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04-28-2016, 04:57 PM   #1
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Lens diaphragm actuator broken

Hi everyone,

I just received a used lens ordered from here, but unfortunately it wasn't package too well and arrived with the diaphragm actuator broken off. I had never heard of such a thing before, and am basing that diagnosis based off of a diagram of the Pentax lens mount that I found (attached). Strangely enough, Google does not find anyone with my problem, so I'm at a loss as to the implications of this. I'd really like to be able to use the lens to its full original capacity (manual focus but with A aperture setting) but don't want to test it out by attaching it to my camera lest it cause issues.

Does anyone know if this can be (hopefully easily) fixed? Am I able to make use of this lens?

Thanks in advance.

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04-28-2016, 05:09 PM   #2
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What is the lens? That could help a little bit. Also, some pictures of the lens would help - to better assess the damage sustained.
04-28-2016, 05:28 PM   #3
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Photos attached. I think the narrower end of the silver piece is the side that's supposed to be attached to the lens. On the lens itself it's hard to tell where it broke off, but the narrow slit in the picture is where the piece came from. The lens is a Vivitar Series 1 28-90MM F/2.8-3.5.

---------- Post added 04-28-16 at 05:31 PM ----------

I just realized that it's not the diaphragm actuator, but the stop down indicator that's broken off. In my dismay at finding a broken piece I wasn't looking at the diagram straight... But I think the effect is what I had assumed, which is that the aperture cannot be controlled by the camera now?
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PENTAX K-3  Photo 
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PENTAX K-3  Photo 
04-28-2016, 06:06 PM   #4
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OK - slow down. Film Camera or DSLR? If DSLR and IF that's the part that goes in the slot and does not open the iris up on the lens - then you are completely OK. If the part is still attached to the lens that when you flip it with your finger it opens the blades on the lens you are fine.

If you shoot film - you are not fine - the body reads the position of the aperture using that. It may still work on some bodies correctly in A mode but I'm not sure which.

04-28-2016, 06:25 PM   #5
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DSLR (K-3)! After I read your reply I went ahead and tried attaching it to my camera, and it does look like it's fine! That's a HUGE relief, thank you so much for the reassurance! I have to wonder though, why do even the DA lenses still have the tab?

One question about using the lens though - it's my first zoom manual focus lens (my others are primes), and when I first turn on the camera with it attached it asks me to choose a focal length. The choice is obviously straightforward for a prime, but does it matter that I'd only choose one focal length for a zoom?
04-28-2016, 06:44 PM   #6
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The stop down indicator doesn't matter on K-mount DSLR since it is not used, e.i. the mount is "crippled".
04-28-2016, 06:59 PM   #7
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Yup, nothing to worry about if you only plan to use DSLRs

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04-28-2016, 06:59 PM   #8
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QuoteOriginally posted by Jmhsnk Quote
I have to wonder though, why do even the DA lenses still have the tab?
I'm gobsmacked. I have never looked at the bottom of the DA lenses with that in mind. The DA 15 has it - and it doesn't even have an aperture ring (as most DA's don't). I can only assume is is there to mate with Teleconverters and bellows and even film cameras. Without the slot the camera would not mount the lens. What's a little stranger is that it appears there is something in the slot but maybe it is just there to give the lever in the camera something to mate with.

04-28-2016, 09:14 PM   #9
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The dummy tab is there so if you should mount the lens on a non-crippled mount camera to signal the camera to use stop-down metering. That's why the M42 adapter catches the stop-down signal lever and moves it to a set position.
04-28-2016, 09:17 PM   #10
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QuoteOriginally posted by Not a Number Quote
The dummy tab is there so if you should mount the lens on a non-crippled mount camera to signal the camera to use stop-down metering. That's why the M42 adapter catches the stop-down signal lever and moves it to a set position.
Ah - mystery solved! Thanks.
04-29-2016, 03:45 AM   #11
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Thank you everyone for reassuring and teaching this newbie.

QuoteOriginally posted by UncleVanya Quote
I'm gobsmacked.
What a wonderful phrase that I don't hear very often!
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