Macro tools calculations

Hello all,

first to the mods: if this post is misclassified, please move it to where it should be. I do not see any macro subsection in hybrid/digital sections (to me macro applies to everything from film to digital, so having only this section in analog feels like I am missing something)

Now to everyone: I am looking for a way to get good magnification ratio (best would be 5x) while preserving autofocus (hence excluding specific macro lenses that do not have autofocus).

it is possible to find on the web some calculators that take the lens properties and allow a rough calculation of how they would change (in this case MFD minimum focus distance) with extension tubes. I suppose some approximations are made in the process. Would you consider these calculators trustable?
From the few tests I did, if one can trust the calculator, lenses with large MFD only see a small reduction in MFD when using extension tubes/bellows (say, 0.9m gets into 0.8m), so big zoom lenses that have such MFDs (or even higher) won’t work.

I have never found the equivalent calculator for reverse adapters. Is there a way to know, for a given system (i.e. given flange distance) which lens will work in reverse and which one will not, without testing them all? Reverse adapters seem the opposite of extensions: maximum focus distance is then the problem, you often have to be almost on the object to picture. Hence a calculator would be welcome. I do not know though if such a calculator could work without having the details of the internal structure of the lens..

Any advice welcome!

Anaxagore said:

first to the mods: if this post is misclassified, please move it to where it should be. I do not see any macro subsection in hybrid/digital sections (to me macro applies to everything from film to digital, so having only this section in analog feels like I am missing something)

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It's offtopic, but let me address this briefly: it's OK where you placed this and you point towards a problem with the forum structure that we acknowledge - and are indeed working on. I can't say for now when we will change this as it's a major endeavor in many ways. The present proposal is that we will have (much!) fewer and more generic categories, and make more use of tagging to denote whether content is analog, digital, hybrid or 'agnostic' (as in this case).

Anaxagore said:

From the few tests I did, if one can trust the calculator, lenses with large MFD only see a small reduction in MFD when using extension tubes/bellows (say, 0.9m gets into 0.8m), so big zoom lenses that have such MFDs (or even higher) won’t work.

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That's not exactly true, but lenses with a larger max magnification are more likely to be optimized for close-up sharpness.

For example, I've found the Canon EF 100mm f/2 which has an MFD of 0.9 meters to work well for close-up work and autofocus is preserved when using tubes with electronic connections. You just need to use more/longer tubes to get to macro magnification.

Many macrophotographers turn off autofocus. What application are you using it for?

loccdor said:

That's not exactly true, but lenses with a larger max magnification are more likely to be optimized for close-up sharpness.

For example, I've found the Canon EF 100mm f/2 which has an MFD of 0.9 meters to work well for close-up work and autofocus is preserved when using tubes with electronic connections. You just need to use more/longer tubes to get to macro magnification.

Many macrophotographers turn off autofocus. What application are you using it for?

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I am looking at scientific applications where depth of field is important. Without AF, focus bracketing/stacking takes a much longer time than with AF.

I don't know any way to maintain AF at 5X magnification. There is no AF macro lenses designed for 5X and I don't know of any extension tube that maintains AF.

Do you have an approximate distance range you want to be from your subjects when photographing them? I'd start from there.

Chan Tran said:

I don't know any way to maintain AF at 5X magnification. There is no AF macro lenses designed for 5X and I don't know of any extension tube that maintains AF.

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Right, the most you can go with AF macro is currently somewhere in the 1x-2x range.

I would use a geared rail for focus stacking, not AF. That way the perspective won't change between shots. But your requirements may be different.

A magnification of 5.0 can be achieved in several ways. I've noticed that Laowa makes a 25mm lens with M = 2.5 to 5.0. (No AF though)

I can do 5x macro by using the bellow (on a 35mm form factor camera digital or film) but of course no AF.

Have you considered the practicality of the proposed job? At magnifications greater than 1:1 the depth of field becomes EXTREMELY shallow.

This should give you an idea of the problem. Using a 35 mm film or equivalent sensor size camera at 5X (5:1) with a 50 mm lens at f/4 gives a depth of field of about 0.057 mm. Using a smaller aperture won’t help much, but will increase diffraction. I also tried a 25 mm lens in the calculation. The DOF remains about 0.057 mm. By stopping down to f/8 with either lens, the DOF increases to 0.11 mm and increases diffraction as well.

The list of macro lenses at B&H shows mostly lenses intended for 1:1 and a couple at 2:1. One is optimistically rated at 10:1 (intended to be used on a cellphone camera).

https://www.bhphotovideo.com/c/search?q=high magnification macro lens&sts=ma

Here are a few more comments you might find useful.

https://www.google.com/search?q=dep...i4yMS4xuAeDIcIHBjIuNDIuMsgHUg&sclient=gws-wiz

Ian C said:

Have you considered the practicality of the proposed job? At magnifications greater than 1:1 the depth of field becomes EXTREMELY shallow.

This should give you an idea of the problem. Using a 35 mm film or equivalent sensor size camera at 5X (5:1) with a 50 mm lens at f/4 gives a depth of field of about 0.057 mm. Using a smaller aperture won’t help much, but will increase diffraction. I also tried a 25 mm lens in the calculation. The DOF remains about 0.057 mm. By stopping down to f/8 with either lens, the DOF increases to 0.11 mm and increases diffraction as well.

The list of macro lenses at B&H shows mostly lenses intended for 1:1 and a couple at 2:1. One is optimistically rated at 10:1 (intended to be used on a cellphone camera).

https://www.bhphotovideo.com/c/search?q=high magnification macro lens&sts=ma

Here are a few more comments you might find useful.

https://www.google.com/search?q=dep...i4yMS4xuAeDIcIHBjIuNDIuMsgHUg&sclient=gws-wiz

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I think the OP would do it on a digital camera and considered focus stacking for the depth of field problem and thus he wanted to retain AF.

OP, there is no way to get good DoF without stacking. I don't know whether Canon offers software like Nikon's Camera Control (I may have go the name wrong, haven't used it for quite some time) or whether stacking packages like Helicon with shoot stacked images. Look into it yourself.

Chan Tran said:

I think the OP would do it on a digital camera and considered focus stacking for the depth of field problem and thus he wanted to retain AF.

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Indeed, some cameras now have integrated stacking (not only bracketing), which makes the process of capture much faster than when doing the composite on a computer - with the downside that only JPGs/HEIFs are produced.

loccdor said:

Do you have an approximate distance range you want to be from your subjects when photographing them? I'd start from there.

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I would say something between ~25cm and ~85cm.

Anaxagore said:

Indeed, some cameras now have integrated stacking (not only bracketing), which makes the process of capture much faster than when doing the composite on a computer - with the downside that only JPGs/HEIFs are produced.

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My camera does the stacking shots but doesn't do the stacking itself. I have to take those shots and stack them in photoshop. And yes so the shots can be raw.

Anaxagore said:

I would say something between ~25cm and ~85cm.

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at 5X magnification it's hard to get a 25cm distance. Not realistic.

With a given subject distance (subject plane to first nodal point) and specified magnification, we can calculate the required focal length. We can also calculate the image distance.

At 5x and subject distance 25cm (250 mm), the required focal length is approximately f = 208.3 mm.

The image distance (2nd nodal point to image plane) is 1248.8 mm.

For subject distance 85 cm (850 mm), the required focal length is about f = 708.3 mm.

The image distance is 4248.3 mm.

If you reduced the subject distance to, say, 60 mm, then you could get 5X magnification with an image distance of 300 mm. This could be done with an DSLR with a 50mm lens and bellows unit. You might need to add an extension bellows or extension tubes to get enough image distance.

The placement of the first nodal point within the lens assembly reduces the working distance from the subject to the forward-most part of the lens barrel to less than 60 mm.

You’d have to use a strong light to focus as the bellows extension results in a 5.2-stop reduction of light intensity at the image plane.

If my math is correct you will achieve your working distance of 850mm with a ~700mm lens and a bellows extension of 4250mm (at a magnification of 5.0). Good luck with that.

Don't misunderstand me, that's perfectly doable with bellows and rail focusing. But an autofocusing 700mm lens at 5x magnification? That is not realistic.

Are you going to process a very large number of photos? Otherwise I fail to see how in-camera focus bracketing is significant.

Have you read any books about macro/micro photography? Lefkowitz is a good place to start.

Folks, in post #12 above I gave a link to info about a Canon EF mount lens that will do exactly what the OP wants.

loccdor said:

Right, the most you can go with AF macro is currently somewhere in the 1x-2x range.

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I have the Minolta 1-3x AF macro lens ;

That works fine , but at maximum magnification stopping down too much on increases diffraction .
For more DOF only stacking with the lens set to an optimum aperture .

At higher magnification , AF can start to be problematic due to shallow DOF , at 5x it's doubtful AF could be achieved.

Here is an article about the Canon MP-E65mm f/2.8 1-5X Macro Photo lens as mentioned in posts #12 and #19 with illustrative photos.

https://lenzlimphotography.com/2018/06/03/canon-mp-e-65mm-1-5x-macro-lens-review/

Depending on where the nodal points are positioned at the magnification in use, the working distance (subject to front of lens barrel) might be quite short.

Dan Fromm said:

Folks, in post #12 above I gave a link to info about a Canon EF mount lens that will do exactly what the OP wants.

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With which cameras will it autofocus? I thought that was a fixed focus lens?

FotoD said:

With which cameras will it autofocus? I thought that was a fixed focus lens?

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You're right, I should have looked further before posting. Here's a link to the user manual: https://allphotolenses.com/public/files/pdfs/2ba5a8fd9d8fcd35505de50172523178.pdf

On second thought, there are AF extension tubes which transmit data from camera body to lens and back and allow AF lenses (with built-in AF motors) to focus when on the tube(s). Novoflex makes a bellows with similar wiring between camera body and lens.

Fine, wonderful, but these devices all want the lens to be mounted normally. Readily available AF macro lenses are optimized to for magnifications below around 1:1 and are made to be mounted normally. Using one on a long extension device gives up its optimizations.

Another snag is that the OP wants to work at 5:1. On the assumption that the lens will go to 1:1 on its own mount, it will need 4xfocal length mm of additional extension to get to 5:1.

The Novoflex AF bellows has a male mount at the camera end that has contacts like an AF lens, a female mount at the lens end that has contacts like a camera body. A cable carries signal from one end to the other. If I read the specs correctly it offers 180 mm extension.

If the OP has the money -- the Novoflex AF bellows lists for $1,285 -- and can find a good photographer's machinist -- SKGrimes is the likely one, more $$$ -- I suspect that a Novoflex AF bellows' front end can be modified to allow attaching a reversed lens to the bellows. Then attach the bellows' lens mount to the reversed lens. Dumb extension tubes between reversed lens and bellows may be needed to get the desired magnification with, e.g., EF-M28mm f/3.5 Macro IS STM, EF-M28mm f/3.5 Macro IS STM or the EF50mm f/2.5 Compact Macro.

Yes, I was thinking something similar.

850mm working distance will be tough to achieve with the AF macro lenses I have seen.

But if you settle for 250mm it could be done. Hook up the Nikon AF 200mm f/4D ED-IF Micro-Nikkor to a bellows that transfers the 9 CPU pins from camera to the front of the bellows. (well, first you would have to build such a bellows!)

It would take a 1000mm bellows and it would only give a magnification of 4.0. Any higher magnification than that and the working distance would be less than 250mm.