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03-16-2008, 01:20 AM   #1
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Improved AF Accuracy of the K20D (Under White Lights Only)

Since Frank hasn't shared his results and findings here but just at the DPR (pls correct me if I'm wrong), here is my report to share:-

An experienced Pentax DSLR user, who has a bundle of Pentax AF/digital lenses and various Pentax DSLR bodies including the K100D, K10D and the new K20D, has tested and compared (side by side) the AF accuracy between his K10D and K20D with different higher grade Pentax fine lenses of his putting on both bodies:-

K20D AF Accuracy Improvement Over K10D/K100D [Page 1]: Pentax SLR Talk Forum: Digital Photography Review

First of all, here is his detailed comparison tests (two sets - will explain more below) regarding the AF accuracy differences with the DA 21 Limited lens on K10D against the K20D, pair of comparison test shots are posted:-

K10D+DA21 vs K20D+DA21 (15x imgs): Pentax SLR Talk Forum: Digital Photography Review

Do note that since the DA 21 was found to have strange focusing behaviour on the K10D that the focusing accuracy actually depends on the Av number selected (as well as if the lens is turned from the infinity or closest), which I have reported here before, the user also carried out a second batch of the test in the above to compare the focus accuracy of the K10D against the K20D under the procedure which he believed his K10D should work best.

Well, as it is mentioned in the user's opening post and can be seen from the above detailed tests and measurements, there are significant focusing errors with the K10D whereas with the K20D could do very well with the same DA 21 (and other various Pentax AF lenses he has as well, as told - so far he has not posted all the test photos with all different lenses in the thread, though).

Indeed, I was a bit susceptible on his report when I first read his opening post just because usually people would have some kind of honey moon period effect when they've received their new toys and usually think that the new toys are better (maybe just because they've got excited or actually time will tell for many things, when they use their "new" gear longer). However, since there is some solid measurbation evidence shown above, I think I should believe.

In fact, I am really glad and pleased that Pentax have improved their design finally (as it seems to be from judging from the above) after years of the same persistent AF problem for inaccuracy, at last. I do think that "late is just better than none"!

Well, I do believe that it is always a good thing to let Pentax and the public know about those annoying gear problems as wide as possible so that Pentax should listen and potential buyers/users should be fully aware of such problems as well, before they are sold. Furthermore, for letting more people to know about the problems, more pressure would be made to Pentax so that they are forced to improve to a certain extent, instead of letting the problems drag on for long or even forever! That's is in fact my clear objective in setting up and updating my this blog.

Now, have all the AF accuracy problems (just say for shooting static objects only) been resolved totally? So, what are some of the well-known problems? Just read back my early Blog article about the "AF Accuracy's Dependency on Lenses and Yellow Light", then you will know more about these.

On the other hand, here comes the bad thing as reported also by the above Pentax user who carried out also the test to verify if AF accuracy has been improved under the yellow lights, i.e., tungsten light source or any artificial light source with low colour temperature. Unfortunately, he found that obvious Front Focusing *still* occured, as always for ALL Pentax DSLRs:-

K10D and K20D under tungsten/fluorescent light: Pentax SLR Talk Forum: Digital Photography Review

This is yet a disappointment, although I would not be of big surprise. In contrast, I have been surprised this time for what it has been proved that one of the most annoying "Pentax's" problems has actually been removed, with the K20D.

Since I shoot a lot under tungsten lightings which are often dimmer conditions, I had found that such AF system problems to be a big annoyance. This is in fact one of the main reasons that I was forced to get a Canon 5D kit in June last year. Later on, I got also the Canon 50/1.8 fast prime which I have never seen the Yellow Light Symptom of the Pentax DSLRs (which I was the very first person on the Net to conduct a quick experiment to verify this problem), even at fully wide opened and under very dim conditions and even with low contrast objects. More importantly, the focusing was still fast and decisive with the 5D at lower light conditions, unlike all other Pentax DSLRs that would hunt seriously in the same conditions. Moreover, do note that Pentax film AFSLRs like the expensive MZ-S flagship and the entry level model MZ-30 which I have both do not slow down like what the Pentax DSLRs would do under lower light conditions, neither. Nevertheless, the MZ cameras do shift a little bit with slight front focusing under tungsten lightings but the magnitude is not that large as those Pentax DSLRs - that I can tell - just believe it or not!

A few days before, I tried two units of the K20D, I am not overall impressed with the AF responsiveness of the K20D neither. That says the K20D required to think longer than I would expect for the AF motor start to move and it also need longer time to re-confirm the focus and re-adjust the lens as well. This slow responsiveness that I can feel easily is not really a good thing, IMHO.

Last but not least, here are the remaining posted test results (a few pairs of shots only) for the AF accuracy comparison between the K10D and the K20D with a few other different lenses which the above mentioned user has, which proves again the AF accuracy of the K20D has improved whereas the AF accuracy of the K10D is just rather poor:-

K10D vs K20D w/ some other lenses: Pentax SLR Talk Forum: Digital Photography Review

So, for those old Pentax DSLR users who have being wanted to upgrade just because of the particular deficiencies they don't like and ask me if it worths the upgrade to the K20D by now. My answer would be "Nope" at the current stage, undoubtedly. It is just because I won't spend another (US)$1,400 to cure only one of the long lasting and well known problems which exist mainly in all the previous models of Pentax DSLRs. Unless later on it can be confirmed that more of the old typical Pentax problems for the camera performance and accuracy aspects are cleared (like this time for the AF errors with different lenses), it is just too risky to put the bet *now*, I would say. Note that for $1,400, actually we could already invest into a few good lenses in the basic focal range for another better system, even if we are to start from scratch, like what I did last year (although these glass may not be as good as some of the original Pentax glass! ;-))

Original article with all the quoted URLs contained:-

RiceHigh's Pentax Blog: Improved AF Accuracy of the K20D (Under White Lights Only)

P.S. My special thanks to Frank for the great tests carried out and for sharing on the Internet to let us Pentaxians to know too!


03-16-2008, 12:04 PM   #2
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yada, yada, yada...blah, blah, blah...
03-16-2008, 12:19 PM   #3
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"us Pentaxians"? This from an avowed Canon disciple? Give me a break.

I have been here less than a year, and I have not seen anything from this poster that has any merit or purpose other than to create controversy. Isn't that the definition of "trolling?' He is again using this forum to promote Canon, and DPReview, and to spread his misinformed bias against Pentax.

Mods, please help us out here, and send this OP packing.

Last edited by PentaxPoke; 03-16-2008 at 12:27 PM.
03-16-2008, 03:11 PM   #4
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Just finished testing...

my 2 weeks old K20D for focus accuracy. Although images were more or less on par with my K10D (which I already managed to sell happily due to numerous small bothering problems with it) but not as crisp as my K100D. I had given up handheld macro with K10D some 9 months ago using K100D happily for it :-) Now first macros with K20D- and same story as with K10D :-( OK, did a 45 degree test chart setup with bright primes- and all of them needed correction of -10 units :-( Proceeded to zooms and although apertures are smaller and DOF is not so shallow and differences harder to detect- still -10 was the best. Ran out of time but seems that with my (unlucky) body (again) I have to set overall focus adjustment to -10 units and then run the next round of tests at least on primes to be a happy camper again. So my question- does anybody know if the units for adjustment are the same for overall body and individual lens (I mean they are added to each other in the simple way)?
BTW Remote Assistant was of great help for this job :-) Pentax has improved it in several ways: You can leave SD card in body, You can use shutter knob if desired etc. Rather impressive but would like to have a complete Custom Menu in it- at the moment I was missing AF adjust menu on screen- that would make the testing/adjusting a pure pleasure :-)
Best and happy shooting and aint whining, JR

03-16-2008, 06:53 PM   #5
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Rice...Go Away...Thank you.
03-17-2008, 05:25 AM   #6
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QuoteOriginally posted by jgredline Quote
Rice...Go Away...Thank you.
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Be quick to listen, slow to speak and slow to anger...
Thx,
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Pls be "quick to listen, slow to speak and slooow to ANGER".
03-17-2008, 05:28 AM   #7
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Replace it or ask servicing

I suggest you to get your new K20D replaced/returned) if possible since that your copy seems to be mis-calibrated. If it is not possible, just ask Pentax to re-calibrate it. As Frank has been able to get a K20D which focuses quite well with good accuracy with different lenses whilst his K10D and K100D are not, I do believe the K20D does have an improved AF system. If your found problem with your K20D is not a design fault, it should be easily cured (of course by Pentax, as it is needed).


QuoteOriginally posted by Reps Quote
my 2 weeks old K20D for focus accuracy. Although images were more or less on par with my K10D (which I already managed to sell happily due to numerous small bothering problems with it) but not as crisp as my K100D. I had given up handheld macro with K10D some 9 months ago using K100D happily for it :-) Now first macros with K20D- and same story as with K10D :-( OK, did a 45 degree test chart setup with bright primes- and all of them needed correction of -10 units :-( Proceeded to zooms and although apertures are smaller and DOF is not so shallow and differences harder to detect- still -10 was the best. Ran out of time but seems that with my (unlucky) body (again) I have to set overall focus adjustment to -10 units and then run the next round of tests at least on primes to be a happy camper again. So my question- does anybody know if the units for adjustment are the same for overall body and individual lens (I mean they are added to each other in the simple way)?
BTW Remote Assistant was of great help for this job :-) Pentax has improved it in several ways: You can leave SD card in body, You can use shutter knob if desired etc. Rather impressive but would like to have a complete Custom Menu in it- at the moment I was missing AF adjust menu on screen- that would make the testing/adjusting a pure pleasure :-)
Best and happy shooting and aint whining, JR
03-17-2008, 06:18 AM   #8
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03-17-2008, 06:18 AM   #9
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QuoteOriginally posted by Reps Quote
my 2 weeks old K20D for focus accuracy. Although images were more or less on par with my K10D (which I already managed to sell happily due to numerous small bothering problems with it) but not as crisp as my K100D. I had given up handheld macro with K10D some 9 months ago using K100D happily for it :-) Now first macros with K20D- and same story as with K10D :-( OK, did a 45 degree test chart setup with bright primes- and all of them needed correction of -10 units :-( Proceeded to zooms and although apertures are smaller and DOF is not so shallow and differences harder to detect- still -10 was the best. Ran out of time but seems that with my (unlucky) body (again) I have to set overall focus adjustment to -10 units and then run the next round of tests at least on primes to be a happy camper again. So my question- does anybody know if the units for adjustment are the same for overall body and individual lens (I mean they are added to each other in the simple way)?
BTW Remote Assistant was of great help for this job :-) Pentax has improved it in several ways: You can leave SD card in body, You can use shutter knob if desired etc. Rather impressive but would like to have a complete Custom Menu in it- at the moment I was missing AF adjust menu on screen- that would make the testing/adjusting a pure pleasure :-)
Best and happy shooting and aint whining, JR
Not sure if it helps but I would suggest you cal your K20D with FA35/2 and some near infinity flat target (like a building, or a tree against plain sky). Set the lens to closest distance then let the camera to AF. Repeat this at least 2 times for each setting and do a few different um settings and see which produce the sharpest results. The tests must be done on tripod with 2s timer and wide open. Don't use chart for cal. I have used this method to cal my DS with great precision with all my lenses. Any close distance cal using chart or anything similar were a complete waste of time based on my experience. Good luck.
03-17-2008, 06:36 AM   #10
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QuoteOriginally posted by wlachan Quote
Not sure if it helps but I would suggest you cal your K20D with FA35/2 and some near infinity flat target (like a building, or a tree against plain sky). Set the lens to closest distance then let the camera to AF. Repeat this at least 2 times for each setting and do a few different um settings and see which produce the sharpest results. The tests must be done on tripod with 2s timer and wide open. Don't use chart for cal. I have used this method to cal my DS with great precision with all my lenses. Any close distance cal using chart or anything similar were a complete waste of time based on my experience. Good luck.
I partially agree for what you say, Alan. Testing AF at close distance is not a waste of time but shooting a "45 degree" test chart surely is.

Shoot a flat surface, which has a plane perpendicular to the optical axis of your lens, like my this example:-

Pentax *ist DS AF Dependency on Kelvin & Exposure Value
03-17-2008, 06:39 AM   #11
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QuoteOriginally posted by ftpaddict Quote
It's not being angry, it's being fed up.
I do appreciate his slogan.

Quick to listen: Right - so that we can learn.

Slow to speak: Right - so that we can make sure the facts before we speak out.

Slow to anger: Yes, surely!

So, btw, what's meant by "being fed up"? Sorry for my poor English ability. Grateful if you could explain a little bit more for what you actually meant.
03-17-2008, 07:03 AM   #12
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Well the K20D AF Accuracy is better than the Canon 40D I shot with in the bar scene so scratch it as better than Canon in mixed lighting RH. Would you like numbers? I had 15 in focus Canon shots to 40 OOF (this is critical focus) and 75 in focus Pentax shots to 112 OOF. The light in the bar being a mixture of tungsten, fluorescent, neon and halogen.
03-17-2008, 07:36 AM   #13
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RH I have pledged long ago to never respond to your threads. I was board and decided to today.







03-17-2008, 09:19 AM   #14
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QuoteOriginally posted by vievetrick Quote
RH I have pledged long ago to never respond to your threads. I was board and decided to today.








Agreed.........
03-17-2008, 09:20 AM   #15
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Hi Rice, and THanks for the post/info.
Though some are quick to dismay anything you say I do listen, but re-conferm with my own experence/tests.
As of now I have not found the lack of difference in AF with my K20D yet, esp with my FA* 300mm F2.8, I will still be testing. I have found AFC to be better on the K20 so fay and it seams to be quicker in low-light with my FA 50mm F1.4.
thanks
PS. Everyone... let everyone express findings that they have had. sure if they are prur-bashing the moderator should take care of them, but respectifuly disagree if you mest so. We dont want this place to become like DPR
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