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06-19-2009, 08:47 AM   #1
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Taking a lens apart

I have a zoom lens, that does not seem to work on my autofocus cameras. One problem I see is, the aperture does not turn all the way to the "A" position and I was fiddling with it last night. I took the kmount off, then looked inside. Not really knowing what I should be seeing, what was wrong or what I could change, I am asking here. Is there anything I should or could do?

06-19-2009, 09:18 AM   #2
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this might be a really stupid question but......

did yoou push the A button when you turned the ring.

these are usually mechanically interlocked so that you don;t enter and exit the A mode by accident.

there may be nothing at all wrong with the lens.
06-19-2009, 09:33 AM   #3
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Yes, that was a really stupid question. I know enough about lenses to know that A setting is locked to it doesn't shift when shooting. And there is something wrong with the lens because using it on my two cameras that are in my sig, this lens when pushing that button and turning the aperture ring, only goes as far as f22, thus shows as underexposed and refuses to move off that, at any aperture or shutter speed setting.
06-19-2009, 10:15 AM   #4
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QuoteOriginally posted by photolady Quote
Yes, that was a really stupid question. I know enough about lenses to know that A setting is locked to it doesn't shift when shooting. And there is something wrong with the lens because using it on my two cameras that are in my sig, this lens when pushing that button and turning the aperture ring, only goes as far as f22, thus shows as underexposed and refuses to move off that, at any aperture or shutter speed setting.
As I said, I knew it was a dumb question, and no offence intended but I generally try to look for simple answers first.

Now to the real problem.

It sounds as if the button itself is defective, as this is what stops the rotation past F22 to the A setting.

The button probably pushes on a leaf spring, or springy metal piece that has a tip on it, that hits a shoulder or bump on the inside of the aperture ring. I suggest a single bump because the tip will hit the bump and prevent rotation to the A position until the button is pushed, and once over the bump you need to push the button to get it back out of A.

If this piece is damaged, or perhaps bent a little from someone trying to force it perhaps the button cannot make contac any more to lift the tip.

If you show a photo of the lens with the mount removed perhaps I can identify which part to either fix, or remove (if you don't care about the A position ebing lockable,

06-19-2009, 10:51 AM   #5
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he was trying to help you not insult you geez.....
06-19-2009, 11:56 AM   #6
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This is the typical Pentax method of creating a mechanical interlock for the A button. The aperture ring has been removed here.



Other manufacturers will be different. The other critical component of an A lens is an electrical contact between the A pin on the mount and somewhere on the lens itself. Pentax lenses often have a tiny brass spring for this. It wasn't your problem, but make sure it's not missing when you put things together again.

Often there is a small ball bearing trapped between the ring and the barrel to make the ring click at each stop. Make sure this part doesn't spring away. Variable aperture zooms will have even more tiny springs and electrical parts to keep track of.
06-19-2009, 11:59 AM   #7
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dave

this gives a good indication for photolady.

If it were me, I would simply take the two mechanical interlocks away, by removing the screws that hold them in place.
06-19-2009, 01:05 PM   #8
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NO IT WAS NOT A STUPID QUESTION! You were rude to tell him otherwise.

Until people start including their complete resume, portfolio and SOL test scores with each "problem" it makes sense to ask the simple questions first. Most problems I have seen solved in this forum had very simple solutions and we all like to bounce issues off each other without insults....or you will not have many replies next time. Just my opinion.

06-19-2009, 01:52 PM   #9
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guys

while I appreciate the moral support, there is no reason to jump all over another forum member,

Lets move on to getting the lens fixed
06-19-2009, 02:21 PM   #10
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And I meant no offense. I guess I should have put "LOL" when I said that, but I was interrupted by friends who had driven over 4,000 miles to come see me. I just didn't mean for it to sound like you two thought it meant.

Now back to the problem and the answers.. Lowell, I do appreciate your help.

And Dave thanks too. Especially for the photo.

I'll take a quick snap shot of this lens so you can see the inside.

I thought I would, but my little Nikon point and hope doesn't want to focus and then it flares because of the metal. Dave how do I get the aperture ring off?

Last edited by photolady95; 06-19-2009 at 02:35 PM.
06-19-2009, 07:19 PM   #11
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Never mind. I know. Had a brain freeze when I asked that question. Soon as I get that off, I'll try again to post a photo.
06-20-2009, 11:26 AM   #12
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Cannot get photos of the inside of this lens, so will just trash the thing. Also, can't see what is wrong.
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