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08-12-2009, 11:31 AM   #1
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K20 Focus problem...

I'm out of my depth on my new K20. Here's a image from the K100 and one from the K20. Both shot with in Manual Mode, AWB, 200 ISO, IS off, tripod @ f/4 using the same Tamron 28-75 Di @ 50mm both focused in the middle of the frame (the bush). Both shot in RAW, imported at size and USM, otherwise untouched.

Here's the K100 shot for reference...

And here's the same shot from the K20, obviously, something's going very wrong with the K20, it seems to be focused in the lower third of the image. What c an I do short of sending it back?
Thanks for any help,
Brian


08-12-2009, 11:39 AM   #2
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what focus mode are you using? There should be a dial on the back right that sets it: auto, sel (selective), * (center).

Is it possible you are using selective focus and focusing on the bottom?
08-12-2009, 11:49 AM   #3
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Can you post 100% crops? I can hardly tell at the moment
08-12-2009, 12:02 PM   #4
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Also:

- It's not the same shot at all - you're clearly either at a longer focal length or closer with the K20D, plus you've framed the shot lower.

- Even if you selected the center point, the bush is actually mostly *above* the center line, and part of the foreground is probably within range of the center focus point. So you cannot really blame the camera for focusing on the forground instead of the bush if it so chooses. You'd need to have selected a focus point in the middle of the bush, or centered and focused there then recomposed (and accepted the possibility of slight discrepancies as a result) in order to guarantee the camera focused on the bush.

- I agree with the previous poster, at the given size it's tough to tell anything at all. but it does look indeed like you used one of the bottom focus points. What does the EXIF say if you run the image through PhotoME or something similar that tells you which focus point was actually used?

08-12-2009, 01:48 PM   #5
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Response...

QuoteOriginally posted by Marc Sabatella Quote
- It's not the same shot at all - you're clearly either at a longer focal length or closer with the K20D, plus you've framed the shot lower.
- Even if you selected the center point, the bush is actually mostly *above* the center line, and part of the foreground is probably within range of the center focus point. So you cannot really blame the camera for focusing on the forground instead of the bush if it so chooses. You'd need to have selected a focus point in the middle of the bush, or centered and focused there then recomposed (and accepted the possibility of slight discrepancies as a result) in order to guarantee the camera focused on the bush.

- I agree with the previous poster, at the given size it's tough to tell anything at all. but it does look indeed like you used one of the bottom focus points. What does the EXIF say if you run the image through PhotoME or something similar that tells you which focus point was actually used?
Sorry, but it's the exact same shot at 75mm from a stationary tripod; the only difference is the K20 / K100 body ... the position, the lens, the settings, the focus point (the bush is vertical center and the focus was the middle of the bush) are all the same. However, assuming pilot error, I'll reshoot and see what I come up with; if anything changes, I'll repost, if not, then there's something out of whack on the K20.

Brian
08-12-2009, 02:31 PM   #6
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Have you done a focus test and adjustment (Page 106 of the manual).?

I wasnt happy with my K20 on occasion and went through this process with each lens (some of them were way out, others were spot on).....I'm a lot happier now.

Another quick & dirty test is line up three items (I use AA batteries), focus on the middle one and see what happens.

Takes a bit of time, but worth the effort.
Cheers
Grant
08-12-2009, 02:44 PM   #7
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QuoteOriginally posted by FHPhotographer Quote
[B]Sorry, but it's the exact same shot at 75mm from a stationary tripod; the only difference is the K20 / K100 body ... the position, the lens, the settings, the focus point (the bush is vertical center and the focus was the middle of the bush) are all the same.
Then perhaps oyu did something different in PP? I mean, isn't it *obvious* to you just by looking at the images that they are different? That the bush is bigger and higher in the second shot? And not by a little - by a pretty significant amount?

Anyhow, that's neither here nor there. The real question is how well you controlled where the camera focused. If you used center point on #2, then the answer is, you *didn't* control where the focus happened - you allowed the camera to focus on the foreground.
08-12-2009, 03:52 PM   #8
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Ah hah, it's the lens not the camera...

QuoteOriginally posted by Marc Sabatella Quote
Then perhaps oyu did something different in PP? I mean, isn't it *obvious* to you just by looking at the images that they are different? That the bush is bigger and higher in the second shot? And not by a little - by a pretty significant amount?

Anyhow, that's neither here nor there. The real question is how well you controlled where the camera focused. If you used center point on #2, then the answer is, you *didn't* control where the focus happened - you allowed the camera to focus on the foreground.
Just reshot and it's the lens, not the K20: very sharp @ 28 and 35mm, softer @50mm and very soft @ 75mm. If the AF Adjustment feature (p106 of the manual) changes the 50-75mm range, will that put the 28-35mm range out of whack?
And another thought, can the camera see the 28-75 as two lenses and adjust them as two separate lenses (28-35 and 50-75) to set the focus for each?

Brian


Last edited by FHPhotographer; 08-12-2009 at 03:57 PM.
08-12-2009, 04:20 PM   #9
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To my knowledge, the k20d can store 20 different LENS; I think you may be mistaken this for focal range?
08-12-2009, 05:22 PM   #10
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Waiting to hear...

QuoteOriginally posted by systemA Quote
To my knowledge, the k20d can store 20 different LENS; I think you may be mistaken this for focal range?
Don't know, but I see posts from folks who've tried the AF Adjust with the Tamron and ended up screwing up on the AF on the wide angle end. I've got a query in to both Pentax and Tamron, and although I don't expect much help from them, I'm going to wait to hear before trying any adjustment.
Brian
08-12-2009, 07:21 PM   #11
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QuoteOriginally posted by FHPhotographer Quote
Don't know, but I see posts from folks who've tried the AF Adjust with the Tamron and ended up screwing up on the AF on the wide angle end. I've got a query in to both Pentax and Tamron, and although I don't expect much help from them, I'm going to wait to hear before trying any adjustment.
Brian
Its easy to turn it (AF Adjust) off though Brian.
I would try it and see, every lens combination is going to be different....if you dont like the result just set the values back to zero. Doesnt take long.

Cheers.
08-12-2009, 09:22 PM   #12
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A focus test...

QuoteOriginally posted by Mallee Boy Quote
Its easy to turn it (AF Adjust) off though Brian.
I would try it and see, every lens combination is going to be different....if you dont like the result just set the values back to zero. Doesnt take long.

Cheers.
Well, I took your advice set the AF Adjustment (several settings but -10 looked the best), and reset it to the default of +/-0, and took shots of a focus test page for both. This is the result
First, the AF Adjustment @ -10:

The the default @ 0:

I see an improvement, but it's still coming out soft @75mm contrasted with 28mm, and it gets softer at longer distance,
Brian

Last edited by FHPhotographer; 08-12-2009 at 09:41 PM.
08-13-2009, 03:01 AM   #13
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Brian it appears you have a fair bit of front focus...try it on -2 or -3. As the man said..costs nothing to play!!!
08-13-2009, 08:47 AM   #14
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Pentax doesn't care about it...

QuoteOriginally posted by Daveinozbikes Quote
Brian it appears you have a fair bit of front focus...try it on -2 or -3. As the man said..costs nothing to play!!!
I tried using the K20s AF Adjustment feature using every setting from - 10 through +5 and while I can get a slight improvements of various amounts on closer shots, anything from about 8-10'+ in the 50-75mm range that the camera says is in focus shows up very soft on screen or printed.

Customer service, apparently doesn't much care what happens if you're not using a Pentax lens on one of their cameras. Their rather dismissive response about what they'd suggest was, "We don't test our cameras with other manufacturers' lenses ... I suggest you contact Tamron to find out if their lens can be made to work on the K20D."

I've done that and will see what Tamron says, but I hope this isn't typical of Pentax customer service. And if it's typical of the industry, then it's probably our fault as consumers for buying into this kind of noblesse oblige.

And please don't flame me with the customary "if you don't like it, leave, who cares" responses.

Brian
08-13-2009, 09:38 AM   #15
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It's the lens...I went through 3 copies of it on my K10D before giving up. It'd either BF or FF at the wide or tele end and I didn't have focus adjustment. Try calibrating it for 50mm and live with it or get another lens and see if you get lucky in Tamron roulette ;-)

You can dig up my old thread on this in the lens forum...
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