Aperture to depth of field normalisation across various formats

I am setting a very precise portrait brief for 5x4 and would like to open it up to other formats whilst retaining the same dof.
Is there a chart or formula somewhere to calculat what aperture would correlate 150mm and f16 on 5x4 with 50mm on 35mm format? I am guessing f8 ish.
I would need to do the same with MF and dx/apsc formats-- 10x8 too come to think of it
Thank you for your help
regards
Ric

The Rodenstock DOF/Scheimpflug pocket calculator calculates both for all forats from 35mm to 8x10. It will also indicate exposure corrections, if needed.

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Originally Posted by Ricgal

I am setting a very precise portrait brief for 5x4 and would like to open it up to other formats whilst retaining the same dof.
Is there a chart or formula somewhere to calculat what aperture would correlate 150mm and f16 on 5x4 with 50mm on 35mm format? I am guessing f8 ish.
I would need to do the same with MF and dx/apsc formats-- 10x8 too come to think of it
Thank you for your help
regards
Ric

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https://www.google.com/search?q=dof+...ient=firefox-a

Doesn't equivalent dof for equivalent angles of view just factor in the ratio of the film diagonal? That is to say, if you had a short framed with a 90mm lens on 6x7 shot at f/11 then to get roughly the same dof with a 150mm lens on 4x5 you'd shoot at f/22 (double the diagonal, so 11x2 = 22). Not sure I've explained that right but thats the rule of thumb I tend to use.

Of course in that example the ratio is actually about 1.7 not 2, so more like f/18 if were being picky,but you get my drift.

Ric, f/4 on 35mm format has about the same DOF as f/16 on 4x5 where the angle of view is about the same and the print size, viewing distance, and acceptable Circle of Confusion are the same.

When images captured on different formats are viewed at the same size and distance, the DOF is dependent only on acceptable CoF, subject distance, and entrance pupil diameter. This reduces the calculations to math we can manage in the field. It also makes DOF scales on view cameras work with any focal length lens for a standard print size and CoF. My math skills have deteriorated in the 60+ years since high school, so I'll leave it to one of you youngsters to present this subject in a more digestible form.

This site has many versions of their calculator, an explanation of the CoC chosen for each format, and you can pick your own CoC for the charts if you don't like the default for your format.

http://www.dofmaster.com/

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Originally Posted by dave_whatever

Doesn't equivalent dof for equivalent angles of view just factor in the ratio of the film diagonal? That is to say, if you had a short framed with a 90mm lens on 6x7 shot at f/11 then to get roughly the same dof with a 150mm lens on 4x5 you'd shoot at f/22 (double the diagonal, so 11x2 = 22). Not sure I've explained that right but thats the rule of thumb I tend to use.

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It is that easy. You can apply the much maligned 'crop factor' to both the focal length and the f-number.

Dear all- thank you all for your well informed and balanced posts. Being less than a* at maths I will probably check out the DOF calc for iPhone on the site suggested.
All the best
R

Hi !

An important point in your normalization process is that all final prints coming from various cameras, formats and lenses are enlarged to the same final size; and the public looking a them looks at them from the same distance. And that various lenses for the various cameras embrace approximately the same angular field. Those conditions might not be easy, nor really necessary in practice in order to make good portraits.

But let's imagine that those conditions are roughly satisfied, hence the maths involved are very minimal: you can assume that the diameter of the circle of confusion is proportionnal to the film format or to the focal length of the lens in use.

A general rule is that for far-distant objects the same depth of field will be provided if you have the same hyperfocal distance and the same subjet-to-lens distance.

hyperfocal distance = H = f*f/(N*c) where f is the focal length, N the f-number and "c" the diameter of the circle of confusion.

If you assume that you keep the same subject-to-lens distance, the same angular field, and increase the "c" factor in exact proportion of the format, then the (f/c) ratio is kept constant. Hence the same hyperfocal distance and the same DoF will be kept throughout all the situations when the factor (f/N) will be kept constant.

Eventually this is so simple, that no maths are required, even no calculator is required: scale the f-number in the same proportion as the focal length.
Divide the focal lenght by 2 => divide the f-number by 2 = 2 clicks on a classical f-stop scale and you'll keep the same DoF.

Imagine that you start with a 90 mm lens in 35 mm format, this is roughly twice the diagonal of the 24x36 mm format.
in 4x5 the approximate equivalent will be a 300 mm lens, if we do not enter into subtle considerations on different image aspect ratios (1.5 for the 35 mm film format = 24x36 mm format, 1.25 for the 4x5" format).

Assume that you stop down to f/16 with the 300 mm in 4x5", the ratio of focal lengths is 300/90 = 10/3,
the equivalent f-number for (f/16, 300 mm) with the 90 mm will be 16 x 3/10 = 4.8
The conclusion is that, with the above mentioned conditions, the same depth of field as in LF can be achieved, 4.8 is a max f-stop that many 35 mm lenses do provide.

But it might not be a good idea to keep the same subject-to-lens distance. Keeping this distance constant however ensures that perspective rendition is exactly the same throughout all formats and whichever the focal length might be.
And even with the same working distance, various focal lenghts will correspond to various (image/object) magnfication ratios: in portrait work, we are not dealing with far distant objects, and we have to use general DoF formulae valid even for macro work. No simple rule, unfortunately can be given then.

But the rules of thumb are simple : multiply your f-number by the ratio of the focal lengths, and eventually check with a DoF calculator more precisely according to the actual operating conditions.

An interesting, and actually provocative, example of very shallow depth of field in LF portraits is given here in this series of portraits by Henri Gaud, format = 8x10", at 1:1 ratio with an aero ektar lens, focal length 7" = 178 mm, f-number = full aperture = f/2.5
http ://trichromie.free.fr/trichromie/index.php?post/2010/02/20/Hug

Note that a portrait taken at a working distance of 14" is usally considered as an absolute "DON'T" !! An absolute horror, according to classical portrait rules!! Fortunately, here the DoF is so shallow that we do not see too many horrible things, except the eyes of the model on which focusing has been done ;)

Trying to obtain similar results in 35 mm would be a true challenge; I do not know which focal length nor f-stop could deliver similar results, a DoF calculator could give an answer, but my guess would be something like f/1 or so !

On 8x10 that Aero-Ektar would be like a 25mm lens and f/0.35, approximately, in terms of DOF. On 4x5 it's like a 50mm f/0.7. That's at least my calculations.

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Originally Posted by Corran

On 8x10 that Aero-Ektar would be like a 25mm lens and f/0.35, approximately, in terms of DOF. On 4x5 it's like a 50mm f/0.7. That's at least my calculations.

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4x5 has linear dimensions that are half those of 8x10, therefore the equivalent focal length for the same angle of view would be half that of 8x10 - ie from 178 mm on 8x10 to 89 mm (or 90 mm if you wish) on 4x5. Similarly for DoF f/2.5 on 8x10 would be similar to about f/1.3 on 4x5, not f/0.7 - the f-number also gets halved.

Best,
Helen

I'm sorry, what I meant to say was, in terms of 35mm equivalents, those numbers apply. This was in response to the poster inquiring about getting the same DOF effects on small-format cameras.

So,

8x10 -> 178mm, f/2.5 =
35mm -> 25mm, f/0.35

or

4x5 -> 178mm, f/2.5 =
35mm -> 50mm, f/0.7

For a given final print magnification, the only thing that affects DOF for any format is the size of the actual aperture in the lens used (not relative aperture). Of course, lenses don't list the actual aperture, so you have to either guess or calculate.

It amuses me to read all the convoluted derivations photographers go through, all because of the stupid f/stop convention. It's not that they are wrong, it's just...wow.

I wish the apertures had never been expressed in F-stops, and the actual aperture was listed instead. Then DOF would be easy to keep constant between formats, but exposure would change. Personally, it wouldn't bother me if exposure was different with different formats at the same aperture setting...I would expect that anyway. At least the actual image physics would be constant.

The math makes it all equal out to the same thing so what does it matter? Having a constant f/stop scale across any lens on any format makes more sense (to me, anyway) than an aperture setting that is meaningless unless you calculate it out on that given lens/format.

As usual, if you follow what Emmanuel tells you in these matters, you won't go wrong.

if you follow ... what Emmanuel tells you in these matters, you won't go wrong.

.. and f/0.35 ..

... You won't go wrong, sure, Leonard (thanks for the appreciation) except if you push your DoF calculator beyond its reasonable physical limits ;)
Any aplanatic lens, i.e. all those we regularly use in photography, cannot open more than f/0.5
However the parabolic reflector in your car's headlights might represent something like f/0.35 ... image quality, however with such a "lens" might be arguable.

Nevertheless I'm sure that collectors will find here an incentive to buy one of those famous "Barry Lndon's" F/0.7 Carl Zeiss Planars to mimic in 35 mm photography what can be done with a 7" F/2.5 Aero-Ektar!

Another absolute limit of DoF calculators is reached when you demand very small values for the circle of confusion : any reasonable value for this tiny circle cannot be smaller than a diffraction spot. Roughly speaking : N microns where N is the f-number.
Hence the legend says that Saint Ansel never entered "c"-values smaller than 64 microns in His Holy Dof Calculator Made in Carmel, CA ;)

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Originally Posted by SergeiR

https://www.google.com/search?q=dof+...ient=firefox-a

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Hey thanks for awesome link sergei

Thank you Emmanuel
What an awesome answer
particularly
'But the rules of thumb are simple : multiply your f-number by the ratio of the focal lengths, and eventually check with a DoF calculator more precisely according to the actual operating conditions.'
much appreciated
Ric

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Originally Posted by Ricgal

Thank you Emmanuel
What an awesome answer
particularly
'But the rules of thumb are simple : multiply your f-number by the ratio of the focal lengths, and eventually check with a DoF calculator more precisely according to the actual operating conditions.'
much appreciated
Ric

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There's a lesson for us - despite the method having been mentioned twice beforehand, it was Emmanuel's version that got through.

.. despite the method having been mentioned twice ..

Hi, Helen ! Remember the old Roman sentence : "testis unus, testis nullus"; so stating exactly the same thing 3 times, by independant witnesses, who never met before, exactly complies with the ancient Roman wisdom ;)

BTW I checked the rule of thumb against my home-made DOF calculator, with the following entries into the program :
- a fixed subject-to-lens distance used by Richard Avedon in his famous series of protraits in the West, the distance was about 6 feet, say 1,8 meter.
- for the 35 mm camera, a focal length of 90 mm and reasonable f-numbers: 2 - 2.8 - 4 - 5.6 - 8
- in 6x9 cm with a "simulated" focal length of 192 mm delivering exactly the same "filling factor" in "portrait' mode
- in 4x5" with a f.l. of 270 mm and in 8x103 with twice as long 540 mm

I found by a side-by-side comparison of DOF curves that scaling the f-number in proportion of the ratio of f.l. works so well that I doubt that any DOF calculator could be really useful to me in LFphotography in the future, I just have to keep handy an old 35 mm zoom lens with its series of engraved DOF Scales ;-)

"BTW I checked the rule of thumb against my home-made DOF calculator, with the following entries into the program :
- a fixed subject-to-lens distance used by Richard Avedon in his famous series of protraits in the West, the distance was about 6 feet, say 1,8 meter.
- for the 35 mm camera, a focal length of 90 mm and reasonable f-numbers: 2 - 2.8 - 4 - 5.6 - 8
- in 6x9 cm with a "simulated" focal length of 192 mm delivering exactly the same "filling factor" in "portrait' mode
- in 4x5" with a f.l. of 270 mm and in 8x103 with twice as long 540 mm"

But if you are talking about those portrait shots taken in extreme high key he also used 6x6, a Rollei 3.5F with the 75mm Planar and a Mamiya TLR with the 80mm. How do I know? I was at his studio after he had his assitant, Gabriel, call me in because they were having a flare problem on the 3.5F but not on the Mamiya TLR. Reason? The 75mm lens was picking up some stray light that the 80mm on the Mamiya did not see due to its longer length. Cure? Rotate the offending light a couple of degrees.

The “ratio of focal lengths” rule is long established—Stroebel discusses it in View Camera Technique (I have the 1976 3rd ed.). So perhaps we have a fourth independent witness ... The derivation is straightforward—see this article, under, of all things, “Depth of Field and Camera Format.” Do note that the approximation is valid only for a limited range of distances—greater than macro but significantly less than hyperfocal, for all formats compared. This of course assumes the “same picture” criterion that we’ve discussed here several times: among other things, it assumes the same subject distance and angle of view and the same-size final image viewed from the same distance, with the same final-image sharpness criterion for all formats.