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10-18-2009, 08:01 AM   #31
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I send a email to Pentax and they said I need to send it to them with the lens and they would give me a price on the repair, I've never sent anything in before and not sure If I want to send in my Tamron 17-50 lens.

10-18-2009, 08:31 AM   #32
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QuoteOriginally posted by Class A Quote
Nonsense!

There is a disadvantage associated with DSLR AF which is that if there is misalignment between the sensor and the AF system, there will be misfocus. But a properly calibrated camera does not have that problem.

Another potential problem is that the AF system sees something else than the sensor (due to colour temperature -> a problem the K-7 no longer has, or due to spherical aberration).
Not my words but I interpreted this based on the fact that drive motors (not sure of the ultrasonic) were steppers... there could be a "gap" , especially at large apertures or short throw lenses where either step is wrong (forward or back). Then the AF algorithm has a "best case" and "give up" mechanism. Of course this does also apply to "live" af as well. Add mechanical "slop" and my point was we are lucky it's even this good
I cannot find any logic in assuming that it is just a AF to sensor baseline adjustment is the only (or major) cause of AF adjustments. It can not explain lens to lens variations or same lens zoom variations in focus...there must be some other cause. The large aperture/larger baseline sensor is one solution to a problem unrelated to any "distance" problems.
color dependencies are known (Canon can misfocus in fluorescent lighting, Pentax in tungsten).
spherical abberaton problems w/ change in f stops seems to be more of an issue then any AF mechanical baseline errors..
Autofocus camera - US Patent 4890133 Description
Canon does run some open loop AF that is predictive. Which is why they can get the speed out of it.
http://doug.kerr.home.att.net/pumpkin/AF_accuracy.pdf
Canon AF System
Operation

When you half-press the shutter release (or the * button, if you've used the custom function to move focusing control there), the activated AF sensor "looks" at the image projected by the lens from two different directions (each line of pixels in the array looks from the opposite direction of the other) and identifies the phase difference of the light from each direction. In one "look," it calculates the distance and direction the lens must be moved to cancel the phase differences. It then commands the lens to move the appropriate distance and direction and stops. It does not "hunt" for a best focus, nor does it take a second look after the lens has moved (it is an "open loop" system).

If the starting point is so far out of focus that the sensor can't identify a phase difference, the camera racks the lens once forward and once backward to find a detectable difference. If it can't find a detectable difference during that motion, it stops.

Although the camera does not take a "second look" to see if the intended focus has been achieved, the lens does take a "second look" to ensure it has moved the direction and distance commanded by the camera (it is a "closed loop" system). This second look corrects for any slippage or backlash in the lens mechanism, and can often be detected as a small "correction" movement at the end of the longer initial movements.


Now to the OP I think a simple recalibration of the K20 is called for but my point was don't expect it perfect for all lenses all the time....... considering ALL the factors that go into AF-ing
10-18-2009, 08:41 AM   #33
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QuoteOriginally posted by Fl_Gulfer Quote
I send a email to Pentax and they said I need to send it to them with the lens and they would give me a price on the repair, I've never sent anything in before and not sure If I want to send in my Tamron 17-50 lens.
Wasn't more than one lens off? If you calibrate to the Tamron this may cause problems w/ new lenses but if it's your primary, it may be best to send it in w/ the body. Pentax is in a rock and hard place situation (which most people fail to see)
Just insure it well.
10-18-2009, 09:34 AM   #34
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QuoteOriginally posted by Class A Quote
The precision of the tilt is not critical at all. Any angle that allows you to see the change in sharpness will do.

It is, however, critical to make sure you focused on the middle focus target.
Right, and that's the main reason to not use *too* steep of an angle, or the text above or below below the target will come into range of the AF sensor. That *might* have happened here, and although I suspect not, it's definitely worth repeating the tests in more balanced light (fluourescent bulbs vary widely in temperature during the 60Hz cycle and could also be playing havoc with the AF system) and with more care to the shooting angle. Don't worry about making if 45; just make sure the text above and below don't get range of the central focus sensor (which extends more or less to the top and bottom of the inner bracket on the focus screen, maybe a bit further).

*Definitely* repeat this test - in more controlled lighting, better angle, and also comparing to other lenses - before sending anything in for repair.

10-18-2009, 10:24 AM   #35
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The K100D shot has sharpening artifacts around the text on the box. The K20D shot does not.

What are you using for post process on your photos?

Also have you tried micro adjusting for this lens? I thought the K20D could be adjusted for a number (10? 20?) lenses?
10-18-2009, 11:26 AM   #36
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The photo's were right out of the cameras and unprocessed. I'm not sure if after you click the photo's that you can click them again to resize to a larger size. Then you can see the difference in shots.

I use 3 lenses with the camera and I use them all about the same time.

Tamron AF 17-50mm 2.8
Sigma EX 105mm 2.8 Macro
Sigma EX 100-300mm 4.0
and I'm not sending them all. we do have a photo repair & sales shop that deals with all DSLR's (Even Pentax) in the neighboring town. I could take my whole set-up to them and see what they say about correcting it.???
10-18-2009, 11:44 AM   #37
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The point i was trying to make is that there has been some sharpening added to the K100D photo, that has not been added to the same extent on the K20D photo.

If you are shooting JPEG's from both cameras, do you have the same sharpness, contrast, etc. set the same for both cameras?

Also Have you used the Auto-focus adjustment? Page 106 of the manual? It looks like you can adjust up to 20 lenses?
10-18-2009, 12:14 PM   #38
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I just checked both cameras and no adjustments have been made in the custom setting, no sharpning.
I just used the dust removal in the k20d and now the focus seems to be much closer than it was before. I can hardly tell that the AF is off on the Tammy 17-50 and it seem about +2 off on the Sig 105mm. so maybe my sensor is loose or something. I'm real confused now.

10-18-2009, 01:57 PM   #39
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QuoteOriginally posted by jeffkrol Quote
Not my words
Yes, I know, but I didn't know how to indicate that without getting lengthy.

QuoteOriginally posted by jeffkrol Quote
Of course this does also apply to "live" af as well.
Exactly. If the focusing mechanism is based on open loop control you've got the problem with sensor based AF as well. To the best of my knowledge Pentax AF uses closed loop control.

QuoteOriginally posted by jeffkrol Quote
I cannot find any logic in assuming that it is just a AF to sensor baseline adjustment is the only (or major) cause of AF adjustments.
That's why I provided other sources of errors. The apparent f/5.6 aperture at which the AF systems "sees" is probably one cause for AF problems with lenses that have a pronounced focus shift due to aperture change.
10-18-2009, 02:02 PM   #40
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QuoteOriginally posted by Fl_Gulfer Quote
I just checked both cameras and no adjustments have been made in the custom setting, no sharpning.
Have you also checked the JPEG settings such as "bright" vs "natural" and all the "contrast / saturation / sharpness" settings? Note that even if you use the same settings, the cameras probably interpret them differently, i.e., "neutral" sharpening on the K100D could correspond to "+1" sharpening on the K20D.

There is no denying that the two shots are different in terms of JPEG settings and/or differently resized.

QuoteOriginally posted by Fl_Gulfer Quote
I'm real confused now.
Did you use the same light for the retest? If the light was different (even if you just added daylight to the mix) then it is no surprise that the measurement results are different.

I'm surprised to hear that Pentax wants your non-Pentax lens. Sending in camera + lens makes a lot of sense but so far it has been Pentax policy to only do this for Pentax lenses.
10-18-2009, 08:23 PM   #41
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This time I did the test in natural sun light.
10-18-2009, 09:08 PM   #42
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QuoteOriginally posted by Fl_Gulfer Quote
This time I did the test in natural sun light.
No need to suspect a lose sensor then. The different ligth explains the difference in the focus tests.
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