Reversed zoom lens technical questions

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Thagomizer
Posts: 71
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

Reversed zoom lens technical questions

Post by Thagomizer »

Hello all;

I've had a lot of fun and good results from using reversed zoom lenses for hand-held macro work in the field. The variable magnification gives me a degree of flexibilty that a reversed prime would not. Here are a couple of shots from a reversed Pentax DA 18-55 II kit zoom.

Image

Image

You can see more of my images from the same lens here: https://www.flickr.com/photos/bruce_woo ... 559819208/


My inspiration for doing this was Johan J Ingles-Le Nobel's "Anybrand MP-E65mm" http://extreme-macro.co.uk/anybrand-mpe-65mm/

One of the lenses I use most frequently for reversed shooting is the above-mentioned Pentax DA 18-55 f3.5-5.6 II. I am wondering, though, would a faster f2.8 18-50 give any better results? They're supposed to be better than a standard kit lens used right way round; would that also be the case when reversed? I've read (but not tested myself) that slower f1.7, f1.8, or f2 50mm lenses work better for reverse macro shooting than fast f1.4 or f1.2 fifties as they exhibit fewer abberations. Would this hold true for faster zoom lenses as well?

One of the ingredients Johan uses in creating his rig is a deglassed 50mm f1.7 http://extreme-macro.co.uk/empty-lens/ lens for automatic aperture. I haven't done this yet myself. Having such an automatic diaphragm would make using the reversed lens a little easier, giving a brighter view for focusing and composition.
The deglassed lens acts as an extension tube with automatic diaphragm and auto aperture control, with the aperture on zoom lens left wide open. My question in this regard is whether the change in position of the diaphragm from the reversed zoom to the deglassed lens/extension tube reduces image quality? With stacked lenses, the preferred aperture to close down is on the reversed shorter focal length lens, rather than the longer lens mounted on the body, (with an aperture placed between the two lenses perhaps being a better option still). For the reversed zoom on deglassed lens, is there a similar optimal position for diaphragm placement for the best image quality? I thought it might be good to find this out before 1) acquiring and 2) disassembling such a lens.

Perhaps I'm foolishly chasing miniscule, barely noticeable improvements in image quality, but if I can eke out a sharper image, why not? I'm guessing I'm not alone in this potentially Quixotic optical quest for more, better and sharper.... :D

Thank you for your attention.

Thagomizer
Posts: 71
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

Re: Reversed zoom lens technical questions

Post by Thagomizer »

Maybe have a look at auto reverse adapters instead? That's a set of two auto extension tubes, connected to each other not by direct contacts but by an extension cord. One tube is mounted to the camera, the other is connected to the lens mount of the reversed lens. This will allow you to control the aperture of the reversed lens from the camera. Plus, there is a thread for a protective filter for the reversed lens. They are sold by Movo, Meike, Novoflex and others.

I read somewhere that you could make your own by soldering the contacts to extension cords ...

The contacts would even allow you autofocus (apparently), but be careful. If the lens has simple front focus, the lens mounted on the filter thread might not be strong enough to move the weight of the whole lens all the time. Best then to set the lens to minimum extension (unually infinity) and switch to manual focus to protect the focussing motor.
Thanks for the suggested solution, but as far as I know, such an accessory is not available from any maker for Pentax cameras and lenses. Except for a very small number of lenses, Pentax AF lenses still use a mechanical aperture control lever to allow the camera body to set the selected f-stop. This would make a reverse adapter for K-mount cameras and lenses much more complicated to make, either commercially, or as a do-it-yourself project. Brands with completely electronic communication between body and lens are much easier to make adapters like this for. Also, given its small sales share, and limited aftermarket lens support, there's not going to be a big enough market for such a product to be viable for the Pentax mount.

Ichthyophthirius
Posts: 1152
Joined: Thu Mar 07, 2013 5:24 am

Re: Reversed zoom lens technical questions

Post by Ichthyophthirius »

Hi,

You're right. I had deleted my post, just before you made your reply, when I realised that was the case.

Now Johan's deglassed lens makes more sense; the simple auto reverse adapter solution for Canon isn't available for Pentax.

My guess is that the aperture of such a deglassed lens is not in an ideal location for a zoom lens (too far away from its normal location).

BTW those images are great.

Thagomizer
Posts: 71
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

Re: Reversed zoom lens technical questions

Post by Thagomizer »

Hi,

You're right. I had deleted my post, just before you made your reply, when I realised that was the case.

Now Johan's deglassed lens makes more sense; the simple auto reverse adapter solution for Canon isn't available for Pentax.

My guess is that the aperture of such a deglassed lens is not in an ideal location for a zoom lens (too far away from its normal location).

BTW those images are great.
I was wondering where the post went!

Thanks for replying anyhow; I'd mentioned a Pentax lens, but hadn't indicated that the body I shoot with is also Pentax, so no problem. I've rather thought myself that the empty lens aperture position might have a cost in image quality, though judging from Johan's results, it's probably not much. I've lived without automatic diaphragm this far, so continuing to do so isn't really a hardship. (Thank you for your kind words about my images. When things work out, I really like my results. I'm glad you like them too.)

I know chasing "better" is probably silly, but I could find something better just by messing around. I'm not above silly. :D

Thinking out loud. Another option I might try is to deglass a surplus Vivitar 2X Macro Focusing Teleconverter to turn it into a helicoid. Mounting a reversed prime on this would give me the variable magnification I get with my zoom, with (perhaps) better image quality from the prime lens. Still no auto diaphragm, but maybe better IQ than the kit lens or even an f2.8 17-50 (which would be bigger and heavier than any prime I would be using.) It's also cheaper to use stuff I've already got: if I talk myself out of buying more stuff, then go me!

Ichthyophthirius
Posts: 1152
Joined: Thu Mar 07, 2013 5:24 am

Re: Reversed zoom lens technical questions

Post by Ichthyophthirius »

Thagomizer wrote:
Mon Sep 07, 2020 12:44 pm
I know chasing "better" is probably silly,
Ultimately, you would get the best if you shoot with a large aperture (just stopped down far enough to suppress spherical aberration) and then do focus stacking, if your subject is suitable for stacking.


I'm also interested in an answer to your other initial question; if there is a difference when using a reversed 50mm f/1.8 vs. 1.4 or 1.2!

Thagomizer
Posts: 71
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

Re: Reversed zoom lens technical questions

Post by Thagomizer »

Ultimately, you would get the best if you shoot with a large aperture (just stopped down far enough to suppress spherical aberration) and then do focus stacking, if your subject is suitable for stacking.


I'm also interested in an answer to your other initial question; if there is a difference when using a reversed 50mm f/1.8 vs. 1.4 or 1.2!
I usually do handheld single shot stuff in the field. I haven't tried stacking yet; I suspect my computer would freeze up choke to death if tried putting that many pixels through it.

As for the differences between fast 50s and slower ones, I might have misapplied something I read in Lefkowitz https://www.amazon.com/Manual-Close-up- ... 0817421300 about extension and applied it to reversal. Whether a faster, higher quality f2.8 18-ish to 50-ish zoom would be any better than the vanilla kit lens I'm using now remains an open question.

clarnibass
Posts: 130
Joined: Fri Jun 10, 2016 11:33 pm

Re: Reversed zoom lens technical questions

Post by clarnibass »

A larger aperture lens could be better if diffraction is an issue with your current setup...? At the cost of DOF. I guess it depends on the magnification and aperture you're using now.

Re using different reversed lenses in general, it can definitely make a difference. I've only made one comparison, but results with a reversed Nikon 55mm Micro were significantly better than a Nikon 18-55mm lens at 55mm. The zoom has a minimum aperture of f/5.6 and if I remember, I used to use either f/4 or f/5.6 on the lens for that setup (the reversed 55mm was my x2 setup for a while). I've only tried this coupled with another lens, not with just extension tubes, but I imagine that shouldn't make a difference. The 55mm Micro was also very noticeably better when compared normally.

For normal online FHD (no 4K) size screen sizes... not sure if I could tell a difference. I printed up to about A2 back then and that showed the difference easily when looking from a close distance.

That's pretty much all my experience with comparing different reversed lenses.

Thagomizer
Posts: 71
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

Re: Reversed zoom lens technical questions

Post by Thagomizer »

clarnibass wrote:
Sat Sep 12, 2020 6:14 am
A larger aperture lens could be better if diffraction is an issue with your current setup...? At the cost of DOF. I guess it depends on the magnification and aperture you're using now.

Re using different reversed lenses in general, it can definitely make a difference. I've only made one comparison, but results with a reversed Nikon 55mm Micro were significantly better than a Nikon 18-55mm lens at 55mm. The zoom has a minimum aperture of f/5.6 and if I remember, I used to use either f/4 or f/5.6 on the lens for that setup (the reversed 55mm was my x2 setup for a while). I've only tried this coupled with another lens, not with just extension tubes, but I imagine that shouldn't make a difference. The 55mm Micro was also very noticeably better when compared normally.

For normal online FHD (no 4K) size screen sizes... not sure if I could tell a difference. I printed up to about A2 back then and that showed the difference easily when looking from a close distance.

That's pretty much all my experience with comparing different reversed lenses.
Thanks for your reply. More often than not I'm using the reversed kit lens in the 24-18 range. Maximum aperture is f3.5, but I do close it down a bit. I use a deglassed Fotodiox aperture control PK-Nikon F adapter on the mount end of the lens for closing it down, but there's no f value given, it's just larger or smaller lens opening. I usually have it somewhere in the middle; I haven't done enough tests or comparisons to see where diffraction becomes objectionable. I do have 35, 28 and 24mm primes that I could work with, but the flexibility of the zoom and its variable magnification is hard to give up.

clarnibass
Posts: 130
Joined: Fri Jun 10, 2016 11:33 pm

Re: Reversed zoom lens technical questions

Post by clarnibass »

I definitely wouldn't get one of those (very?) expensive f/2.8 zooms with just the hope that it would be better. I would want to compare the specific lenses in a way that is meaningful to how I use them. For example, it's only when I printed at about A2 size that I noticed an issue with my extension tube setup, and changed to a coupled reversed lens (much better, huge difference). For online photos both were fine, small but not very significant difference.

I would probably first do some basic test with your zoom and primes to see if there's a difference that is significant for you.

Thagomizer
Posts: 71
Joined: Fri Jan 25, 2019 2:24 pm
Location: London Ontario

Re: Reversed zoom lens technical questions

Post by Thagomizer »

clarnibass wrote:
Sat Sep 12, 2020 9:12 pm
I definitely wouldn't get one of those (very?) expensive f/2.8 zooms with just the hope that it would be better. I would want to compare the specific lenses in a way that is meaningful to how I use them. For example, it's only when I printed at about A2 size that I noticed an issue with my extension tube setup, and changed to a coupled reversed lens (much better, huge difference). For online photos both were fine, small but not very significant difference.

I would probably first do some basic test with your zoom and primes to see if there's a difference that is significant for you.
Good advice! I've got all sorts of combinations for macro, really don't need to go looking for more. I've got enough to keep me busy for a long time...

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