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09-07-2009, 06:46 PM   #1
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FA50 lost infinity focus?

I picked up my FA50 for the first time in a few months today (was going to a mining museum, where I figured it might be dark inside). Unfortunately, to my dismay, when I arrived I noticed that my camera (K200D) wouldn't focus on distant objects. I mean that the green polygon focus indicator would flash.

Initially I figured it was possibly some sort of low light focus problem, but then I noticed that I could focus easily on nearby objects, and besides I was outside and it was overcast, but still the middle of the day and there was plenty of light.... especially for the FA50.

I took some shots, but after messing around with AF and manual focus basically concluded that the lens no longer focusses at infinity. It used to be that when focussed on distant object the lens was right up against the stop, but now even at the stop the focus point is closer and distant objects are OOF.

I posted an example here:

http://turing.phas.ubc.ca/fa50oof.jpg

(full size 100 quality: http://turing.phas.ubc.ca/fa50oof-full.jpg)

I was focussed at infinity. The cliffs in the background across the water are blurry yet the railing in front of me is fairly sharp (f/4 1/350s). I don't think I'm making any simple mistakes with the photography here. I took a bunch of shots and they all have this problem.

The lens used to focus fine at infinity, both by the focus confirmation green indicator and the resulting photographs. Any ideas how this could have happened? I'm basically positive the lens hasn't had any mechanical damage, it's just been sitting on my desk, but I don't see how this could be an electrical problem, since I have the same issue with manual focus...

Other lenses continue to work fine. I'm grateful for any ideas, hopefully I am just missing something totally trivial...


Last edited by sewebster; 09-08-2009 at 09:09 AM.
09-07-2009, 09:20 PM   #2
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It looks like the target you are focusing on is very low contrast and the focusing algorithm may be having problems. Have you tried just manually setting the focus to infinity and taking a picture of a distant object. Also, there is so much atmosperic haze and low contrast due to the distance involved that it is difficult to judge focus. It definitely looks like it focused on the rail, though.

Did you have the camera set to center spot focus? Try focusing on a high contrast target in the middle of the frame at a closer distance (say 100 feet).
09-07-2009, 09:24 PM   #3
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QuoteOriginally posted by pentaxman Quote
It looks like the target you are focusing on is very low contrast and the focusing algorithm may be having problems. Have you tried just manually setting the focus to infinity and taking a picture of a distant object. Also, there is so much atmosperic haze and low contrast due to the distance involved that it is difficult to judge focus. It definitely looks like it focused on the rail, though.

Did you have the camera set to center spot focus? Try focusing on a high contrast target in the middle of the frame at a closer distance (say 100 feet).
Yeah, I tried manual focus, in fact I think that picture I posted IS manually focussed at infinity. Whenever I used AF I used centre spot focus, I'm definitely not focussed on the railing I am also sure that I did not focus "past infinity" as is possible on some lenses, which should also be clear from the railing being in focus. I have some other pictures I took of this huge mining dumptruck which was quite high contrast and not nearly so far away. Also out of focus.

Seems a very odd problem to start happening without dropping the lens or something. I guess the stop could have slipped somehow.
09-07-2009, 09:40 PM   #4
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I have had manual focus lenses become unable to focus at infinity, but it is usually close. In this instance it is fairly easy to adjust by a minor disassembly of the lens.

In you case, it sounds like your focus problem is WAY off. I would guess that you have had some mechanical failure of your focusing mechanism. It is weird that it would just suddenly start doing this, though. I would suggest sending it to Pentax and letting them check it out.



QuoteOriginally posted by sewebster Quote
Yeah, I tried manual focus, in fact I think that picture I posted IS manually focussed at infinity. Whenever I used AF I used centre spot focus, I'm definitely not focussed on the railing I am also sure that I did not focus "past infinity" as is possible on some lenses, which should also be clear from the railing being in focus. I have some other pictures I took of this huge mining dumptruck which was quite high contrast and not nearly so far away. Also out of focus.

Seems a very odd problem to start happening without dropping the lens or something. I guess the stop could have slipped somehow.


09-09-2009, 01:02 AM   #5
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It looks quite strange. I don't even know how it may happen.
May be lens was disassembled and assembled wrongly.
I have few manual lenses that can be assembled so it'll result in with wrong focus ranges.
09-09-2009, 05:15 AM   #6
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My FA50, mounted on a K200D, threw itself out last infinity a couple weeks ago. It looked as if it came off its tracks internallyy, and it extended about 1/16 of an inch further than it was suppsed to, and then it wouldn't pop back in. I had to send it in for service...forunately for me, it happened 11 months into a 12 month warranty.
09-09-2009, 09:22 AM   #7
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The only other thing I can think of would be if the sensor in the camera shifted slightly (moved further back into the camera) and now the FA50 can't move the element close enough to focus. Other lenses might not be affected because they have more travel "beyond infinity" (eg. 16-45 and kit). But I'm not sure this is really possible, either physically, or without affecting focus on other lenses (while being so obvious on the 50).

Edit: the 50 isn't totally broken though, pictures taken of closer subjects seem fine.

Last edited by sewebster; 09-09-2009 at 10:23 AM.
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