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06-10-2008, 03:43 AM   #1
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K20D AF woes

I have owned my K20D for a little over a month now.

Originally I bought a Tamron 28-300mm LD IF Super Zoom lens. It failed to correctly focus at long focal lengths and didn't produce the clarity I was looking for. I sold that recently and purchased a Tamron DiII 18-200mm zoom.

Again, the K20D has trouble auto-focusing correctly and regularly gives me shots where the focus is nothing to be proud of.

Now I know for a fact the lenses are well proven and have good reviews. I can now only deduce the K20D body is possibly faulty, or that I am expecting too much clarity from a 15MP camera and that I have to be SUPER careful that I am holding the camera perfectly still even at very fast shutter speeds.

My K100D would produce fantastic crisp shots even with the worst of camera shake and no SR active at 1/400 and over on moving targets.

The K20D gives quite blurred shots even with SR turned on and shutter speeds in excess of 1/750.

What should I do? Lose my camera for possibly weeks or months and have it sent back for testing or is this just par for the course with this body?

06-10-2008, 04:30 AM   #2
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QuoteOriginally posted by NicholasN Quote
I have owned my K20D for a little over a month now.

Originally I bought a Tamron 28-300mm LD IF Super Zoom lens. It failed to correctly focus at long focal lengths and didn't produce the clarity I was looking for. I sold that recently and purchased a Tamron DiII 18-200mm zoom.

Again, the K20D has trouble auto-focusing correctly and regularly gives me shots where the focus is nothing to be proud of.

Now I know for a fact the lenses are well proven and have good reviews. I can now only deduce the K20D body is possibly faulty, or that I am expecting too much clarity from a 15MP camera and that I have to be SUPER careful that I am holding the camera perfectly still even at very fast shutter speeds.

My K100D would produce fantastic crisp shots even with the worst of camera shake and no SR active at 1/400 and over on moving targets.

The K20D gives quite blurred shots even with SR turned on and shutter speeds in excess of 1/750.

What should I do? Lose my camera for possibly weeks or months and have it sent back for testing or is this just par for the course with this body?
Check for Front Focus or Back focus. Once you have determined which it is, go into the menu area of the K20D and make the necessary correction.

If it is not FF/BF, then you need to send your camera in to Pentax and have them repair it.
06-10-2008, 05:31 AM   #3
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Which is the best method for testing FF/BF?
06-10-2008, 05:33 AM   #4
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With regard to the FF/BF correction in the K20D menu, what form of measurement do each of the notches mean? Say I select -2 what exactly does that mean?

06-10-2008, 06:29 AM   #5
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Still think the lens choice is the issue

The ability to detect lens error by the K20D is vastly superior to the K100D. A relatively cheapo (though 'highly regarded' at the time) lens may no longer be up to the job.

Before you condemn the K20D, may I suggest that you test it with a high quality Pentax designed and produced lens?

Your K20D really raises the bar on quality. Just because a last year's lens/camera combination worked reasonably well does not mean it will continue to hold true. I've found that K20D does not tolerate dumbing down very well. You simply may be asking too much.

...my 2 cents...
06-10-2008, 06:34 AM   #6
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Post samples of your problem.
06-10-2008, 11:51 AM   #7
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QuoteOriginally posted by NicholasN Quote
I have owned my K20D for a little over a month now.

Originally I bought a Tamron 28-300mm LD IF Super Zoom lens. It failed to correctly focus at long focal lengths and didn't produce the clarity I was looking for. I sold that recently and purchased a Tamron DiII 18-200mm zoom.

Again, the K20D has trouble auto-focusing correctly and regularly gives me shots where the focus is nothing to be proud of.

Now I know for a fact the lenses are well proven and have good reviews. I can now only deduce the K20D body is possibly faulty, or that I am expecting too much clarity from a 15MP camera and that I have to be SUPER careful that I am holding the camera perfectly still even at very fast shutter speeds.

My K100D would produce fantastic crisp shots even with the worst of camera shake and no SR active at 1/400 and over on moving targets.

The K20D gives quite blurred shots even with SR turned on and shutter speeds in excess of 1/750.

What should I do? Lose my camera for possibly weeks or months and have it sent back for testing or is this just par for the course with this body?
AF inaccuracy is a big enough problem that manufacturers are putting AF biasing routines into the operational menu. The K20 allows for fine tuning the AF for up to 20 lenses. Check your owners manual for how to do it.
Be aware that with a zoom lens of this wide a range, you will probably not get accurate biasing (an consequently, accurate AF) across the entire zoom range.

Shake reduction does not equate to shake elimination. If you want sharp pictures, especially with a long telephoto, use a tripod.

The K20 sensor is some 40% higher resolution than the K10 sensor. What looked good on a K10 may not be good enough to look good on a K20.
Sending your camera in with a third party lens attached isn't going to do you any good, since Pentax is not in the business of supporting off brand equipment.

Adjust the AF bias before you blame the camera.
06-10-2008, 12:10 PM   #8
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To check FF/BF problems,download a focusing chart on Google and follow the instruction on the chart. It' very straightforward and easy. There is one published by Yvon Bourque that I wouldn't use. To many lines on it that can confuse the auto focus. Just remember the 18-200 lens is not the sharpest lens on earth, but you likely have a focusing problem. You should try to post some pictures with EXIF data so we can more accurately diagnose the problem. If you can see any part of the pictures that are sharp (especially if you weren't focusing on that part), you likely have a focusing problem. Less often encountered, the AF might not be looking at exactly the same place as the AF indicatoer in the viewfinder.

06-10-2008, 12:22 PM   #9
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I agree with Michael.

Once Tamron went plastic and started slapping the SP badge on whatever, their quality has gone way downhill.
06-10-2008, 01:15 PM   #10
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QuoteOriginally posted by Wheatfield Quote
The K20 sensor is some 40% higher resolution than the K10 sensor. What looked good on a K10 may not be good enough to look good on a K20.
Sending your camera in with a third party lens attached isn't going to do you any good, since Pentax is not in the business of supporting off brand equipment.

Adjust the AF bias before you blame the camera.
be careful 40% increase in pixels does not mean 40% increase in linear resolution! Actually the increase is somewhat less than that, I believe about 19%

Your point is noted however, as the pixel count goes up, pixel peeping will possibly show more fuzzy lines, but, if you print to the same size as before, you will not see the difference, it is only if you blow it up more.
06-10-2008, 02:20 PM   #11
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QuoteOriginally posted by NicholasN Quote
I have owned my K20D for a little over a month now.

Originally I bought a Tamron 28-300mm LD IF Super Zoom lens. It failed to correctly focus at long focal lengths and didn't produce the clarity I was looking for. I sold that recently and purchased a Tamron DiII 18-200mm zoom.

Again, the K20D has trouble auto-focusing correctly and regularly gives me shots where the focus is nothing to be proud of.

Now I know for a fact the lenses are well proven and have good reviews. I can now only deduce the K20D body is possibly faulty, or that I am expecting too much clarity from a 15MP camera and that I have to be SUPER careful that I am holding the camera perfectly still even at very fast shutter speeds.

My K100D would produce fantastic crisp shots even with the worst of camera shake and no SR active at 1/400 and over on moving targets.

The K20D gives quite blurred shots even with SR turned on and shutter speeds in excess of 1/750.

What should I do? Lose my camera for possibly weeks or months and have it sent back for testing or is this just par for the course with this body?

Nick, I followed your other Tamron/air show thread. It sounds like there may be an issue with your K20D if you're not getting the shots with it that you got with your K100D. I've owned both, and I get the same shots with my K20D that I got with my K100D, so I don't think the K20D is inherently harder to use.

I hate doing brick wall tests and such, but have you tried any controlled tests to see what conditions work and which don't?
06-10-2008, 06:45 PM   #12
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I am mostly intrigued by the occasional way front focus, that is not in line with any of the other shots and led me to some pretty soft shots (even with the 40/2.8 or 16-50/2.8), it also helped me to some wrong conclusions regarding the AF adjustment, and am right now at 0 again, I either figure out what is wrong (me? ) (lower lighting and/or flourescent seems to be the common denominator), if not it will go to Pentax to have them give it a physical after an event i need the camera for.
If there were at least subjects close to the center focus point that i could say "Ah, ok, that must have confused it.", but that's never the case.

I'm trying to say the results from the K20D are great with a good lens (Go Go Takumar Power!), with some occasional drop outs that seem rather inexplicable.

On a 18-200, see if adjusting focus in the 50-150 range works, closer to 18, use it at f/8 or more stopped down, and try to avoid the extreme tele end if you do pixel peep, neither extreme/end of a super zoom is going to be pleasing.
06-11-2008, 04:45 AM   #13
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Aside from the obvious point that the OP has not yet posted an example, we seem to be headed into another discussion about an issue that everyone talks about but I am not sure everyone understands.

I now see the dreaded focusing charts being mentioned, and , I'm sure, another round of discussion about the results.

FOcusing charts are the biggest problem with the front focusing issue, because so few people use them correctly.

In order to make sure we don't go back down the wrong path, please note the following.

The charts are to be used at a 45 degree angle, and the camera is to be set level with the center of the chart, and the axis of the lens at right angles to the chart centerline. This is best achieved if the camera is mounted level on a tripod, and the chart is moved away from the camera, and set at an angle.

Also please note that depth of field is NOT linear. In fact, if focused correctly on the centerline, the range of acceptable focus on the chart is 1/3 in front of the line, 2/3 behind the line. This causes many to believe the lens back focuses when it does not.

Please also note that the exact location of the focusing sensor can have a large impact on these results, as does slight vertical misalligmnebt of the target on the sensor, That is why hand held shots can be so far off. You need to be very careful, and I would suggest trying the shot at all 4 camera positions including upside down (or slanting the focusing target the opposite way), focusing always on the same spot.

Then let's see the results

By the way, have I mentioned the OP has not yet posted examples
06-11-2008, 08:08 AM   #14
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QuoteOriginally posted by Lowell Goudge Quote
Also please note that depth of field is NOT linear. In fact, if focused correctly on the centerline, the range of acceptable focus on the chart is 1/3 in front of the line, 2/3 behind the line. This causes many to believe the lens back focuses when it does not.

Please also note that the exact location of the focusing sensor can have a large impact on these results, as does slight vertical misalligmnebt of the target on the sensor, That is why hand held shots can be so far off. You need to be very careful, and I would suggest trying the shot at all 4 camera positions including upside down (or slanting the focusing target the opposite way), focusing always on the same spot.
Which is why i don't print out test charts, and just use the camera, and judge the results with "hm, i should have gotten that shot."
But yeah, it could be another thread where the OP long abandoned the problem and we all just chime in anyway
06-11-2008, 06:56 PM   #15
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QuoteOriginally posted by Lowell Goudge Quote
Please also note that the exact location of the focusing sensor can have a large impact on these results
what can one do about this? If the focus dot isn't in the right place what hope have we got!
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