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09-14-2019, 10:16 PM   #1
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K-S2 with 50-200 odd failure to focus

I had my K-S2 with the cheapy 50-200 set to full auto, except focus was changed to back button. The picture was just an open box of chocolates on a table and there was a lamp directly above it. The box filled up most of the frame, it didn't matter what zoom I was at or how far away, same behaviour. The little focus indicator turned on and no beep signifying it was in focus even though the image appeared to be in focus. As a result it refused to take the image.

Seems very odd, I pointed all around the table, floor, room, etc and it had no problems locking on and shooting. I eventually resorted to just manual focus to get the shot.

After, I pulled out my Q-S1 + 06 and it had no problems getting focus.

What could the problem be? I've never had it fail even in fairly low light or low contrast situations. I have even snapped a tiny speck of an eagle way up against a cloudless blue sky. This seemed like an absolutely normal shot, not too dark or bright. Indoors, target with decent amount of detail and texture. I suppose I should pull the shot out so you can see but I don't have the camera with me right at the moment...

09-15-2019, 06:09 AM   #2
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I'd suggest low light and a slow lens put the camera at the edge of focusing limits. The QS1 + 06 has a much faster aperture which likely helped it's focusing system. If you have a faster lens handy for the ks2 I'd try to get a comparison of the 50-200 and the faster lens to see if the difference is enough to make it work.

Also the focus mirror can get dust/debris on it which can make focusing harder to achieve. Try liveview in any follow up test as it bypasses that mirror and uses contrast vs phase as it's focusing method.
09-15-2019, 01:22 PM   #3
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Was the box reflective or did it offer no good target for the af to catch onto, like very contrasty lines?
09-15-2019, 07:34 PM   #4
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QuoteOriginally posted by EFats Quote
I had my K-S2 with the cheapy 50-200 set to full auto, except focus was changed to back button. The picture was just an open box of chocolates on a table and there was a lamp directly above it. The box filled up most of the frame, it didn't matter what zoom I was at or how far away, same behaviour. The little focus indicator turned on and no beep signifying it was in focus even though the image appeared to be in focus. As a result it refused to take the image.

Seems very odd, I pointed all around the table, floor, room, etc and it had no problems locking on and shooting. I eventually resorted to just manual focus to get the shot.

After, I pulled out my Q-S1 + 06 and it had no problems getting focus.

What could the problem be? I've never had it fail even in fairly low light or low contrast situations. I have even snapped a tiny speck of an eagle way up against a cloudless blue sky. This seemed like an absolutely normal shot, not too dark or bright. Indoors, target with decent amount of detail and texture. I suppose I should pull the shot out so you can see but I don't have the camera with me right at the moment...
Are you sure you were in focus range? I've had something similar occur...where focus was right at the close limit...viewfinder looks in focus, but camera doesn't signify focus...I lean back a few inches and focus locks.



09-15-2019, 08:10 PM   #5
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It was an open box of chocolates and each one had lots of little bits and things to provide plenty of contrast that should've been easy to lock on to.
I don't think light was a problem, as I said, there was a light right over it and I randomly pointed around the room, on the table, etc and no problem getting focus. I've been in far darker situations and had no problem getting a shot.

At first I thought I was too close for mininum focusing but I stepped up on a chair and went way back and still no luck. At any rate, the table was at the same distance... At one point I'm sure I was close to about 1 m away, which should be plenty, no?

Anyways, just curious. I'll see if I can replicate the problem...
09-15-2019, 10:07 PM   #6
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QuoteOriginally posted by EFats Quote
It was an open box of chocolates and each one had lots of little bits and things to provide plenty of contrast that should've been easy to lock on to.
I don't think light was a problem, as I said, there was a light right over it and I randomly pointed around the room, on the table, etc and no problem getting focus. I've been in far darker situations and had no problem getting a shot.

At first I thought I was too close for mininum focusing but I stepped up on a chair and went way back and still no luck. At any rate, the table was at the same distance... At one point I'm sure I was close to about 1 m away, which should be plenty, no?

Anyways, just curious. I'll see if I can replicate the problem...
Chocolate is dark... And if you can recreate it try a faster lens with no other changes. If possible keep the same focal length.
09-16-2019, 06:11 AM   #7
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QuoteOriginally posted by EFats Quote
At one point I'm sure I was close to about 1 m away, which should be plenty, no?
As the minimum focus distance for the 50-200 is 110cm, no, that would be close, but not enough.

The easiest way to get to maximum magnification ratio is to set focus to manual, turn the focus ring to the close end of the scale and move the camera away from the target, shutter half clicked and focus points on target, until the camera confirms focus.
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