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02-08-2008, 02:51 PM   #1
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Focus issues?

I was taking some indoor, medium-lit pictures with my FA50 of people sitting fairly still, with plenty of light for AF. Here's an example:



Focusing on the face, the results were less than ideal. 100% crop:


I took another shot manual focus, and got this, 100% crop:


Much better!

A few minutes ago I decided to print up and use the infamous focus test, here are some results from my Sigma 28mm f1.8 (100% crop):


and FA 50 f1.4 (100% crop):


The 28mm did fairly well on the chart. Some of the test pics had as much as 10mm front focus, but about half of them were spot on. The 50mm, however, is a bit hard to test. We're all aware that it isn't a particularly sharp lens at f1.4, but this is pretty bad. I can't even tell if it's in focus . Any suggestions from other people with the FA50? I'm contemplating whether or not I should complain to Pentax, but I'm not really sure how normal these results are. This K10d is my first experience really using autofocus, so I'm not quite sure if autofocus is actually expected to be spot on, every time.

Comments or suggestions would be appreciated!

02-08-2008, 03:39 PM   #2
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QuoteOriginally posted by benplaut Quote
I was taking some indoor, medium-lit pictures with my FA50 of people sitting fairly still, with plenty of light for AF. (snip)

Yes, but were you actually focusing on the exact spot you've cropped out in images above? Remember the K10D has multiple focus points, meaning it may be focusing on something else (the guitar or his left hand in the first image, for example). The last image (all blurred) looks more like camera shake than a focusing issue. Beyond that, I suggest searching for the many other threads in this forum about this subject since I doubt anything new can be added at this point.

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02-08-2008, 06:58 PM   #3
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Thanks for the input, I'm going to keep on using the equipment until there are more or less issues!

In response to those Q's (if anyone else has suggestions), I always use center point focus (focus then recompose), and the tests were done on a tripod--all of the FA50 images looked similar.

Shooting again indoors tonight (in flourescent!), I'll see what happens.
02-08-2008, 11:48 PM   #4
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FA 50/1.4 is an old lens, maybe AF does not work that well with DSLR's? I sold mine because AF was not reliable with K100D. It's not very sharp wide open but should be usable.

02-09-2008, 01:36 AM   #5
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You have to get used to how this lens focuses, at least that's what I've learned. Also: focus recomposing throws off your focus by an inch or two
Why Focus-Recompose Sucks
Keep that in mind ;D
02-09-2008, 04:26 AM   #6
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QuoteOriginally posted by hudsong Quote
You have to get used to how this lens focuses, at least that's what I've learned. Also: focus recomposing throws off your focus by an inch or two
Why Focus-Recompose Sucks
Keep that in mind ;D
Yep, I'm aware of that. But it doesn't explain front focus
I shot more tonight and it "seems" ok on the camera screen. When I upload and go through them tomorrow, we'll see.
02-10-2008, 01:37 PM   #7
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I've noticed front focus issues with this lens too. It seems to simply pick the most contrasty object in the viewfinder and focus there, no matter where you put that AF point... I took a few shots of my sister behind a big sound board, with the AF sensor directly on her, and every single time it focused on the sound board, a good foot in front of her. It was infuriating. In other cases, it focuses on the very extreme edge of a pair of eyeglasses perfectly... Weird.
02-10-2008, 02:05 PM   #8
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Is the focus point where you think it is?

QuoteOriginally posted by hudsong Quote
I've noticed front focus issues with this lens too. It seems to simply pick the most contrasty object in the viewfinder and focus there, no matter where you put that AF point... I took a few shots of my sister behind a big sound board, with the AF sensor directly on her, and every single time it focused on the sound board, a good foot in front of her. It was infuriating. In other cases, it focuses on the very extreme edge of a pair of eyeglasses perfectly... Weird.
Perhaps the focus point is not where it is marked in the viewfinder. This can be tested for your camera. Set up something such as newspaper - I use my bookcase - and a tripod. Set the camera on the tripod, and aim it very carefully from various distances. You may find the focus point to be a bit below or above where it appears to be in the viewfinder.

02-11-2008, 08:51 AM   #9
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I found the best way to be reliable with focussing in darker situations is to manually focus on what I want ... and not use AF at all. Only in a few cases .. but if i find that AF isn't working as well as I like ... I switch to MF.
02-11-2008, 09:55 AM   #10
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FWIW my K10D's, (I had two of them) would FF and BF on a regular basis, where the subject was just a bit out of focus and this is using MF in the viewfinder.



I finally sold the last one and am now using my DS which is always spot on with focus, both MF and AF.

Tom
02-11-2008, 10:16 AM   #11
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QuoteOriginally posted by ennacac Quote
FWIW my K10D's, (I had two of them) would FF and BF on a regular basis, where the subject was just a bit out of focus and this is using MF in the viewfinder.

I finally sold the last one and am now using my DS which is always spot on with focus, both MF and AF.

Tom
When focusing manually, how can it FF or BF? You are the one telling it where to focus.
02-11-2008, 12:05 PM   #12
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It is a K10D focus issue, even though it is in focus in the viewfinder, that is not where it focuses which is what BF and FF means.

It does not mean you focused in front of the subject of behind the subject.
02-11-2008, 01:27 PM   #13
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QuoteOriginally posted by ennacac Quote
It is a K10D focus issue, even though it is in focus in the viewfinder, that is not where it focuses which is what BF and FF means.

It does not mean you focused in front of the subject of behind the subject.
I know what they mean. And again, when focusing manually, it's you that determines what is in focus, not the camera. If the shot still isn't in focus, there are a bunch of reasons why, but none of them are the camera.
02-11-2008, 03:35 PM   #14
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So you are saying when I focus the image in the viewfinder using MF and when the resulting image is out of focus it is not the cameras fault it is mine, how bizzare!

Lucky for me I don't have the same issue with my DS which matches the viewfinder focus and the final image perfectly.

Tom
02-13-2008, 06:48 PM   #15
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OK, back on topic
I repeated the test today under much better lighting and with a more solid tripod. Overexpose +2EV, and it's easy to see where the focus is and should be!

The 28mm frontfocused by between 6mm-10mm on that chart, and the 50mm by about 6mm--that's a close enough margin for me to consider it a body problem and not a problem with two lenses. I went into the service menu and, after a bunch of testing, settled on -40 being the right choice. Focus is now spot-on for both lenses! Any problems from here on out are my fault, not the camera
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