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08-26-2013, 01:20 PM   #1
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DEBUG Testing

Since I have purchased a K5, I am going to use my K200d as a test bed for MODSET.445 and PK_Tether for DEBUG experimentation, but first a few words about the K200d!
All my lenses for this model have been Sigma or Tamron brands except for one Pentax 50mm 1.7 A model. Two Sigmas are AF; all others, including one Sigma, are MF. Every lens of either the AF or MF type required tweeking via MODSET to get anywhere near optimum focus, especially in low light. This seems to be a known bug-a-boo with the K200d. Now with my K5 and the new Sigma 50mm f1.4 EX DG teamed as my every day tool, I don't mind the risk of using the K200d as a test bed to explore the full range of DEBUG options.
In open daylight, the K200d is, and has been, a very satisfactory performer within its specification constraints. If anyone has any comments or suggestions to add for my consideration, I welcome your 2 cents!

08-26-2013, 03:12 PM   #2
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The K200D in debug has only limited possibilities to adjust AF focus (which automatically works also on the green hexagon you can use as a help function for MF lenses). And using the green hexagon as a help for this adjustment could really start messing it up, as this confirmation has quite a big hysteresis.
The adjustment can, within limits, compensate for inadequate thickness of the shim of the viewfinder screen, and for slightly misaligned position of the AF sensors. However, compensating shims this way is not really a good idea, as visual sharpness in the VF is not changing, and will still be misleading.
Compensating for AF sensor positions may be successful, but will depend on the kind of misalignment.

But AF errors are often caused by wrong numerical translation of the move command from body to lens, which is done by a chip inside then lens. After all, the AF mechanics of 3rd party lenses will be the same for all brand adaptations, but the command by the body to adjust focus may be completely different for each camera brand. Sigma/Tamron/Cosina don't own Pentax licenses and are working with reverse engineering. And the data base for the translation in the lens chip must probably be calibrated differently for each lens copy.

I think the problems I hear from many users are caused by their attempt to compensate such lens mis-calibration by in-body AF focus adjustment. This is possible, but it will be absolutely correct only for one distance (and, with zooms, only for one focal length). But the worst is, that you are compensating a lens error by causing a reverse camera error. If you do this for a prime and are lucky, you may get rid of mis-focusing with that lens - but most likely this will not help with other lenses, and may well worsen the situation with lenses which are correctly calibrated.

There is a reason why lens manufacturers always want to get both lens and body for lens calibration. They must first remove the mess users started with in-body adjustments, before they can start to make lens calibrations.

When everything was out of control after I changed the screen in my K200D to a Chinese one, I first tried to get my SMC-A 1.4/50 spot on at F1.4 by correct shimming. Only when I was sure this was ok, I started to adjust AF in debug mode. Probably just a random result, but the AF adjustment was nearly exactly equal the needed difference in shim thickness. After this procedure, AF and MF was correct with all my many other lenses, too.

Last edited by RKKS08; 08-26-2013 at 03:55 PM. Reason: Infos added
08-26-2013, 05:13 PM   #3
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Original Poster
QuoteOriginally posted by RKKS08 Quote
The K200D in debug has only limited possibilities to adjust AF focus (which automatically works also on the green hexagon you can use as a help function for MF lenses). And using the green hexagon as a help for this adjustment could really start messing it up, as this confirmation has quite a big hysteresis.
The adjustment can, within limits, compensate for inadequate thickness of the shim of the viewfinder screen, and for slightly misaligned position of the AF sensors. However, compensating shims this way is not really a good idea, as visual sharpness in the VF is not changing, and will still be misleading.
Compensating for AF sensor positions may be successful, but will depend on the kind of misalignment.

But AF errors are often caused by wrong numerical translation of the move command from body to lens, which is done by a chip inside then lens. After all, the AF mechanics of 3rd party lenses will be the same for all brand adaptations, but the command by the body to adjust focus may be completely different for each camera brand. Sigma/Tamron/Cosina don't own Pentax licenses and are working with reverse engineering. And the data base for the translation in the lens chip must probably be calibrated differently for each lens copy.

I think the problems I hear from many users are caused by their attempt to compensate such lens mis-calibration by in-body AF focus adjustment. This is possible, but it will be absolutely correct only for one distance (and, with zooms, only for one focal length). But the worst is, that you are compensating a lens error by causing a reverse camera error. If you do this for a prime and are lucky, you may get rid of mis-focusing with that lens - but most likely this will not help with other lenses, and may well worsen the situation with lenses which are correctly calibrated.

There is a reason why lens manufacturers always want to get both lens and body for lens calibration. They must first remove the mess users started with in-body adjustments, before they can start to make lens calibrations.

When everything was out of control after I changed the screen in my K200D to a Chinese one, I first tried to get my SMC-A 1.4/50 spot on at F1.4 by correct shimming. Only when I was sure this was ok, I started to adjust AF in debug mode. Probably just a random result, but the AF adjustment was nearly exactly equal the needed difference in shim thickness. After this procedure, AF and MF was correct with all my many other lenses, too.
Thank you, RKKS08! Perhaps I have planned to bite off more than I can chew....! You have given me information on more aspects of AF focusing problems than I would have imagined. Are you suggesting that a Pentax DSLR should be used with a Pentax AF lens only and this combo will be AF trouble free? Again thank you for your prompt response.
Respectfully,
doc58bc
08-28-2013, 04:42 PM   #4
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QuoteOriginally posted by doc58bc Quote
Are you suggesting that a Pentax DSLR should be used with a Pentax AF lens only and this combo will be AF trouble free?
Certainly not!
If you search through this forum, you will find a lot of users which had problems with AF accuracy of Sigma lenses, but no one can know how many were without problems. And it seems nearly always the problems were gone after sending everything to the Sigma service.

And there are reports also for Pentax lenses which were not ok (it shouldn't happen with the "hand made" limited lenses).

And please keep in mind, that all my suggestions were about bodies which offer a global AF adjustment only. Newer and high end Pentax cameras can memorize adjustment seperately for each lens.

But the K200D does offer only the global adjustment, and it is in the hidden debug mode. That's why I think it was never ment to be used for compensating adjustment faults - not even for the Pentax service. I think this possibility can be used by service for a quick investigation about Af errors with a trusted lens without opening the body (which would probably mean to replace WR seals). Maybe in some cases they can use the values gained to move the zero of the debug AF adjust by writing directly to the ROM.

If I had BF or FF not the same with all lenses, I would never try to adjust by applying a global setting. Also, you would need to have one "trusted" lens to get an idea what is happening.

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