Sunday, September 23, 2007

DA 21 Mis-Focusing - A Design Problem?

Quite some time ago, I wrote here for the DA 21 Limited Front Focusing (FF) and Back Focusing (BF) problems as reported by some users, in my fourth article in my this blog (and actually the first time for me to talk about the issue on the net - the contents of the first three articles were actually talked about and discussed previously in three different posts at the Steve's Pentax forum which got me banned shortly afterwards overthere).

Later on, the famous professional fashion photographer, Mr. Benjamin Kanarek, who was a new Pentax user (as you know, he switched from Canon), found that his DA 21 Limited lenses as acquired from Pentax France/Germany were having back focusing and also front focusing problems and he finally got four copies of the DA 21 after that I have not seen that he reports again about mis-focusing of his DA 21 on his K10D anymore. Nonetheless, I'm not sure if his this copy really works for him now or he has just aborted to try as the problem might still persist.

So, reports of those FF and BF problems of the K10D, in particular for those associated with the DA 21 Limited which are even more frequently reported, either with the K10D or the K100D or both, just have been continuing to appear up till now (yet an recent example here, with comparison photos posted). Recently, particular German users have found that the mis-focusing actually associated and being affected by the aperture f-number as set by the user or as selected by the camera, which a German user summarises the case clearly and precisely in the following DPR forum thread:-

http://forums.dpreview.com/forums/read.asp?forum=1036&message=24445741

So, the reported strange phenomenon is that if the aperture selected is smaller than f/5.6 (i.e., f/6.3 and onwards), the AF accuracy will be better, even if the user set a f/8 value first, say, then performs the AF, and then change the f-number back to f/3.2 wide opened, say, and take the shot - the focus achieved is usually better than when the user uses the camera normally, e.g., f/3.2 is selected when doing the AF and then take the shot at f/3.2.

Indeed, the above finding really sounds very strange and odd and I could hardly believe that for the first time I heard about it. However, by following down the above DPR thread, one will not be difficult to see quite some different DA 21 users have confirmed the same phenomenon after they tried and tested their gear, no matter briefly or extensively with care. So, the strange problem, along with the yet clumsy and odd "workaround", have been confirmed.

Actually, I saw before from an issue (#116) of a local magazine that the resolution of the DA 21 lens on a K10D as tested and measured using the Imatest is rather low, with results not more than 1,600 LW/PH (Line Widths per Picture Height) at image centre and around 1,400 only at image corners, at best. To compare the figures, I checked the Issue 115 of the same magazine for the test results of the (just 6MP) Nikon D40 with (just) the Nikkor kit lens 18-55 II AF-S and was rather surprised to learn that at 18mm, it yields results at about 2,100 LW/PH at image centre and about 1,500 to 1,600 LW/PH at the image corners, depending on the f-stop used, which simply means that the resolution of the kit lens on the D40 just blows away the DA 21 Limited prime on the K10D fully and also throughout the whole picture frame as well !(?)

Well, the possible reasons for the low resolution as verified above can be two: 1. The inaccurate AF system of the K10D which gives mis-focusing which in turn decreases the effective resolution significantly; 2. Blurry in-camera jpegs of the K10D (first discovered and reported by Phil Askey) which are primitively having lower resolution than other DSLRs of the competitors or even the K100D (now it is worse than the D40, as verified in the mentioned tests above, in just two consecutive issues of the same bi-weekly magazine).

As a side issue, a poster who responded to the above DPR thread also pointed out that the final focus point achieved by the AF system of his DA 21 varied depending on whether the lens was turned from infinity or from the closest position, which this yet strange but surely undesirable phenomenon was first reported by me nearly two years ago in my this post in 2005. It was really rather disappointed that now the DA 21 on the latest Pentax DSLRs is still the same, with the same old problem, even after two years I had reported the issue.

Do note that in my above old report I had indeed fully tested my $180 MZ-30 (and my more expensive MZ-S too) that my FA 43 Limited did have NO such problem exhibited on these two film bodies whereas my *ist DS and D are having the mentioned problems obviously and do note also that I tested and compared the MZes and the *ist Ds at the same environment, with the same FA 43 Limited lens, for the same target(s) and at the same time. So, this case is really rather sad and absurd.

All in all, I really don't understand why the problem is still here and it seems that Pentax have not listened and still don't listen and the bug is still here! (but Why?) The Bottom line is: Don't forget that the MZ cameras do NOT have similar problems! (including the rather cheap $180 "bottom-of-the-line" MZ-30). So the key point still is: IF Pentax listens.. (and also if They didn't produce inferiorly performing systems in their DSLRs, namely, the AF and AE systems used, which they did do it right and were capable to make better stuff before, in their MZ line of film SLRs..)

See Also:-

AF's Dependency on Lenses and Yellow Light

Focus Calibrations of Pentax DSLRs and Lenses

14 Comments:

Anonymous said...

It is a unique, extremely compact prime, so I would give it a bit more leeway in any downsides, but I agree it should not have consistent focus problems.

You should be more accurate in your rants though, K10D jpegs are not "blurry", they just aren't edge sharpened to the same degree as other cameras. "Soft" maybe. Means the D40 is a better camera than the D200 in your book.

RiceHigh said...

I don't know if the D40 is better than the D200 or not. I only know the resolution as measured by the above mentioned magazine for those Imatest Spatial Frequency Response resolution tests that the K10D with the DA 21 combo yields (much) lower resolution figures than the 6MP D40 with a kit lens on it (compared to the 18mm of the kit lens).

So, no matter what you like to use in describing the "characteristics" of the K10D jpegs, it surely doesn't give the user the high resolution as expected and as it should be.

Anonymous said...

Focusing comments aside: Pop Photo seemed to like this lens:
http://www.popphoto.com/cameralenses/3478/lens-test-pentax-21mm-f32-da-af-limited.html
And Klaus had much higher resolution numbers than you report:
http://www.photozone.de/8Reviews/lenses/pentax_21_32/index.htm
"The center performance is exceptionally high whereas the borders require f/5.6 to achieve very good levels"
Your Pentax hatred is showing again... ;)

lol101 said...

Well, as an impartial blogger that gives unbiased information about Pentax misdeameanors, you should also cite some figures from another online site which tested the 21 and the Canon lens you mention.

I'll give the figures for the sake of completness:
Canon 18-55 @ 18mm/f3.5 center: 1679 lpm, corners: 1120lpm (@f5.6: 1820/1263 lpm)
Pentax DA 21 @f3.2, center: 2162lpm, corners: 1537lpm (@f5.6: 2290/2012lpm)

There ya go...

It's a nice "Fox News style" blog on Pentax you have here...

RiceHigh said...

> Anonymous said...
> Klaus had much higher resolution numbers than you report

Don't you know that: 1. Klaus checked for the best possible highest resolution chosen amongst different pictures that focused manually and automatically for the best focused picture? 2. He shot in RAW and converted via ACR, but not anything in-camera nor via any original Pentax stuff. Do you know?

RiceHigh said...

> lol101 said...
> Well, as an impartial blogger that gives unbiased information about Pentax misdeameanors, you should also cite some figures from another online site which tested the 21 and the Canon lens you mention.

When did I and where do I mention the Canon kit lens??

Anonymous said...

What a stupid blog. Pentax AF is no worse than my Canon 5D. Sure my 5D is better, but having graduated from a Pentax K10D you are absolutely wrong in your assement of inaccurate AF on the K10D.

Do not try to be an expert as you are just rehashing a bunch of opinions from other losers like yourself trying to look important. I am not a fan of Pentax and probably never buy another camera from them as I need access to multiple lenses that Pentax cannot deliver. To say inacurrate AF on their systems without a shred of proof (Your entire blog has no facts by the way) just shows you do not know what you are talking about. If you hate Pentax so much, dump your equipment and Buy Canon. Stop your sniveling child like behaviour and learn to take pictures.

Anonymous said...

He already bought Canon but just won't go away. I can think of some similar "rashes" ;)

Anonymous said...

Leave Ricehigh alone, just because he is the equivalent of a loud mouth anal-retentive mechanic who can't actually drive a car himself doesn't mean he's always wrong!

Would you trust a mechanic that just backed his car into a post trying to park?

Anonymous said...

"Nonetheless, I'm not sure if his this copy really works for him now or he has just aborted to try as the problem might still persist."
You'll be happy to know it works just fine I hear.See Rice,thats your problem, you should have said something like "Nonetheless, I'm not sure if his this copy really works for him, he has just aborted to try as the problem might still persist or that he now has a working copy. MAYBE I should check and report back to you"
SEE how easy it is...and if he got a 4th bad copy, then say some more swarmy comments. And yes 4 copies to get a good one is not a good thing BUT apparently good copies exist so it may not be a "engineering" problem, just poor QC or maybe not... speculate and expound all you want, your biased to the hilt against Pentax.. ;)LOL

RiceHigh said...

So, how about the reports by the other DA 21 owners? Do you want to ignore all those just because what is reported is again "unfavourable"??

Anonymous said...

You ignore all the good reports so ignoring all the bad seems justified in your way of thinking.....
:)

Anonymous said...

I don't have much of an opinion on this topic. I have the 21 Ltd and it is quite the fine lens. Perhaps others have bf/ff issues. My only comment is that this blog genuinely cracks me up. LOL! RH, all this heated, sometimes witty and never boring banter back and forth with your readers is really quite entertaining. HILARIOUS! I LOVE IT!!! Please keep on doing what you do.

roentarre said...

Da 21 ltd does mis-focus when subject is close to the lens.

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