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11-20-2015, 05:51 AM   #1
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No Aperture control on RMC Tokina 28mm 2.8

I could shoot some very nice pictures with this lense wide open.

The lens just seems not to stop down, no matter how I turn the aperture ring.

Do you have any advice on this?

11-20-2015, 06:32 AM   #2
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https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/110658-u...x-dslrs-f.html
11-20-2015, 08:43 AM   #3
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Are you talking about it not stopping down ON the camera or OFF the camera? If it's not stopping down off the camera, it needs repair at once.

If it's not stopping down ON the camera, and you've followed all the advice in Boriscleto's link, the other thing you may need to bear in mind is this - lenses which have anodised mounts (black colour like the rest of the lens surface, rather than silvery bare metal) won't work on these cameras because the contacts aren't grounded (it matters for some reason). Get a piece of conductive electrician's tape and apply it to the rear rim of the lens where the contacts touch. That should solve your problem; it solved mine with an old Vivitar 28/2.8 which for all I know is a rebranded version of your lens.
11-20-2015, 10:19 AM   #4
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QuoteOriginally posted by pmeier Quote
I could shoot some very nice pictures with this lense wide open.

The lens just seems not to stop down, no matter how I turn the aperture ring.

Do you have any advice on this?
Welcome to the Pentax Forums!

Advice? Right here!:
  • Confirm that you are shooting in M mode. Your camera will not stop down a non-A contact lens in any of the automated exposure modes. X mode should work too if you are shooting flash.
  • Confirm that the aperture on your lens is functioning properly. You do that by taking the lens off the camera and flicking the aperture actuator lever on the back of the lens. The aperture should close and open with a snappy action at all settings short of full open.
As for non-conductive (painted) mount surfaces, whether it is a problem depends on which body you are using. The issues include failure of catch-in-focus and green button not working as expected in M mode. I am don't remember failure to stop down being a problem with any of those lenses, though I have been wrong before


Steve


Last edited by stevebrot; 11-20-2015 at 10:52 AM.
11-21-2015, 12:32 AM   #5
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Thanks for all the valuable advice!

The lens is mounted to a Sony mirrorless with an adapter and i shoot in 'M' mode. The adapter works well on other lenses and it does not have any contacts on it.

Off camera, the lens is not working properly. Turning the aperture ring on either side does not change anything on the blades - it stays always wide open.
Also moving the black stick on the back does not impact the blades either.

It's a pity. The reviews on this lens are very good but i think it's not worth a repair.

peter
11-21-2015, 12:50 AM   #6
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I've had a couple of Vivitar zooms do this. One was oil on the blades, easily fixed and it got a general CLA at the same time. The other is still in for diagnosis and repair, but I suspect it will turn out to be the same problem.

Did your lens ever work, or is this how it came to you?
11-22-2015, 02:16 AM   #7
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I bought the lens as is for pretty cheap on a local flea market without checking the aperture ring.

So, learned to check that for future acquisitions.

As for your zoom, did you fix it yourself or to a local store?
11-22-2015, 05:52 AM   #8
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I sent mine to PhotoTec Services in St John's, Newfoundland.

There should be at least one guide on the forum here of things to check for when buying a lens in person. Alternatively if YouTube is your thing, "the angry photographer" and a chap called David Hancock both have good advice on how to assess a lens.

When buying them in person, the best thing is to take a DSLR with you, and after you've given it a general look-over, mount the lens and take a series of pictures with it. That will enable you to test whether things like aperture control and autofocus are working correctly, and whether the lens takes decent pictures. Depending on the circumstances you may or may not have the opportunity to go away and look at the pictures on a decent sized screen, but if you do, you should take it (a laptop and a nearby coffee shop are good for this if available). If not, you just have to look at the pics on the camera's own screen at max zoom and look for any obvious flaws. This is far from optimum, but far better than nothing.

The other thing to remember is that if manual focus is your thing, M42 glass is not to be sneezed at. Get thyself an M42/K (or whatever your mount is) adapter with infinity focus and make sure you have it with you when you go lens browsing.


Last edited by pathdoc; 11-22-2015 at 05:59 AM.
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