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03-14-2019, 12:36 AM   #496
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Can anyone tell me how to use newer lenses in reverse? I recently got a 21mm LTD which I'd like to use with my 200mm instead of my pentax-M 28mm/3.5 (that combination works great btw), but the lack of apperture ring doesnt help. Does anyone know any tricks to get the 21mm to keep a certain aperture when used in reverse?

03-14-2019, 02:14 AM   #497
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I have found a particular web page that deals with your issue. Quote from that page:-
"There is a way to manually change the aperture on a lens without an aperture ring – this requires mounting the lens to the camera for normal shooting (i.e. not reversed), setting the desired aperture in manual mode, holding down the DOF preview button while removing the lens from the camera"

Shooting Insect Macros on the Cheap with a Reversed Lens

I have also noticed that I may have been doing all this wrong.. I have gone about setting up an enlarger lens in front of another lens... No reversal needed for just under 2:1.
I have achieved 1.9583:1 by getting a comparon 105mm onto a Pentax-A 80-200 lens.
I have posted the details in this forum here.

I will now setup for this on a reversed lens and see what I get.

Last edited by VILLAINofOZ; 03-14-2019 at 03:23 AM. Reason: More too add.
03-14-2019, 05:07 AM   #498
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QuoteOriginally posted by xandos Quote
Can anyone tell me how to use newer lenses in reverse? I recently got a 21mm LTD which I'd like to use with my 200mm instead of my pentax-M 28mm/3.5 (that combination works great btw), but the lack of apperture ring doesnt help. Does anyone know any tricks to get the 21mm to keep a certain aperture when used in reverse?
As far as I know there isn't a good work around for this problem. One can use gaffers tape to hold the lever once the desired aperture is set manually.

But that is kind of a Rube Goldberg solution. Not really a good solution.


This is why I avoid lenses without aperture rings.
03-14-2019, 07:40 AM - 4 Likes   #499
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QuoteOriginally posted by xandos Quote
Can anyone tell me how to use newer lenses in reverse? I recently got a 21mm LTD which I'd like to use with my 200mm instead of my pentax-M 28mm/3.5 (that combination works great btw), but the lack of apperture ring doesnt help. Does anyone know any tricks to get the 21mm to keep a certain aperture when used in reverse?
I picked up one of these recently:

Pentax K AF Mount (PKAF) DSLR Lens to Nikon F Mount SLR Camera Body Adapter ? Fotodiox, Inc. USA

Its original purpose was to enable the mounting of PK mount lenses on Nikon F mount bodies. It has aperture adjustment capability for lenses without aperture rings, like your 21 LTD. I removed the optical elements designed to allow infinity focus in its intended use and mounted it on the forward facing lens mount of my reverse mounted 18-55 kit zoom. It works great for aperture control, much better than my previous solution of jamming something to keep the aperture tab open! It's a de-clicked ring that allows varying degrees of opening or closure. What aperture you've got is a matter of guesswork, but it does work to keep the aperture open at a fixed position.

Things are just starting to thaw out here, so I'll be using it soon for closeups of bugs and buds.

I'd be very curious to see your 21 LTD's results. I get quite pleasing results from a reversed kit lens, so the LTD would be better, I imagine.

Here are some shots I got using my Sigma 10-20 reversed, at 10mm. Please excuse the dirty sensor! Field of view here is about 4mm, so this is almost 6x. Your 21 reversed should give you nearly 3x.





03-14-2019, 08:27 AM   #500
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QuoteOriginally posted by Thagomizer Quote
I picked up one of these recently:

Pentax K AF Mount (PKAF) DSLR Lens to Nikon F Mount SLR Camera Body Adapter ? Fotodiox, Inc. USA

Its original purpose was to enable the mounting of PK mount lenses on Nikon F mount bodies. It has aperture adjustment capability for lenses without aperture rings, like your 21 LTD. I removed the optical elements designed to allow infinity focus in its intended use and mounted it on the forward facing lens mount of my reverse mounted 18-55 kit zoom. It works great for aperture control, much better than my previous solution of jamming something to keep the aperture tab open! It's a de-clicked ring that allows varying degrees of opening or closure. What aperture you've got is a matter of guesswork, but it does work to keep the aperture open at a fixed position.
I remember seeing that post, but had forgotten it.

Looks like a great workaround.

Much better than cramming a toothpick between the aperture control lever and the lens body.
03-14-2019, 07:58 PM   #501
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Thanks for the very quick replies! I avoided getting the 21LTD for a long time for its lack of aperture ring (and incompatibility with FF for when I cave and get a K-1), but I ended up putting in a lowball bid and getting it for way under the price I could get a pentax-M 20mm/4 for, I guess I cannot complain! Although the lens rattles, something is loose inside. Very disconcerting. But it shoots just fine.

I tried the thing with the DoF preview while dismounting the lens. That definitely does not work for me. I'll look into the fotodiox mount, that would probably do the trick! I've been trying to hold the aperture lever in place by hand, but its tricky. I use the 21mm reverse/mounted on a 200mm, so I can have no vibrations at all, and exposure times are often about a second.

I got pretty decent results recently with a 28mm/200mm. I am still hesitating if I can post them here, they are work-related designs, so its a bit iffy. But I can definitely resolve structures smaller than 5um, so I am pretty happy. The reversed 21mm instead of the 28 should give me a decent extra bump in magnification, if its similarly sharp. The M28/3.5 is quite good at this kind of stuff.
03-14-2019, 11:53 PM   #502
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The pixel pitch of the kp is 3.3um. Can't do much more with current tech. You are resolving at the pixel level.
03-15-2019, 02:23 AM   #503
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I can't say I agree with that logic. Diffraction and light wavelength limits what we can resolve eventually, but I can take a camera with a pixel pitch of 50um, hook it up to a microscope and resolve details way beyond 50um. That is what the magnification is for. My setup should give me a magnification factor of about 7 (more with the 21mm), so I'm not limited by pixel pitch yet. And if I were, I could still increase the magnification factor of the setup. In other words, pixel pitch doesnt set a limit on resolving power if you play with optics.

03-15-2019, 04:44 AM   #504
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QuoteOriginally posted by VILLAINofOZ Quote
I have found a particular web page that deals with your issue. Quote from that page:-
"There is a way to manually change the aperture on a lens without an aperture ring – this requires mounting the lens to the camera for normal shooting (i.e. not reversed), setting the desired aperture in manual mode, holding down the DOF preview button while removing the lens from the camera"
There is no way this will work.

The aperture mechanism is spring loaded to return to fully open once the lever is released. As soon as the lens is removed from the camera, the lever is no longer being held in place by the camera, or any other means.

The part of the mechanism on the camera side of the mount doesn't come off with the lens, so what can be holding the last aperture setting against the force of the spring?
03-15-2019, 05:51 AM   #505
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Xandos,
I was thinking in 1:1 terms. Then that 3.3 um represents 3.3um. Of course at 2:1 2 pixels will represent 3.3um. The true macro threshold confuses me all the time.
03-15-2019, 03:29 PM - 1 Like   #506
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QuoteOriginally posted by Racer X 69 Quote
There is no way this will work.

The aperture mechanism is spring loaded to return to fully open once the lever is released. As soon as the lens is removed from the camera, the lever is no longer being held in place by the camera, or any other means.

The part of the mechanism on the camera side of the mount doesn't come off with the lens, so what can be holding the last aperture setting against the force of the spring?
I've never tried it so I don't know, but I believe this method does work for Canon EOS lenses, which have only electrical contacts and no aperture control tab. The purely electronic approach allows Canon shooters to use one of these to get automatic diaphragm when using reversed Canon autofocus lenses.

Unless I'm mistaken the KAF4 mount, so far used only on the 55-300 PLM, could be linked to camera controls in a similar way when reversed. Interesting....
03-15-2019, 06:46 PM   #507
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QuoteOriginally posted by Thagomizer Quote
I've never tried it so I don't know, but I believe this method does work for Canon EOS lenses, which have only electrical contacts and no aperture control tab. The purely electronic approach allows Canon shooters to use one of these to get automatic diaphragm when using reversed Canon autofocus lenses.

Unless I'm mistaken the KAF4 mount, so far used only on the 55-300 PLM, could be linked to camera controls in a similar way when reversed. Interesting....
Well that makes sense, good point. I can see how the aperture would stay put if it is being moved by a stepper motor.
03-27-2019, 06:38 AM - 1 Like   #508
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Medium format BK

A few macro shots with the K-1 and Mamiya C 80mm f 4.0 macro. Used with an adapter, this well-made medium format Mamiya lens is an interesting macro possibility for Pentax users. As used here, this lens offers 1:2 macro capability, but there is a spacer available that takes the lens to 1:1. The lens is also an excellent landscape and portrait lens, though maybe a little sharper than some subjects might appreciate in portraiture use.
Attached Images
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Last edited by ivanvernon; 03-27-2019 at 06:39 AM. Reason: Spelling correction.
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