Enlarger lenses vs. camera lenses when reversed?

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Thagomizer
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Enlarger lenses vs. camera lenses when reversed?

Post by Thagomizer »

Hi all;

Just wondering what sort of overall differences in performance there might be with lenses in the 24-35mm range between enlarger lenses and SLR camera lenses? I'd be using them for single shots, rather than stacks, reversed on a longer lens, teleconverter, extension tube, or on the camera body directly. I know it's going to depend on the specific lenses involved, but I'm curious as to whether there are basic differences between the two types of lenses that can be generalized regardless of the particular models in question? I don't have any enlarger lenses in this focal length range, but several SLR lenses with which I've done a bit of playing with. Would a short focal length enlarger lens offer any improvements in performance, image quality, or usability for my intended use?

The following are with a reversed Pentax 35mm f2.4 "plastic fantastic" reversed directly on Pentax KP. Built-in flash with Pringles tin extender/diffuser. Handheld single shots.

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ChrisR
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Post by ChrisR »

Camera lenses have to be "retrofocus" or "inverted telephoto" if the "flange focal distance" (the distance between the flange where the lens attaches and the sensor) isn't long enough.
It applies particulalry therefore, to short focal length lenses on SLRs designs where the mirror has to be cleared.
That imposes restrictions on the designer of the camera lens that the enlarging application does not.

Having said that, if you're comparing an enlarger lens designed & made in 1960 with a modern camera lens, you would hope to see technical improvements.
Even some old designs of camera lenses give images which are "very good" when reversed - but not the very best.
Chris R

Sym P. le
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Post by Sym P. le »

An enlarger lens needs to pick up a flat scene from close range. Inherently, it will be closest to the subect at the center while further away at the edges and will be compensated for this. Furthermore, intended users of these lenses demand exacting performance from corner to corner across this plane.

Standard lenses do not need to meet this criteria so designers are free to choose their own nuances. Your images, which I find aesthetically pleasing, are a perfect example. They are reasonably sharp in the center (the easiest part of any lens design), and defocus away from center. The colours can be said to be warm.

An enlarger lens used for this same scene would show a sharp plane of focus across the image oriented w.r.t. the optical axis. Defocus would be in front of or behind this plane more so than out from the center.

There are implications in stacking as well. A lesser enlarger lens may not be exactingly planar but may still be brought into closer focus at the corners whereas standard lenses may not.
Last edited by Sym P. le on Sun Mar 08, 2020 10:57 am, edited 1 time in total.

Sym P. le
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Post by Sym P. le »

Reversing a lens is about utilizing the inherent numerical aperture to achieve greater resolution. Where most standard or enlarging lenses were designed to have the broader scene in "front" of the lens, macro photography is just the opposite.

Lou Jost
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Post by Lou Jost »

I think there is another important consideration when reversing lenses or using enlarger lenses. The projected image on the sensor is usually just a small crop of the whole image projected by the reversed lens or the enlarger lens. The smaller the crop, the greater the drop in resolution (in lp/mm). So for example, if you are using a reversed macro lens that was designed for a 35mm sensor, and you use enough extension to get 2x, you have cropped the aerial image projected by the reversed lens by a factor of 2. So I think the central resolution (in lp/mm) of the projected aerial image should be only about half the central resolution of the image projected at 1x.

Lenses designed for smaller sensors generally have higher resolution (in lp/mm) than lenses designed for larger sensors. This will still be true when reversed. For a given reversed lens (assuming it is not tightly optimized for a single magnification), central resolution should be at its best when the reversed magnification roughly equals the ratio of the camera sensor divided by the film or sensor size the lens was designed to image. So for example, generally a micro-four-thirds lens reversed at 2x (or a little bit more to improve the corners) on a FF camera should do very well, and should have better central resolution than a FF lens reversed at the same magnification. I have tested this using the Nikon 60mm D versus Olympus MFT 60mm lens, and the results confirmed this. I posted this here:
https://www.photomacrography.net/forum/ ... highlight=

In general, a reversed lens should deliver the highest central resolution when the projected image is not cropped. That means that if you use a FF sensor, for 2-3x you should use reversed MFT lenses, or enlarger lenses meant to enlarge smaller negatives; for 1x you should use FF lenses. For higher magnification you should look for lenses designed for even smaller negatives or sensors.

rjlittlefield
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Post by rjlittlefield »

Would a short focal length enlarger lens offer any improvements in performance, image quality, or usability for my intended use?
Maybe, but it's not clear exactly what they'd be.

While I'm prattling on, please be thinking of an answer to this question: What is it about your current images or workflow that you would particularly like to improve?

You've said "single shots", and you've shown us a couple of examples that appear to be around 1:1 or a little higher on an APS-sized sensor (Pentax KP).

I notice that the images have wonderfully smooth bokeh, both in front and behind focus, and I'm not seeing any significant problems with either color fringing (radial CA) or color shifts due to longitudinal CA. Central sharpness looks fine, and there's nothing in focus on the edges/corners to worry about.

When I search on Pentax 35mm f2.4 "plastic fantastic" I get pointed to the Pentax-DA 35mm F2.4 AL, for which there's an extensive review at https://www.pentaxforums.com/reviews/pe ... ction.html . If I'm reading it properly, they're pretty happy with the lens's glass, giving it high marks for sharpness, control of flare, small amount of chromatic aberration ("purple fringing" on a slightly OOF hard edge), and good bokeh with background foliage (despite only 6 straight blades in its aperture).

Granted, their tests were at long distance focus, not 1:1, so it's very likely that the lens picks up some curvature of field and some spherical aberration (loss of contrast for fine detail) due to the close focus. But still, "the proof is in the pudding", and the shots that you've shown look fine to me. Flat fields are important if you're shooting flat subjects, but for live bugs, I personally don't think it matters much.

The big downside I see in the specs for the Pentax-DA 35mm F2.4 AL is the part about "Aperture Ring: No - controlled via camera body". If that's true for the lens that you have, then it seems like a big drawback because you must be either shooting wide open or somehow stopping down with it mounted on a body, and getting the stop to hold when you remove and reverse it. In that one regard, having a lens with a manual aperture would be a lot more convenient.

One more thing, I notice that both of these images seem to have an up-close-and-personal perspective, with for example the abdomen in the background looking a lot smaller then the head in the foreground. That sort of perspective is characteristic of having the entrance pupil be close to the subject. You won't get the same "feel" if you use a longer lens.

Bottom line is that your images here look good to me. My big concerns would be about lack of flexibility in terms of magnification and aperture settings.

But I'm not you. What is it that you care about?

--Rik

Thagomizer
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Post by Thagomizer »

Lou Jost wrote: The projected image on the sensor is usually just a small crop of the whole image projected by the reversed lens or the enlarger lens. The smaller the crop, the greater the drop in resolution (in lp/mm). So for example, if you are using a reversed macro lens that was designed for a 35mm sensor, and you use enough extension to get 2x, you have cropped the aerial image projected by the reversed lens by a factor of 2. So I think the central resolution (in lp/mm) of the projected aerial image should be only about half the central resolution of the image projected at 1x.

Lenses designed for smaller sensors generally have higher resolution (in lp/mm) than lenses designed for larger sensors. This will still be true when reversed. For a given reversed lens (assuming it is not tightly optimized for a single magnification), central resolution should be at its best when the reversed magnification roughly equals the ratio of the camera sensor divided by the film or sensor size the lens was designed to image. So for example, generally a micro-four-thirds lens reversed at 2x (or a little bit more to improve the corners) on a FF camera should do very well, and should have better central resolution than a FF lens reversed at the same magnification. I have tested this using the Nikon 60mm D versus Olympus MFT 60mm lens, and the results confirmed this. I posted this here:
https://www.photomacrography.net/forum/ ... highlight=

In general, a reversed lens should deliver the highest central resolution when the projected image is not cropped. That means that if you use a FF sensor, for 2-3x you should use reversed MFT lenses, or enlarger lenses meant to enlarge smaller negatives; for 1x you should use FF lenses. For higher magnification you should look for lenses designed for even smaller negatives or sensors.
I'd never thought of it this way. That certainly helps explain why I get very good results from the reversed D mount 8mm cine lenses I use on occasion.

rjlittlefield wrote: While I'm prattling on, please be thinking of an answer to this question: What is it about your current images or workflow that you would particularly like to improve?

You've said "single shots", and you've shown us a couple of examples that appear to be around 1:1 or a little higher on an APS-sized sensor (Pentax KP).

I notice that the images have wonderfully smooth bokeh, both in front and behind focus, and I'm not seeing any significant problems with either color fringing (radial CA) or color shifts due to longitudinal CA. Central sharpness looks fine, and there's nothing in focus on the edges/corners to worry about.

When I search on Pentax 35mm f2.4 "plastic fantastic" I get pointed to the Pentax-DA 35mm F2.4 AL, for which there's an extensive review at https://www.pentaxforums.com/reviews/pe ... ction.html . If I'm reading it properly, they're pretty happy with the lens's glass, giving it high marks for sharpness, control of flare, small amount of chromatic aberration ("purple fringing" on a slightly OOF hard edge), and good bokeh with background foliage (despite only 6 straight blades in its aperture).

Granted, their tests were at long distance focus, not 1:1, so it's very likely that the lens picks up some curvature of field and some spherical aberration (loss of contrast for fine detail) due to the close focus. But still, "the proof is in the pudding", and the shots that you've shown look fine to me. Flat fields are important if you're shooting flat subjects, but for live bugs, I personally don't think it matters much.

The big downside I see in the specs for the Pentax-DA 35mm F2.4 AL is the part about "Aperture Ring: No - controlled via camera body". If that's true for the lens that you have, then it seems like a big drawback because you must be either shooting wide open or somehow stopping down with it mounted on a body, and getting the stop to hold when you remove and reverse it. In that one regard, having a lens with a manual aperture would be a lot more convenient.

One more thing, I notice that both of these images seem to have an up-close-and-personal perspective, with for example the abdomen in the background looking a lot smaller then the head in the foreground. That sort of perspective is characteristic of having the entrance pupil be close to the subject. You won't get the same "feel" if you use a longer lens.

Bottom line is that your images here look good to me. My big concerns would be about lack of flexibility in terms of magnification and aperture settings.

But I'm not you. What is it that you care about?

--Rik
My question arose more from curiousity rather than dissatisfaction. I'm always interested in expanding my repertoire and tool kit. Enlarger lenses are a bit of a new area for me. I've got an EL Nikkor 50/28 N that I haven't got around to using much yet. I was wondering how something shorter would compare with the WA SLR lenses I've already got. Figured I'd ask for information and suggestions before spending money! From the sounds of it, and the positive comments on my posted images (thank you!) what I've got right now might be sufficient for my needs; I just need to try all my various lenses out more to get a better idea of what bits to use for which subjects/sizes/ magnifications.

As far as controlling aperture on the Pentax DA 35/2.4, I found Fotodiox adapter originally intended to mount Pentax K-mount lenses on Nikon bodies, with aperture control to adjust the diaphragm on lenses lacking an aperture ring. It looks like this:

Image

Pentax lenses w/o aperture rings snap closed when not mounted on a body, so unless you've got something to keep the aperture open, you're shooting closed down. Not fun. This adapter (once one has removed the optical elements that allow infinity focus in its originally intended usage on a Nikon body) works quite well. It bayonettes onto the lens mount of the reversed lens quite easily and offers a declicked aperture control ring. What the actual aperture selected is anybody's guess, but you can at least open it up or close it down without having to jam something against the aperturture control lever to make it stay put! It's thin enough that it doesn't eat up very much working distance, which can be at a premium with this configuration.

Again, thanks everyone.
Last edited by Thagomizer on Mon Mar 09, 2020 9:16 pm, edited 1 time in total.

rjlittlefield
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Post by rjlittlefield »

Thagomizer wrote:As far as controlling aperture on the Pentax DA 35/2.4, I found Fotodiox adapter originally intended to mount Pentax K-mount lenses on Nikon bodies, with aperture control to adjust the diaphragm on lenses lacking an aperture ring.
Lovely! Sounds to me like you're set.

--Rik

lothman
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Post by lothman »

Lou Jost wrote: In general, a reversed lens should deliver the highest central resolution when the projected image is not cropped. That means that if you use a FF sensor, for 2-3x you should use reversed MFT lenses, or enlarger lenses meant to enlarge smaller negatives; for 1x you should use FF lenses. For higher magnification you should look for lenses designed for even smaller negatives or sensors.
so something like the Schneider Kreuznach Xenoplan should work fine?

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