to be an amazing resource maybe it could justify a sticky or announcyment on the forum somewhere?

[Mark Sawyer]

Personally, I find myself more and more using ineffective apertures...

[scrichton]

Apologies again,

Dan I'm sorry about the tone of the response. Just reading through the posts from yourself they do read in the way of an attack. Maybe this is just the way I would use language and yourself being taken the wrong way by me.

I was honestly not aware that the question posed had such an amazingly underlying complexity. My solution of a simple answer was not to be.

I did pose this question out of an observation that the pictures I have taken on my nikon with a 50mm f1.2 or the 40mm 1.4 on my voigtlander do have similar depths of field as the aero ektar and dallemeyer pentac. Which are roughly as the the wikipedia article states a similar number of stops apart in terms of 35mm -> 4x5 open apertures, especially seeing as the focal length conversions give similar equivical focal lengths. A 135mm at 4.5 also looks very like a leica 35mm 1.4 wide open.

Once again sorry, I will in the future choose my words more carefully and try to explain with more detail what I am trying find out.

[Eric James]

What's the print size? Circle of confusion?

Why do I think we don't want to go down this road -)

And what to you consider sharp? And from what distance will the image be viewed?

There was a similar question posted on the photo.net Nikon forum a while back; someone had answered with a simple but enlightening diagram - I haven't been able to find the thread, but I did find this:

http://photo.net/learn/optics/dofdigital/

[Gordon Moat]

Anyone got a simple formula for this. As the 1.4 I have in 35mm is not as dreamy as a 2.5 in 4x5. However a noctilux would be a different matter. Plus I would proabably have money oozing from my pores

The main thing to consider is that when you match Field of View across formats, is that the lens focal length becomes longer as the format increases.

Very, very, very, very rough . . . . A loose interpretation is that for a similar FoV at the same camera to subject distance, an f8.0 lens on a 4x5 camera would have near the DoF (Depth of Field) of an f1.8 lens on 35mm. An f6.7 would be closer to an f1.4, so an f5.6 would be very short DoF when used wide open on a 4x5 camera.

The other aspect to consider is using tilt or swing to alter the plane of focus. This is often done for selective focus. While possible with tilt/shift lenses on smaller format cameras, the amount of variability and movement can often be greater on view cameras, making selective focus results appear different from larger cameras.

In practice, shooting wide open aperture on a view camera is not as easy as when using smaller cameras. It helps to have the camera on a tripod, but if your subject moves slightly forward or back they can fall out of the plane of best focus.

The best arguement I have heard for fast lenses in 35mm was for low light conditions. This is one realm where larger formats are tougher, since exposure times increase. It does strike me as a little odd to see so many new cameras sold with f3.5 to f4.5 zoom lenses (35mm or half frame D-SLR); mostly it makes me appreciate that the f5.6 (and one 21cm f4.5) lenses I have for my 4x5 camera are really fast lenses.

Check out pCAM software for PalmOS. This makes visualizing lenses and formats much easier. Available at:

http://www.davideubank.com/

Ciao!

Gordon Moat
A G Studio (http://www.allgstudio.com)

[Ron Marshall]

What I have written is not intended to be rigorous, just an observation.

There is an online DOF calculator that states the algorithm they use only has four variables: Circle of confusion (CoC), focal length, aperture and subject distance. It is not format dependent, beyond using format to select a CoC.

I order to make a rough comparison of DOF between formats, I used the same CoC and the same subject distance in a series of calculations. I varied the focal length, then adjusted the f-stop to maintain the same DOF.

I used focal lengths equal to the diagonal of various formats: 35mm (43), 6x7 (88), 4x5 (153), 5x7 (209).

I found that the f-stop required to have the same DOF across all formats was equal to the ratio of the area of the format to that of 35mm. For example, for 35mm I chose 43mm and f1, then to have the same DOF with 6x7 (88mm focal length) I needed f4.4, the ratio of the area of 6x7 negs to 35mm negs. 4x5 needs f13, and 5x7 needs f25.

The important consideration here, is that I am not changing the CoC.


This is the link to the DOF calculator:

http://bobatkins.com/photography/technical/dofcalc.html#calc

[Oren Grad]

If the issue is how to match a subjective impression of "dreaminess", I suspect that DOF calculations are mostly beside the point. Even if you find the aperture for a different focal length that matches the calculated DOF for appropriately scaled CoC, it doesn't mean the subjective "feel" of the picture will be the same. Not that DOF is irrelevant - obviously a pan-focus picture would entirely defeat the purpose - but it's only a starting point. The optical character of the design, in both the in-focus areas and the out-of-focus areas, has a large effect as well.

I just played with an online DOF calculator. For a subject at 6 feet, the calculated DOF for a 210mm f/5.6 lens at open aperture on 4x5 comes out very similar to that for a Noctilux at f/1 on 35mm. But a modern 210mm plasmat, even flat out, doesn't render like a Noctilux. The respective design tradeoffs chosen by the engineers are very different.

[Ron Marshall]

Oren, what DOF calculator did you use? I would like to compare a few to see how much their calculations differ.

[Ron Marshall]

Here is a good dicussion of DOF:

http://home.online.no/~gjon/davisdof.htm

[Oren Grad]

Ron, I happened to grab this one (http://www.dofmaster.com/dofjs.html). But if you Google "depth of field calculator" you'll find others. Assumptions may vary across different calculators, so the results may come out a bit different, but the basic point remains. It's not hard to find calculated DOF numbers that match across pairs of lenses that will render very differently.

Edit: I should add, what does change if you hold the distance and the overall calculated DOF constant is the distribution of the focus depth in front of and behind the plane of focus. That will affect image character, and it just underlines the point that there's no straighforward mapping - all sorts of things change as you scale formats and focal lengths.

[Ron Marshall]

Thanks Oren. Yes of course there are other considerations such as Bokeh involved, I am not at all disputing that. I only mentioned DOF because it can be quantified.

[Oren Grad]

Here's another observation. It's been said that one doesn't usually see Noctilux-like effects in typical 50mm f/1.4 lenses - it's necessary to go to f/1.2. In the 35mm focal length, it's not clear what you'd need - for example, I don't have a good sense for how the C/V Nokton renders.

But how much of that is due to the wide aperture and the correspondingly narrow DOF, and how much is due to the fact that engineers balance aberrations differently in designing an f/1.2 lens than they do in designing an f/1.4? I don't know.

[Ron Marshall]

But how much of that is due to the wide aperture and the correspondingly narrow DOF, and how much is due to the fact that engineers balance aberrations differently in designing an f/1.2 lens than they do in designing an f/1.4? I don't know.

Probably DOF plays a minor role in how an image is rendered with such lenses, but I don't either.

[Dan Fromm]

Apologies again,

Dan I'm sorry about the tone of the response. Just reading through the posts from yourself they do read in the way of an attack. Maybe this is just the way I would use language and yourself being taken the wrong way by me.

I was honestly not aware that the question posed had such an amazingly underlying complexity. My solution of a simple answer was not to be.

I did pose this question out of an observation that the pictures I have taken on my nikon with a 50mm f1.2 or the 40mm 1.4 on my voigtlander do have similar depths of field as the aero ektar and dallemeyer pentac. Which are roughly as the the wikipedia article states a similar number of stops apart in terms of 35mm -> 4x5 open apertures, especially seeing as the focal length conversions give similar equivical focal lengths. A 135mm at 4.5 also looks very like a leica 35mm 1.4 wide open.

Once again sorry, I will in the future choose my words more carefully and try to explain with more detail what I am trying find out.Well, I can be excessively blunt. If I'd meant to attack your personally I'd have done so much more directly. If you think I was going after you, I apolgize. That wasn't my intent.

One of the problems with apparently simple questions is that sometimes they aren't.

And I plead guilty to a lack of patience with people who seem to ask questions first without first trying to find answers and failing. Apparent lack of effort bothers me. This is one of my weaknesses. Go take a look at questions posted on, say, photo.net. When I read some of them an image of a young bird, mouth wide open, begging to be filled with with partially digested worms and bugs comes to mind. Most people who come to formats larger than 35 mm are capable of feeding themselves.

Good luck, have fun,

Dan

[scrichton]

Well, I can be excessively blunt.

and I'm a tetchy little ba@*!ard. So call it quits.

[C. D. Keth]

Just go buy a book called "Basic Photographic Materials and Processes"

It has the answer to basically every technical question about photography you can ask.