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12-15-2013, 12:56 PM   #1
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My story with firmwares (kept v1.01)

I just going to tell my story: CD-AF on K-01 speed vs. accuracy.

I had no focus troubles with my yellow brick (fw1.03/1.04) and the AF lenses (SX40, F24-50, F35-70, F100 Macro).
I was especially happy IQ wise with the F100Macro. Let me really lowe the K-01.
So ebayed a FA50Macro too. Lens arrived and the horror started.
No sharp shots: maybe 1 from 10, by mistake.
CD-AF can be missaligned -I thought- almost returned the lens to the seller.

As last hope tried fw1.01 (Thanks Pentax letting go backwadrs with fw.versions
And now ALL work as expected, and AF isn't any slower but more accurate with higher keeper rate too.
So -my- conclusion: CD-AF yes CAN BE inaccurate.

The newer fw's may be tweaked for (notable?) speedup but on the expense of accuracy.

For AF I always use tracking, even for static subjects even when no AF-zoom and no focus peaking.
I get consistent the best result this way.

The happy End

12-15-2013, 01:20 PM   #2
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QuoteQuote:
So -my- conclusion: CD-AF yes CAN BE inaccurate.
CD is performed by the sensor which keeps telling the lens to focus until sharpness is met. So I don't quite understand how it can be inaccurate in itself.
12-15-2013, 02:10 PM   #3
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Well, here is the thing.. PD AF can be wrong because sometimes it and the lens are at other ends of their tolerance. This means that it thinks it is accurate, but isn't. So it will consistently back/front focus.
CD AF on the other hand does not have that problem, because it doesn't compare light wavelengths to determine focus. It does, however, rely on a) scene contrast and b) algorithms. This is why fw 1.0 was not as good as the later firmwares - they improved the algorithms for it, and AF sped up! (clearly the hardware remained the same) And it is entirely possible that the AF being "faster" (as in, making decisions faster) can mean that it sometimes makes assumptions that are wrong. Or it may be that there is a straight up bug. OR it could just be user error - many times when people complained about AF on these forums it turned out that AF was just fine, but the user did not understand that a more contrasty background will attract focus more than their friend in a plain color sweater.
So, I would agree that in practice CD AF can be wrong, but out of completely different reasons than PD AF. Its not that the CD AF itself is wrong, its that the algorithms are not perfect. Also, I suspect that Pentax makes lens-specific CD AF algorithms. I suspect this because they often mention that a fw update has "improved CD AF for" certain new lens, like the new HD lenses.

I am surprised you mentioned the F 100 as having fast AF on the K-01, though! With my DFA 100mm, the K-01 is pretty slow and sometimes hunts in the wrong direction. But the lens has quickshift, so I try to adjust focus manually and only use AF to confirm. The K-01 is best with non-macro fast prime lenses.
12-15-2013, 02:51 PM - 1 Like   #4
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@Steve: CD-AF in theory can't be wrong. It adjust focus till gets the (absolute?, that's the point!) highest contrast. The algorithm decide when it is adequate high. When this "level" is set by a parameter in fw-software lower eg. for the sake of speed, the accuracy may suffer. For less sharp lenses or when DoF is high, no detectable problem. A sharp, esp. macro lens shows the effect.

@Horuk: you are right F100m AF is slooow (long focus drag, I didn't say it's fast, it's SHARP), sharper as non-macro, so I take the pain.
Belive me I try to sort out all other error sources incl. myself. I tried the fw stepdown when no other solution remained. And worked out.

My story is not a complain, finaly I find a fw (1.01) that suits my needs. Just a hint for K-01 user, who may have the same trouble.

12-16-2013, 08:39 AM   #5
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QuoteOriginally posted by Eduscho Quote
@Steve: CD-AF in theory can't be wrong.
It is correct that CD-AF can't be wrong ON CAMERA, in theory. But AF lenses keep wide open when camera focuses and meters, some lens might shift the focus as the aperture close down.
plus, I have a sigma lens back focuses quite a lot even on K-01. And more surprising: it does better on the yellow K-01 than on the white one! Both cameras are at same firmware version at that time!
There must be something more complicated than we think.
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