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04-10-2011, 03:31 PM   #16
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Another thought - maybe stray light entering lens throwing off the focus? Or, if you are using a filter, bounce between filter and lens?

I went out once in broad daylight with my A50 and got a series of out of focused pictures. Very depressing. After some investigation, I discovered it was bounce between my el cheapo non multi coated filter and the lens. As soon as I took the filter off, everything was in "focus" (in reality, lack of softness caused by bounce).

04-10-2011, 03:33 PM - 1 Like   #17
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QuoteOriginally posted by JohnBee Quote
And so I began doing some AF testing this week with my K-5 and I discovered something rather interesting. Which isn't particularly inherent to the K-5(per say), but... seems far more prevalent on the K-5 and so I thought I'd write about it here.

So here's the thing... Is anyone else under the impression that AF confirm was a completely separate thing from the AF module? For example.... when the AF confirm indicator is lit(hexagonal indicator in VF), then the camera is in focus right?

However... a few days ago, I realized that using the AF indicator with a MF lens proved to be off. Way off in fact... However... when I put an AF lens on the camera(same aperture and settings) focus was spot on! - How can this be(I thought), as I tied another MF lens for added testing. Same thing!

And so I'm now wondering if the focusing screen might not have something to do with AF confirm in MF mode? Or am I completely confused in my way of thinking?

Anyways, for what it's worth, the K-5 has a substantial FF issue when using AF confirm and a MF lens whereas the K20D does not.

Any suggestions?
This is probably the reason:
Manual Focus with AF DSLRs

/Lage
04-10-2011, 07:07 PM   #18
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QuoteOriginally posted by Lage Quote
This is probably the reason:
Manual Focus with AF DSLRs

/Lage

While modern focus screens in dales make it more difficult to ensure accurate focus with your eyes, it won't have any impact on AF confiramtion, which does not rely on light coming through the focus screen.
04-10-2011, 07:42 PM   #19
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QuoteOriginally posted by JohnBee Quote
I just thought of a new test that I think might shed a little more light on this.

I'm going to try after lunch and see if the issue appears on an AF lens in MF mode.
If so... then I guess there isn't much else that could be done.
Though something tells me that the issue if likely not so much a mechanical one as something that should be address with FW.

I've already contacted Pentax about the issue, but I doubt they will respond before my return period ends(Wednesday). Luckily, my camera dealer is very lenient with returns and so I'll likely get an extension to help figure this out first.

Either way, I'll post my results here shortly.
+1 on the test. I think the focus screen needs adjustment, there are shims. If so, manual focus photos with AF lens will be front focus too.

04-10-2011, 07:54 PM   #20
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It's pretty much been determined at this point that the K5 will suffer from AF failure in some situations (low light that is predominantly reddish). Low tungsten light and candle light are good examples of what will cause the K5 to fail.
The focus indicator is tied directly to the AF module, so in situations where the AF would fail, the indicator is going to give an incorrect focus indication when manual focus is being used.
My advice is trust your eyes.
04-10-2011, 09:08 PM   #21
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QuoteOriginally posted by JohnBee Quote

So here's the thing... Is anyone else under the impression that AF confirm was a completely separate thing from the AF module?
Not at all. the AF confirm for MF lenses si simply the phase AF system without the mechanism to autofocus the lens.


QuoteQuote:
For example.... when the AF confirm indicator is lit(hexagonal indicator in VF), then the camera is in focus right?
not if it's not calibrated correctly.

QuoteQuote:
Anyways, for what it's worth, the K-5 has a substantial FF issue when using AF confirm and a MF lens whereas the K20D does not.

Any suggestions?
Yes. Calibrate your MF lens with the AF adjustment and remember the setting. When attachign that particular lens dial in the AF setting.

the K20D is not immune from this. I had to do this for some MF lenses on my K20D
04-10-2011, 09:12 PM   #22
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QuoteOriginally posted by Wheatfield Quote
It's pretty much been determined at this point that the K5 will suffer from AF failure in some situations (low light that is predominantly reddish). Low tungsten light and candle light are good examples of what will cause the K5 to fail.
The focus indicator is tied directly to the AF module, so in situations where the AF would fail, the indicator is going to give an incorrect focus indication when manual focus is being used.
My advice is trust your eyes.
You've obviously never used lenses with wide apertures like F/1.4 and F/1.2 etc

A focus(viewfinder) screen can't see such shallow DOFs. i.e what your seeing on the screen is a DOF that you'd get from an aperture around F2.8 when the aperture is in fact f/1.2.

try it. Borrow an F/1.2 or F/1.4 lens and take a picture. There's a huge difference between the DOF you see in the viewfinder and on the picture itself.
04-10-2011, 09:48 PM   #23
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QuoteOriginally posted by Smeggypants Quote
Calibrate your MF lens with the AF adjustment and remember the setting. When attachign that particular lens dial in the AF setting.
This has me confused. A manual focus lens, such as the SMC-M 50/1.7, does not have a chip inside, that identifies the lens to the camera. Why would I have to enter the focal length to begin with. I can see how a "global" adjustment to the sensor can help, but not for individual MF lenses.

Edit :
Sorry, I re-read your post and now I get it. You use the AF fine adjustment as a reference, but reset the adjustment back to zero. When re-mounting the lens you now have a "known" AF adjustment setting..., a bit cumbersome, but workable.


Last edited by Catalana; 04-10-2011 at 09:54 PM.
04-10-2011, 11:48 PM   #24
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The greatest difference between AF and MF lenses is their focus throw. AF lens has very short and MF lens has very long focus throw. So, when an MF lens is used, the window for "focus confirmation" is wider, therefore less accurate or very inconsistent. To compensate for this, stop down your lens aperture. Also, depending on which spot of the focus throw you start focusing with, from MFD or from infinity, sometimes the focus confirmation may differ in accuracy also. My conclusion is to know each MF lens intimately and dial in the correct AF fine tuning before you shoot with that particular lens.
04-11-2011, 12:13 AM   #25
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I don't know, but I assumed that AF adjustment for manual lenses would be tied to the entered focal length. So as long as you don't use multiple MF lenses with the same focal length it would work just fine.
04-11-2011, 12:24 AM   #26
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I do find it odd, I recently aquired a bunch of SMC tak's and a Tamron Adaptol lens, Using catch in focus for the Tamron reqiures the focus confirmation.. but for normal manual shooting I just eye-ball it. I don't like the viewfinder focusing screen, so I'm going to pick up a Katz-eye one soon.
But I turned on the AF confirmation red box in the viewfinder, I use center AF point, so when I'm shooting with manual lenses I get the beep and red box.. but then I still need to tweak the focus a bit more to get IN focus.
04-11-2011, 01:31 AM   #27
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Kyllä kaikki Pentax linssit pelaa oikein, minun K-5, kun käytän DA* linssejä. Toimii AF ja MF niinkuin pitääkin. Jopa Sigma 100-300 F4 1.4x - 2x lisäkken kanssa. Enpä kyllä etsikkään vikoja vaan lopputulos ratkaisee. Olenpa ottanut muutamia ***** kuvaakin.
04-11-2011, 03:04 AM   #28
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QuoteOriginally posted by Smeggypants Quote
not if it's not calibrated correctly.
Wouldn't the fact than an AF lens be spot on, go to show the AF is calibrated?

QuoteQuote:
Yes. Calibrate your MF lens with the AF adjustment and remember the setting. When attachign that particular lens dial in the AF setting.

the K20D is not immune from this. I had to do this for some MF lenses on my K20D
I don't know if I'm the only one who's seen this, but the calibration module seems to be disabled when MF lenses are attached to the camera. As far as I know, the lens calibration module requires that the lens be identified in order to work. And though I can't say for sure, I think this may go for global adjustments as well.
04-11-2011, 06:58 AM   #29
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QuoteOriginally posted by JohnBee Quote
Wouldn't the fact than an AF lens be spot on, go to show the AF is calibrated?
The wonders of consumer-level production tolerances and quality control mean that it is not possible to have one AF calibration for all lenses.

That's why Pentax cameras allow individual AF adjustments for individual lenses.

If all your MF lenses FF (via the AF confirmation) by roughly the same amount, it could mean that your camera needs an overall adjustment (but you then you should observe an overall bias required for individual AF adjustments).

Have you ruled out the influence of low-light / yellowish light? AF confirmation on the K-5 will suffer from the same FF issues that plague its AF performance. I recommend bright daylight for your tests.

Note that the AF confirmation window is a bit large. Try to approach the point of making the AF hexagon light up from both infinity and MFD. You should see a slight difference in where the focus ends up.

I use AF confirmation for MF lenses on my K100D all the time and it works like a charm. Maybe some practice helped, I think I'm better now at hitting the mid-point of the range when the hexagon lights up.
04-11-2011, 08:30 AM   #30
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QuoteOriginally posted by Chex Quote
the viewfinder, I use center AF point, so when I'm shooting with manual lenses I get the beep and red box.. but then I still need to tweak the focus a bit more to get IN focus.
My K-5 was the same. After I installed the Katz-Eye, it was *still* the same. Furthermore, with the Katz-Eye installed, I could focus very precisely and discover that the image was front focussed. Turns out I needed a different shim; I removed the factory .40 and replaced it with a .1 + .15 (couldn't find a .25 shim; Rachel Katz was tremendously helpful in this process). Initially I tried a .20, and it was very inconsistent; Finally, I took it out and looked at it with a magnifying glass and discovered a tiny kink on one edge that caused the screen to sit at an angle. Now, with the proper shims, I get solid, accurate manual focus.

1.03 fixed most of my autofocus problems. I say "most" because I still get an occasional flyer that doesn't make any sense. I don't often use AF in low light anyway; my K20D wasn't accurate enough with the 50 1.4 or 35 f2 wide open, so I used a Katz-Eye and focused manually. The K-5 is so much faster in good light (at autofocus) it's still a major step up.

Last edited by jstevewhite; 04-11-2011 at 08:32 AM. Reason: clarity
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