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06-18-2015, 06:16 AM   #1
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A28 contact does not lift up

Hi

I have an A28 and the lens contact does not lift up above the lip the of the lens casing. As such when I fit the lens on my K5 it does not connect to the camera and as such does not give an aperture value when the lens is set to A. I can push the contact down and it pushes back up again but does not raise above the lip of the lens. I've pushed it down many times with the hope that it will lift up all the way but this hasn't happened.

Any ideas on how I can get the contact to lift up fully without dismantling the lens?

Any ideas will be greatly appreciated.

06-18-2015, 06:53 AM   #2
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I can't see how you'd fix that without removing the mount.
06-18-2015, 06:54 AM   #3
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Is the aperture ring locked in the A position? I know this sounds obvious, but it is not uncommon for users to put the ring at f/22 without depressing the small button allowing it to move completely to the A position.


Steve
06-18-2015, 07:28 AM   #4
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QuoteOriginally posted by stevebrot Quote
but it is not uncommon for users to put the ring at f/22 without depressing the small button allowing it to move completely to the A position.
That would be my first thought.

If the pin mechanism is the same as on the 50mm f/1.7 then the pin itself is spring loaded. The pin assembly is lifted or pushed into the raised position by a slot on the ring and a tab on the pin assembly.

So some of the ways this can fail are:
  • the opening for the pin is blocked
  • the slot or tab is worn
  • the ring is not seated properly so the tab and slot don't align in the "A" position
  • the "A" setting button is blocked so "A" mode cannot be set or switched out of*
*this is a common problem with the 50mm f/1.7 as the spring clips for the "A" button often break loose.

If the mechanism is the same as the 50mm f/1.7 then accessing the "A" pin mechanism is rather simple - it involves removing the K-mount bayonet, a ring or two and perhaps the aperture ring. The "A" assembly is 3 or 4 very tiny parts and there is a spring and ball bearing that are easily lost for the aperture ring.

It could just be a matter of adding some grease to the tab and slot on the aperture ring. If it is like the 50mm, then this can be done without removing the aperture ring and risk losing the ball bearing or having to fiddle around with put it back together.

https://www.pentaxforums.com/forums/114-maintenance-repair-articles/88051-pen...ng-repair.html

06-18-2015, 07:32 AM   #5
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It can usually be done without removing the aperture ring. I tape the aperture ring to the rest of the lens with painters tape any time I remove a mount to avoid the whole lost ball bearing thing. The A pin will have a very tiny spring though that you have to watch out for. If it is really not working (in true 'A' position) then it probably got that way from previous service -- often just needs to be bent up ever so slightly...
06-18-2015, 08:52 AM   #6
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Thanks everyone

Thanks everyone for your suggestions. The first thing I tried was to make sure that I actually had the aperture ring set at A.

I found that it was at 22. A quick press of the button and the ring slipped into the A position. I mounted the lens on my camera and all works as it should.

I also have the A50 1.7 and never had a problem with it, just this time I must have not put the 28 back into A properly.

I really appreciate all of your responses. Thank you very much everyone.
06-18-2015, 09:21 AM   #7
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QuoteOriginally posted by FreeSpirit9 Quote
I found that it was at 22. A quick press of the button and the ring slipped into the A position. I mounted the lens on my camera and all works as it should.
Ta! Da!

Glad this worked for you


Steve
06-18-2015, 09:45 AM   #8
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Glad it was something as simple as that. The "A" button seems to be in a natural place for my thumb and many times I find myself setting it in the "A" mode when I want it in manual.

06-18-2015, 10:35 AM   #9
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I'm really glad it was that. I was not even looking to forward to contemplating dismantling the lens.

Thanks again.

Cheers
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