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01-17-2014, 08:11 PM   #1
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Pentax-A 35-105 f3.5 Question

I have a Pentax-A 35-105 f3.5 (well actually 2) but one that has some issues with the photos it takes. Appearance-wise there doesn't seem to be any issues (compared to my other copy that is sharp). However, the images are soft and when wide open, blacks are mostly green (center of test chart), and it doesn't begin to compare to my good copy until f8. Anyone have any ideas what may be the culprit? Glass is clear (no fungus, oil, haze), everything looks good. Result are awful at 3.5 and gradually improve to f8 where they are comparable to my good copy of the lens. The only thing I can think of is separation but upon visual inspection that doesn't seem to be the case, unless it can be difficult to observe. Any ideas are appreciated. Thanks.


Last edited by transam879; 11-29-2014 at 09:32 PM.
01-17-2014, 09:18 PM - 1 Like   #2
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Can you observe any evidence of the lens being previously opened for service? (e.g. tool marks on screw heads, retaining rings, etc.)

If so, it's possible that one or more of the element has been reversed when re-assembled.

If there's no evidence of tampering, then it could be lens separation of one of the internal group. Some separation is hard to detect unless you look at it directly and you may not notice it if you just look through the lens.

Also, check to see if any part of the lens is loose or has some wobbliness. If you grab hold of the front most part of the lens, does it wobble or move slightly front and back? Old lenses like this, especially zoom lenses, will tend to have some loosened screws and will need to have them re-tightened.
01-18-2014, 12:42 PM   #3
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Thanks for the input. There was some wobble and I gently tightened all exterior screws (the ones on the barrel started to hairline crack the barrel next to the screw so I backed off those) and most of the wobble went away. Test result was the same, no change. However, I was testing with the zoom maxed out to 105mm. I backed off slightly (just to the right of 105mm) so maybe around 100mm and picture was good wide open. Tested other focal lengths and everything was good. Guessing maybe the zoom was throwing it slightly past 105mm,which the optics weren't designed to operate at? Either way, lens appears to be back in business. Thank you for the input.
01-31-2014, 05:20 AM   #4
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I'd just got one of these. A strange lens. It can be quite sharp when focused well (say in liveview) but my copy has a tendency to lose focus when zoomed. Focus at 105mm on a distant object - perfect. Zoom out a bit without touching the focus ring and it defocuses. Zoom out all the way and back again to the same position (just a bit short of the 105mm end) also without touching the focus ring and it is back in perfect focus.

It could be years of congealed grease, wear (the lens looks as if it had hardly been used) or just a design 'feature'.

I am not brave enough to take it to bits to find out

01-31-2014, 06:52 AM   #5
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QuoteOriginally posted by kh1234567890 Quote
I'd just got one of these. A strange lens. It can be quite sharp when focused well (say in liveview) but my copy has a tendency to lose focus when zoomed. Focus at 105mm on a distant object - perfect. Zoom out a bit without touching the focus ring and it defocuses. Zoom out all the way and back again to the same position (just a bit short of the 105mm end) also without touching the focus ring and it is back in perfect focus.

It could be years of congealed grease, wear (the lens looks as if it had hardly been used) or just a design 'feature'.

I am not brave enough to take it to bits to find out
Sounds like your lens requires servicing.

This model has an unusual zoom design/construction, almost an over-engineered look. However, this lens does suffer quite often from loosening of screws that hold the nylon bushing that glides along the groove (for zooming action) over period of use. I have purchased close to a dozen of these lenses and MOST required servicing relating to this problem before I sold them.

I certainly don't recommend this lens as your first attempt at lens repair.
01-31-2014, 08:12 AM   #6
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QuoteOriginally posted by tom1803 Quote
Sounds like your lens requires servicing.

This model has an unusual zoom design/construction, almost an over-engineered look. However, this lens does suffer quite often from loosening of screws that hold the nylon bushing that glides along the groove (for zooming action) over period of use. I have purchased close to a dozen of these lenses and MOST required servicing relating to this problem before I sold them.

I certainly don't recommend this lens as your first attempt at lens repair.
Thanks for that. I've had a few lenses to bits (and back again) but I can't see myself getting attached to this one to fix it or get it fixed. It was cheap.

It does not seem as wonderful as it is made out to be - quite soft wide open, plenty of CA in the corners even on APS and far too big and heavy to drag about. It gets better stopped down but then just about anything would. Give me a bag of primes instead anytime
02-02-2014, 02:25 PM   #7
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QuoteOriginally posted by kh1234567890 Quote
I'd just got one of these. A strange lens. It can be quite sharp when focused well (say in liveview) but my copy has a tendency to lose focus when zoomed. Focus at 105mm on a distant object - perfect. Zoom out a bit without touching the focus ring and it defocuses. Zoom out all the way and back again to the same position (just a bit short of the 105mm end) also without touching the focus ring and it is back in perfect focus.
That doesn't sound like a problem, but rather normal for many zoom lenses that to do not stay in focus as you zoom in and out.
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