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I recently brought a Rokinon 135 mm f/2 lens for my Nikon D5000 from Amazon.

This lens is designed for Nikon cameras and the way it's supposed to work is when you mount it, you have to set the aperture ring on the lens to f/22 and then you're able to set the aperture of the lens from the camera itself.

As expected, at first, when I mount the lens, it asks me to set the blades to f/22. But strangely, once I do that, I'm not able to set the aperture from the camera. The camera says it's changing, but the blades don't physically move and I've even tested while taking a picture. Regardless of what I set the aperture to be on the camera, the blades move to the same location, about f/5.6, when I click the shutter. I tested this by taking a 2 second exposure so I could clearly see it.

I noticed another strange behavior after closely investigating this: as I mount the lens, the more I engage the bayonet, the wider the minimum aperture becomes. I mounted it while the aperture ring on the lens was at f/22, and the more I engaged the bayonet, the wider it became, even though I wasn't touching the aperture ring and I verified that I was not moving it.

Should I return this lens? Is it faulty? Or am I missing something about the way the Nikon camera works with these lenses?

For now my temporary solution is to not fully engage the bayonet and to manually change the aperture using the aperture ring on the lens. It's relatively stable this way, however I don't like this and would appreciate a long term solution.

One additional point of information: the camera is relatively old and sometimes, with kit lenses, it gives an error in the camera shutter, which I resolve by taking the lens off and shooting a picture without any lens. A similar thing happened while I was testing the Rokinon lens, so I suspect it has something to do with the AE chip that communicates with the camera.


As described in this comment here is the results of that experiment.

This image was at f/2, ISO 1000, with shutter speed of 1/200.
Test image at f/2, ISO 1000, 1/200

This image was at f/11, ISO 1000, with the same shutter speed
Test image at f/11, ISO 1000, 1/200

This image was at f/22, ISO 1000, with the same shutter speed
Test image at f/22, ISO 1000, 1/200

As you can see there is a difference in their brightness, yet I would expect a much greater difference. For experiments sake, I slightly unscrewed the lens so that the AE chip wouldn't make contact, and indeed, when setting the aperture manually via the aperture ring, the difference between f/2, f/11 and f/22 is much more significant than in these images.


As requested, pictures of the aperture lever.

enter image description here enter image description here

Basically my aperture lever isn't behaving as according to Steven Kersting's answer, it's spring-loaded but doesn't move freely through what I assume it should move through (see pictures). I can only move it like a millimeter at most, and its resting position is not at the top of the little gap, which would make sense.

My lens's "resting position" is around f/5.6 which seems to correspond to the aperture levers resting position.

Additionally this might explain why only my kit lenses cause my camera to give a shutter error. If I use a lens that doesn't communicate with my Nikon I get no such error.

Thanks for all the help, I really appreciate it :)

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  • \$\begingroup\$ A better way to tell if a lens is stopping down correctly is to look at the exposure of the resulting images, rather than trying to guesstimate the aperture by looking at the diaphragm blades during exposure. \$\endgroup\$
    – osullic
    Commented Jan 1 at 22:52
  • \$\begingroup\$ Do you know anyone else with a Nikon DSLR that can test your lens on their body? This seems to me to almost certainly be an issue with your camera's aperture lever, not with the lens. \$\endgroup\$
    – Michael C
    Commented Jan 23 at 0:06

3 Answers 3

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I'm only seeing about 0.5 stop difference between the f/2 and f/22 test images; there should be over 3 stops difference.

My best guess is that the aperture lever on the camera body is bent or jammed; and that could be what was causing intermittent errors previously.

It is not terribly uncommon for this to happen if a lens is mounted incorrectly or from some other damage.

This is a picture of a damaged aperture lever: enter image description here

This is what it should look like: enter image description here

And it should move without a lot of resistance (spring loaded to the top). If it is bent and jammed it is possible to bend it back into place. If it is not bent then the body likely needs replaced (factory service uneconomical).

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  • \$\begingroup\$ Thank you for the answer, mine doesn't appear to be damaged but it also doesn't move much. I can nudge it a little bit, though and it does seem to be spring loaded. There's a little gap for the aperture lever on the camera body, it doesn't move through the entire gap and its resting place is a little down from the top. I'll edit my question to include a picture of that. \$\endgroup\$
    – 10 Rep
    Commented Jan 2 at 16:31
  • \$\begingroup\$ My only worry is that this DSLR is very old, about 10 years or so, but I'll see if there are good repair options. \$\endgroup\$
    – 10 Rep
    Commented Jan 2 at 16:31
  • \$\begingroup\$ Please check the question for the pictures of the lever. In the pictures I uploaded its resting position is different from the position shown in your images, and it doesn't move freely as you described. \$\endgroup\$
    – 10 Rep
    Commented Jan 2 at 16:43
  • \$\begingroup\$ @10Rep; that doesn't look right. If it can't be moved to the bottom without much force, and it doesn't return to the top on it's own, then it is almost certainly faulty. Which could explain the occasional errors you've been having that required removing the lens and resetting the shutter. Based upon the cost of a good condition used D5000, I would not send it in for servicing. If this is the correct answer, please mark it as such. \$\endgroup\$ Commented Jan 2 at 17:43
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    \$\begingroup\$ Yeah, perhaps you're right, but I just spent all my saved money on the rokinon lens. Although I am happy that the rokinon seems to be working fine. I'll see what I can do. I would accept your answer but scotbb's answer also covers some good details on how the lens and similar lenses work. I'll accept yours for now since it seems to also cover a problem that others may have. Thank you for the help! \$\endgroup\$
    – 10 Rep
    Commented Jan 3 at 0:02
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You won't see the aperture change until a picture is taken. Because the camera uses through-the-lens metering, the camera keeps the aperture at a wide aperture setting (usually the widest possible). This allows the most light into the lens for more accurate metering.

Additionally, the shallower depth of field with a wide aperture helps the autofocus achieve sharper focus, because areas in in front of or behind the plane of focus fall out of focus much quicker with a wide aperture.

When you press the shutter button, the aperture iris will close down to the determined or chosen value, and then the shutter will actuate and capture the image. After the shutter closes, the aperture resets back to the widest setting.

I noticed another strange behavior after closely investigating this: as I screw the lens on, the further I screw it on, the wider the minimum aperture becomes. I screwed it on while the aperture ring on the lens was at f/22, and the more I screwed it on the wider it became even though I wasn't touching the aperture ring and I verified that I was not moving it.

This is expected behavior. The aperture lever on the lens is spring-loaded, and rests against the aperture control linkage on the camera. The default position of the aperture iris (when the lens is not attached to the camera) is to be as small as the aperture setting on the aperture control ring, or for electronic lenses without an aperture control ring, the smallest possible aperture. As the lens is rotated into its secured, affixed position in the bayonet mount, the aperture is being opened up to the (usually widest) aperture that the camera uses to meter and autofocus.

The camera says its changing but the blades don't physically move and I've even tested while taking a picture.

No, it doesn't say it's changing the aperture size. The camera is noting your commanded (or the program-chosen) aperture setting, and the exposure meter is adjusting its reported value according to the aperture it will use during capturing the image, not during composition.

Regardless of what I set the aperture to be on the camera, the blades move to the same location, about f/5.6, when I click the shutter. I tested this by taking a 2 second exposure so I could clearly see it.

I believe the aperture should open up to the lens's widest setting (f/2 in your case); but it is possible the D500, or conditions that it is being used in, only open up the exposure to f/5.6. But I wonder, how sure are you it's f/5.6 and not f/2?

If the camera is trying to open the lens to f/2 during composition and metering, but the lens only goes to f/5.6, then there might be something wrong with the lens. However, everything else in your question is expected behavior; it is merely a misunderstanding of how the physical aperture linkage system works on the Nikon F-mount bodies and lenses.

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  • \$\begingroup\$ Okay, I understand what you're saying, so I conducted the following experiment: I took 3 different shots with the same settings besides the aperture. One was wide open at f/2, the other at f/11 and the final at f/22. The f/11 and f/22 were respectively darker and the histograms matched that behavior as well yet the light falloff was not that great. I would expect a much bigger difference. I can edit my question to include the three images if needed. \$\endgroup\$
    – 10 Rep
    Commented Jan 2 at 0:47
  • \$\begingroup\$ "After the shutter closes, the aperture resets back to the widest setting." I took the lens off and noted how wide f/2 is visually, but the camera doesn't reset to that. It may not be f/5.6 but I can say with almost full certainty its slower than f/2. \$\endgroup\$
    – 10 Rep
    Commented Jan 2 at 0:48
  • \$\begingroup\$ I think the only strange behavior my lens is exhibiting, after reading your answer, is the fact that when I screw it on to the nikon d5000 with the aperture ring set to f/22, it doesn't open fully and only opens partially. \$\endgroup\$
    – 10 Rep
    Commented Jan 2 at 0:51
  • \$\begingroup\$ @10Rep what happens if you "exercise" the aperture dial all the way over to f/2 and then back to f/22, and then snap through some images? Does the aperture open all the way up? That is, is it possible the aperture iris is just sticking a bit? \$\endgroup\$
    – scottbb
    Commented Jan 2 at 2:31
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    \$\begingroup\$ the aperture linkage is smooth and goes through the full range. I'm not sure what you mean by "snap through some images" but what I did was attach the lens, go to f22, alternate between f2 and f22 with the ring and then shoot some images and the behavior of the lens remained the same. I don't think the aperture iris is just sticking, but what I'll do is find a lens servicer or something and hopefully get a solution. I suspect it has something to do with my camera, can't lie. \$\endgroup\$
    – 10 Rep
    Commented Jan 2 at 5:14
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A long time ago, when photographers measured the light and figured out the aperture and shutter speed required, the aperture on the lens would be (physically) stopped down as necessary, and the shutter set to the required speed. This wasn't ideal because the view through the lens became very dim, making final composition/focusing (and ultimately TTL metering) more difficult.

One of the first automations that appeared in camera/lens setups was "auto-aperture". (Not to be confused with auto-exposure which came later.) Auto-aperture capabilities meant that the required aperture setting could be set on the lens, but the diaphragm itself wouldn't physically stop down until the moment of exposure.

It sounds like you are expecting the lens to behave in the very old fashion of the diaphragm blades reacting immediately to the aperture you set on the lens. That's not how this lens works.

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  • \$\begingroup\$ Yeah, you're right, though I wish it would work like that. I'm using this lens primarily for its f/2 capabilities at 135 mm (effectively 212 for me due to crop sensor) and for me its a little bit of a complication. \ \$\endgroup\$
    – 10 Rep
    Commented Jan 2 at 0:49
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    \$\begingroup\$ @10Rep Why is TTL wide-open exposure metering causing complications? That's how all DSLRs work. It should only be an issue if the lens or camera body isn't functioning correctly (likely the lens) \$\endgroup\$
    – scottbb
    Commented Jan 2 at 2:28
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    \$\begingroup\$ @scottbb This seems to me more like the camera's stop down lever isn't working correctly? But what do I know? I've been shooting exclusively with electronically controlled lens apertures since the mid-1990s? :-) \$\endgroup\$
    – Michael C
    Commented Jan 23 at 0:09
  • \$\begingroup\$ @MichaelC Nobody likes a braggart, lol 😜 j/k. Yeah, after my comment, it became clear that OP's stop down linkage isn't working correctly \$\endgroup\$
    – scottbb
    Commented Jan 23 at 17:27
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    \$\begingroup\$ @scottbb I got it to a repair shop and indeed that was the issue. \$\endgroup\$
    – 10 Rep
    Commented Feb 11 at 3:53

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