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02-15-2015, 11:38 AM   #16
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QuoteOriginally posted by ak_kiwi Quote
One of the things I too found with my K3, when compared to the K-5 series cameras, was it really showed up small errors in focusing. After many hours shooting my trusty old focus target (and cat dogs and kids etc) I came to the conclusion that the targets I was using were just not good enough to give repeatable accurate results. I found it was imperative to have a focus target parallel to the sensor plane - and the ability to confirm this parallel was critical to developing accurate evaluations of tests. In the end I purchased a LensAlign focus target which in about 5 minutes told me what I needed to know to fix the problem.

However,just before you buy a LensAlign - try one of these targets on a repeatably well lit wall. Square off the camera to the wall and make sure it is on center with the target also. Test your close auto focus Vs further away auto focus by comparing with shots using live view (with focus peaking) and manual focus.
If you want to get real keen arrange 4 more targets to mark out the corners of the frame. This will give you a check on possible decentering and replaces the "newspaper check" method.
Thanks alot for your valuable info. Well, K-3 indeed looks like it has a steep learning curve, but I believe it will pay off all the efforts in the future-Frankly many shots so far are not as good as the ones that I got from my Canon T2i and Tamron 17-50 combo, which discourages me sometimes. I'll try that and see how it goes!

02-16-2015, 04:45 AM   #17
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Looking at the tree image, I'd be inclined to think the softness of the far left tree is primarily the tree being too close to the lens versus your infinity focus point being on the mountains and therefore simply being out of focus. Plus perhaps a little bit of edge weakness although I don't believe that played a large part here. I'm not aware of this lens having field curvature issues which could be another potential cause of soft edges. Diffraction should cause softness more generally across the image and not be confined just to the extreme edges so I tend to discount that in this sample image.

I have a small depth of field calculator app on my phone which tells me if that tree is closer than 20-25 feet from the camera, it will be rendered out of focus even at F11. So I suspect the tree doesn't tells you anything about focus accuracy. If the far distance is sharp, at F11 small focus errors are also probably hidden by the depth of field. Again you may not be learning much.

Looking at the dog shots (cute mutt by the way), it seems to suggest the focus correction is biased too forward.

Roughly depth of field should be 1/3rd in front of the point of focus and 2/3rds behind. Maybe you have pulled the focus just a bit too far forward using the test chart putting the dog just out of focus at f2.4. Maybe back off to +3 and try the portrait distance again with pooch or another subject.

Another way to check autofocus is to use live view moving the live view focus square with the control buttons to be exactly on the target. Let live view then focus on the target. Put a small piece of masking tape on the lens over the distance scale. Mark where the focus mark of the lens is onto the tape. Go out of live view and use the normal phase focus to focus on the same subject marking sure the selected focus point is over the subject. I always use the centre focus point for calibration. Check if the marks still align. Repeat several times letting the lens refocus from both infinity and minimum focus settings. Note if the mark settles in a generally consistent place. If so, then any gap between the pen mark and the engraved focus mark gives you an indication of which way to change the focus adjustment. Make a small change and test again until the best outcome is determined.

You are looking for small changes so use a tripod to ensure consistent distance. Also perform in natural light. Tungsten light upset K-5 autofocus, K-3 appears free of this, but given we are chasing down small errors, taking this possible cause of inconsistent results out of the equation does no harm.
02-16-2015, 06:10 AM   #18
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Miserable camera (K-3, should go to service?) or miserable lens (DA* 16-50mm/2.8, Q. as above?) - focusing was on a birch in a center of the picture.
The rig: K-3, DA* 16-50mm/2.8, RRS L-Bracket, Arca Swiss ballhead with QR, Gitzo Explorer cf legs, Hama wired remote, 2 sec self-timer or mirror-up.
Before each of the shots the lens focussing barrel was turned i) to the close-up, ii) to the infinity, than half-press shutter, than release (cable remote) after visible & audible K-3 body confirmation.

Last edited by Prakticant; 04-15-2015 at 12:36 AM.
02-16-2015, 10:36 AM   #19
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Same DA* 16-50mm/2.8 lens, brand new K-3 body.

As I had a chance to try my (faulty?) DA* 16-50mm/2.8 lens with brand new out of the box K-3 body, I've made couple of shots of the same birch tree.
Same lens, different body, different shots.
These pictures are without tripod support, on default K-10 settings (I just changed contrast AF from face to spot).
What I can see, the K-3 body which I own seems to be faulty (bad not repeateable phase detection focussing, back focussing).

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02-16-2015, 11:10 AM   #20
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QuoteOriginally posted by Prakticant Quote
Miserable camera (K-3, should go to service?) or miserable lens
I would suggest you do a methodical focus test with a proper focus target (see my post #15 in this thread).
It would be beneficial to re-post in a new thread with your results so answers can be directed to your particular circumstance.
02-16-2015, 11:14 AM   #21
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QuoteOriginally posted by southlander Quote
Looking at the tree image, I'd be inclined to think the softness of the far left tree is primarily the tree being too close to the lens versus your infinity focus point being on the mountains and therefore simply being out of focus. Plus perhaps a little bit of edge weakness although I don't believe that played a large part here. I'm not aware of this lens having field curvature issues which could be another potential cause of soft edges. Diffraction should cause softness more generally across the image and not be confined just to the extreme edges so I tend to discount that in this sample image.

I have a small depth of field calculator app on my phone which tells me if that tree is closer than 20-25 feet from the camera, it will be rendered out of focus even at F11. So I suspect the tree doesn't tells you anything about focus accuracy. If the far distance is sharp, at F11 small focus errors are also probably hidden by the depth of field. Again you may not be learning much.

Looking at the dog shots (cute mutt by the way), it seems to suggest the focus correction is biased too forward.

Roughly depth of field should be 1/3rd in front of the point of focus and 2/3rds behind. Maybe you have pulled the focus just a bit too far forward using the test chart putting the dog just out of focus at f2.4. Maybe back off to +3 and try the portrait distance again with pooch or another subject.

Another way to check autofocus is to use live view moving the live view focus square with the control buttons to be exactly on the target. Let live view then focus on the target. Put a small piece of masking tape on the lens over the distance scale. Mark where the focus mark of the lens is onto the tape. Go out of live view and use the normal phase focus to focus on the same subject marking sure the selected focus point is over the subject. I always use the centre focus point for calibration. Check if the marks still align. Repeat several times letting the lens refocus from both infinity and minimum focus settings. Note if the mark settles in a generally consistent place. If so, then any gap between the pen mark and the engraved focus mark gives you an indication of which way to change the focus adjustment. Make a small change and test again until the best outcome is determined.

You are looking for small changes so use a tripod to ensure consistent distance. Also perform in natural light. Tungsten light upset K-5 autofocus, K-3 appears free of this, but given we are chasing down small errors, taking this possible cause of inconsistent results out of the equation does no harm.
I think that makes a total sense. Just wanted to know either my camera or lens is not defective in any way because my return/exchange period with Adorama is ending in about 10 days. I'll adjust AF to +3 and see how it goes. Thanks for the great information!
02-16-2015, 11:18 AM   #22
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QuoteOriginally posted by ychousa Quote
Does that mean any aperture beyond 9 would cause diffraction? I'm a bit confused.
f/9 is where it starts to set in. You may not see it in every shot. But f/9 is where the sharpness will start to decline due to diffraction. It will be quite mild at f/9 and may be rather obvious by f/13.
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