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08-13-2007, 03:58 PM   #16
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focus problems...

This is interesting:

A picture take from the computer screen
Again Pentax K10D, Sigma 18-200
Common settings: 200mm, 1600 ISO.
Camera stabilized on a tower of CD boxes :-)
Attached picture is a 100% crop; the "GHz" was more or less in the center of the original picture.

First with F/5.6, 1/90sec
Name:  f6.jpg
Views: 410
Size:  26.6 KB

Then with F/38, 1/2 sec
Name:  f38.jpg
Views: 406
Size:  29.0 KB

I guess my problems are now reduced to either:
a) the lens (bad resolution at large apertures)
or
b) focussing problems (the F/38 increases the DOF, which masks the focus error ? )

I still don't understand why the blur is more pronounced on the vertical lines...

Erik.


Forgot to mention: SR was off in both cases.

08-13-2007, 04:24 PM   #17
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interesting I have had my K10D a couple of weeks now and have played with all the settings in a studio environment and guess what when i use my sigma dg 28-300 lens this also is out of focus at about 200, and yes i am using a tripod and remote release. I have also noticed that when i use manual focus and go back to auto the lens hunts for ages before focusing. Also found unsharp images when using my sigma apo 400 lens. have used same lens on dl without problems????
I spent a whole day in the studio with both cameras on tripods taking photos on same settings of same subject with same lens. exposure also not as good on K10D compaired to DL
08-14-2007, 07:59 AM   #18
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QuoteOriginally posted by lipsestraat Quote
This is interesting:

A picture take from the computer screen
Again Pentax K10D, Sigma 18-200
Common settings: 200mm, 1600 ISO.
Camera stabilized on a tower of CD boxes :-)
Attached picture is a 100% crop; the "GHz" was more or less in the center of the original picture.

First with F/5.6, 1/90sec
Attachment 4304

Then with F/38, 1/2 sec
Attachment 4305

I guess my problems are now reduced to either:
a) the lens (bad resolution at large apertures)
or
b) focussing problems (the F/38 increases the DOF, which masks the focus error ? )

I still don't understand why the blur is more pronounced on the vertical lines...

Erik.


Forgot to mention: SR was off in both cases.
If you ignore the beep can you just MF till it's sharp in the viewfinder and then take a sharp picture? I'm a bit surprised that the camera would "lock" w/ that much blur...
08-14-2007, 01:26 PM   #19
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QuoteOriginally posted by jeffkrol Quote
If you ignore the beep can you just MF till it's sharp in the viewfinder and then take a sharp picture? I'm a bit surprised that the camera would "lock" w/ that much blur...
YES ! This fixed it.
And even more: when I switch back to AF.s the blur reappears.

I used F/6.7 to verify this and the DOF isn't that big, so I had to adjust only a very tiny amount to get the better focus. In the viewfinder the difference is very small.

Unfortunately I have a 1.3 firmware, so I can't start experimenting with focussing parameters (I thought this was possible with 1.1 firmware using some debug settings).

Is this now the end of the road for me ?

Thanks,
Erik.

08-14-2007, 03:05 PM   #20
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last update.

Some more experimenting showed that it was the polarizer which caused the focussing problems !

I removed the polarizer and now get sharp pictures, even handheld (with SR on).

Thanks you all for the helpful hints !
Erik.
08-14-2007, 04:55 PM   #21
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QuoteOriginally posted by lipsestraat Quote
Some more experimenting showed that it was the polarizer which caused the focussing problems !

I removed the polarizer and now get sharp pictures, even handheld (with SR on).

Thanks you all for the helpful hints !
Erik.
COOL, glad it turned out to be a simple fix.....
out of curiosity, do you know if the polarizer was circular or linear? Most digitals require a circular polarizer to not screw up the AF. Most people have reported that linears are fine for pentax cameras but I always wondered if there wasn't a "gotcha" somewhere.
08-14-2007, 05:11 PM   #22
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Mentioning the polarizer at the beginning of the thread may have helped us figure this out much sooner. But be that as it may, I'm glad and relieved to learn that you don't have a bum lens.

I don't have much experience with auto-focus lenses, owning only two and planning to sell them both in the near future, but it seems to me that while they may have manual focus rings on them they aren't really designed for fine adjustments, typically having a much shorter throw. At the very least they're out there at a somewhat awkward position, on the end of the lens.
08-16-2007, 08:25 AM   #23
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First question - What is that you are shooting? Some weird fenced in area?

Use a tripod, turn OFF SR, use a smaller aperature setting and slower shutter speed, and lastly, use the 2 second shutter release delay, it flips the mirror into the lock-up position 2 seconds before actually opening the shutter thus eliminating any possible vibrations and providing you with the sharpest possible photo.

Post up the same photo with those suggestions.

I too had a problem with a Circular Polarizer.. It was an Optika brand, (looks to be a sub-brand of Hoya).. I was having focusing issues like you mentioned, even worse as it would happen at 50mm as well.. Went to the camera shop, swapped in a new Hoya Pro and the problem was gone instantly. So, yes, the CPL can cause issues like that.

Also, in your test photos you state your using ISO 1600.. Why? Such high ISO settings will introduce noise thus unsharpening the image. Try the same photo at ISO 200 or ISO 400 with a shutter of 125 or something. Or, what's wrong with ISO 100? You'll get a much better image by doing so.


Last edited by Tom M; 08-16-2007 at 08:48 AM.
08-16-2007, 02:00 PM   #24
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QuoteOriginally posted by Tom M Quote
First question - What is that you are shooting? Some weird fenced in area?
See my first post.
QuoteOriginally posted by Tom M Quote
Use a tripod, turn OFF SR, use a smaller aperature setting and slower shutter speed, and lastly, use the 2 second shutter release delay, it flips the mirror into the lock-up position 2 seconds before actually opening the shutter thus eliminating any possible vibrations and providing you with the sharpest possible photo.
Aha. This I've never tried yet. Thanks for the suggestion.

QuoteOriginally posted by Tom M Quote
Post up the same photo with those suggestions.
It's a bit difficult to shoot that fence again, since it's prob about 10000km from where I am now, but I tried shooting my computer screen again, and it's difficult to see differences due to SR off or the 2 second delay. Perhaps with other lenses the difference will be bigger.
QuoteOriginally posted by Tom M Quote
Also, in your test photos you state your using ISO 1600.. Why? Such high ISO settings will introduce noise thus unsharpening the image. Try the same photo at ISO 200 or ISO 400 with a shutter of 125 or something. Or, what's wrong with ISO 100? You'll get a much better image by doing so.
Well, I knew about that, but I wasn't interested in the noise from the high ISO. You're right that it improves the picture, but it wasn't the primary problem of the blurry picture.

The polarizer I used was a cheap Targus 62mm C-PL.

Thanks,
Erik.
08-16-2007, 09:48 PM   #25
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I have faced similar problems with my K10D and my Sigma 70-300 and 18-55 kit lens. I just can't rely on AF so if I want to be sure I get a sharp shot, I turn the cam to manual focus and off I go.

I don't even have a clear glass filter on my lenses, so I wish I could say that would solve my issue. Not a big one for me since I have no problems shooting manual, but it's an annoyance none-the-less.
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