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09-09-2008, 10:09 AM   #1
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K20D AF adjustments

I've been toying with this new features since a few days (I got my K20D 2 weeks ago). I tried to use focus charts at 45° but I've been frustrated by the inconsistant results.
I've tried this:
- Nikon D70 Focus Chart
- The special chart by Yvon Bourque
- Jeffrey Friedl’s Blog Jeffrey’s Autofocus Test Chart
- AF microadjustment for the 1Ds mark III and 1D Mk3
- ISO 12233 Test Chart

The last one I liked best. I don't think I like angled test charts that are not always easy to interpret correctly at least on the LCD screen. With the parallel to the focus plane charts, I can do tests shots and compare them at high magnification quickly.

My adjustments so far:
- FA50/1.4: -10 ! Now I will not say that this lens is very soft wide open. It's still not tack sharp but it's hugely better now.
- DA40/2.8: -4
- FA77/1.8: -5

The zooms were mostly correct and didn't seem to need adjustments. But they also are usually much darker and thus maybe their DOF mask any AF inacuracies.

Now I wish it would be much easier to correct the lenses. Not easy to see the difference between -1 and -2 for example. A fool proof method that Pentax could offer is:
- let us download and print a test chart (or include it in the box)
- AF the chart, then manually focus the chart (with a better liveview, it would be easy)
- The camera would then compute the difference and set the adjustment number automatically

Also, I think +/- 10 is maybe not enough. Other camera makers offer +/- 20 adjustments. The "Apply to All" should be cumulative and should be seen as correcting a body misalignment.

At least this feature improves the performance of some lenses, especially the wide aperture primes.

Here is the FA50 examples shot at f/1.4:
Unadjusted:


Adjusted:


09-09-2008, 11:51 AM   #2
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How did you do this and can this also be done with K10D ? What equipment do I need?
09-09-2008, 11:56 AM   #3
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QuoteOriginally posted by ManuH Quote
My adjustments so far:
- FA50/1.4: -10 ! Now I will not say that this lens is very soft wide open. It's still not tack sharp but it's hugely better now.
- DA40/2.8: -4
- FA77/1.8: -5
if you have only Pentax lenses it might be better to send K20D and lenses to Pentax... unfortunately it is not doable w/ non Pentax lenses.
09-09-2008, 11:58 AM   #4
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QuoteOriginally posted by per Quote
How did you do this and can this also be done with K10D ? What equipment do I need?
roll back to old ROM, change, roll forward to whatever latest ROM you need (or keep it old if you do not need the latest features) or get software written by one user using stolen .DLL from Pentax service center...

09-09-2008, 12:46 PM   #5
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It's a little more complicated for K10D. Not only do you need to have an older (outdated) firmware (v1.1 would probably be OK), it is hidden in a diagnostics screen that you need to press a certain button combo to see. Even then, you only get one global adjustment for all lenses--no per-lens settings.
09-09-2008, 12:58 PM   #6
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Another test, that should be even better and simpler:
TKP BLOG Blog Archive Testing the D300 AF FineTune Feature

In short, use dollar (or whatever your currency) bills. They have very fine details that should reveal any slight misfocus.
09-10-2008, 10:26 AM   #7
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I was reading penta-club.ru and the topic there ( Гуляние автофокуса в К20Д - Форумы Пента-клуба ) reminded me that
solution probably exists... not cheap one - but...

B+W #486 filters ... they cut UV __AND__ IR !!! but they cost a lot... like ~$170 (or so) for 72mm... or ~$140 (or so) for 49mm... but then your
tungsten IR spectrum will be almost eliminated...
09-10-2008, 12:50 PM   #8
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Manu, I feel your pain.

The only wide-aperture AF lens I have is the FA 50, but I too need to set my K20D at -9 or -10 to get satisfactory results when using indoor artificial lighting. Outdoors in sunlight, it's pretty much fine at zero. Can you test again in natural light, or confirm the conditions under which you performed your first tests?

But I DON'T necessarily think this is an infrared problem, because I get the same results (fairly severe front-focusing) with fluorescent lights in tinted glass fixtures. In my living room I have stained-glass lamps with compact fluorescent bulbs, and the lamps cast a decidedly warm-yellow tone. The infrared content is probably minimal. See, e.g.:

http://www.colorpro.com/info/images/fluores.gif

The spectral content of fluorescent bulbs diminishes to nearly zero at 700nm and greater, which is where infrared begins. And the stained glass itself should only subtract from the spectrum, not add.

But I still need to compensate -9 or -10 to get the FA 50 to work at anything f/2.8 or bigger.

09-10-2008, 01:03 PM   #9
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QuoteOriginally posted by Quicksand Quote
And the stained glass itself should only subtract from the spectrum, not add.
man, by doing that it heats -> emits IR... or where do you think all that missing spectrum goes ?
09-10-2008, 04:28 PM   #10
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QuoteOriginally posted by deejjjaaaa Quote
man, by doing that it heats -> emits IR... or where do you think all that missing spectrum goes ?
Um, I understand what you're saying . . . but the lamps aren't that hot!

By Wien's Displacement Law, that stained glass lampshade at about 25 degrees celsius emits most strongly at 2.9e+6 / (25 + 273) = 9700nm, which is waaaaay into long-wavelenth infrared, and is emitting the same wavelengths (more or less) as everything else in the room, including whatever I'm trying to focus on, regardless of lighting conditions.

Not only is that IR emitted from the lamp unlikely to confuse the sensor, but its amplitude is waaaaay below that of the ambient/reflected visible light, right?

That's not necessarily so with incandescent lighting, where the lamp actually DOES make a lot of near-infrared energy too, and that's reflected around just like the visible light.

Last edited by Quicksand; 09-10-2008 at 04:33 PM.
09-10-2008, 07:28 PM   #11
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QuoteOriginally posted by Quicksand Quote
Um, I understand what you're saying . . . but the lamps aren't that hot!

By Wien's Displacement Law, that stained glass lampshade at about 25 degrees celsius emits most strongly at 2.9e+6 / (25 + 273) = 9700nm, which is waaaaay into long-wavelenth infrared
Wien's displacement law - Wikipedia, the free encyclopedia

it is just the peak and @ 300 kelvin you are getting pretty shallow graph... compare w/ the sun @ 5500 kelvin
09-10-2008, 07:35 PM   #12
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QuoteOriginally posted by Quicksand Quote
but its amplitude is waaaaay below that of the ambient/reflected visible light, right?
how about the area under the graph ?
09-11-2008, 07:17 AM   #13
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So this can definitely not be done for my Sigma's glass on my k20d then?
09-11-2008, 01:18 PM   #14
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I'll put up my area-under-the-visible-light-spectrum against your area-under-the-long-wavelength-IR-spectrum any day of the week!



I don't know the answer here. And really, I'm not trying to dismiss the idea that IR leads to poor focusing performance. It might very well be a contributor. But I'm just asserting that I think there's more to it than that. I'd love it if my K20D would focus in the dark based on ambient thermal IR, even if it were off a little, but it doesn't!

I continue to think that my filtered-fluorescent scenario is evidence pointing to other factors, since there's very little IR being emitted from those lamps. Not zero, but little. But the color cast is similar to that of tungsten incandescent lighting, and I get similar focusing performance.

I'd love to test my hypothesis, but I'm not gonna lay out the cash for an IR spectrometer or those expensive B+W filters, not while there are all those nice used MF lenses calling my name on eBay!
09-11-2008, 02:47 PM   #15
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QuoteOriginally posted by Quicksand Quote
I'll put up my area-under-the-visible-light-spectrum against your area-under-the-long-wavelength-IR-spectrum any day of the week!


go Calculus... let integrals shine in their full glory.


QuoteOriginally posted by Quicksand Quote
I don't know the answer here. And really, I'm not trying to dismiss the idea that IR leads to poor focusing performance. It might very well be a contributor. But I'm just asserting that I think there's more to it than that.
right, but what else ? if one spectrum leads to 100% precise AF and another spectrum leads to the error on the same equipment that means
the key is what hits the AF sensor in both cases... now if we can find somebody w/ 486 series filter from B+W we can easily test the IR theory or else is that good APO (Apochromat - Wikipedia, the free encyclopedia) glass should be less affected by BF/FF by design...




QuoteOriginally posted by Quicksand Quote
I'd love it if my K20D would focus in the dark based on ambient thermal IR, even if it were off a little, but it doesn't!
I am not sure we are dealing w/ just ambient thermal IR...

QuoteOriginally posted by Quicksand Quote
I continue to think that my filtered-fluorescent scenario is evidence pointing to other factors, since there's very little IR being emitted from those lamps. Not zero, but little.
how do you know that it is that little if a lot of it of the lamp is absorbed by your tiffany glass shade ?...


QuoteOriginally posted by Quicksand Quote

I'd love to test my hypothesis, but I'm not gonna lay out the cash for an IR spectrometer or those expensive B+W filters, not while there are all those nice used MF lenses calling my name on eBay!
we just need to find somebody w/ that expensive filter...

Last edited by deejjjaaaa; 09-11-2008 at 02:52 PM.
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