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05-09-2009, 07:12 AM   #1
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Katz Eye vs K20D AF Adjustment ??

I have a DA lens that needs & has been set +3 AF adjustment on my K20D. If I install Katz Eye (with assumption the Katz Eye introduces no accuracy error of its own), and intend to use AF then quickshift to line up the split image, should I reset the AF adjustment for this lens back to zero first?

Thanks in advance for your help.

05-09-2009, 08:45 AM   #2
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QuoteOriginally posted by Kguru Quote
I have a DA lens that needs & has been set +3 AF adjustment on my K20D. If I install Katz Eye (with assumption the Katz Eye introduces no accuracy error of its own), and intend to use AF then quickshift to line up the split image, should I reset the AF adjustment for this lens back to zero first?

Thanks in advance for your help.
The AF bias is there to garner accuracy between AF and manual focus (presuming your screen is accurate).
If manual focus is giving you accurate focus, you should
ensure the AF is biased so that it matches manual focus.
If your manual focus is not giving you accurate focus, you need to have your camera fixed.
05-09-2009, 04:12 PM   #3
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Focusing screen does not affect auto focus in any way. Therefore if you was happy with your AF +3 adjustment - leave it like that.

Focusing screen affects manual focus though. It appears that not all K20D and Katz Eye combinations works OK without calibration. Thereforeafter fitting Katz Eye screen you must check if your manual focus is 100% OK.

Calibrating manual focus is an easy thing to do, you just need to get calibration shims from CR Kennedy. They are cheap, $3 each. Front focus fixing needs thinner shims, back focus fixing needs thicker shims.

Calibrationg focusing screen may sound like a difficult thing for DIY, bit it isn't. It took me less than a minute to replace focusing screen calibration shim. Of course, precision tweezer is a must.
05-10-2009, 09:41 AM   #4
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Thanks Wheatfield & Edvinas for your advice. Let me report my experience in case it is of help to someone.

I installed not the Katz Eye but the Shanghai version from ebay, much cheaper at US$22 incl shipping to Aust. Many have warned about scratches and dust, thankfully I found installation not so scary. I was quite nervous on the 1st pass, but when I found a few bits of dust I was confident enough to take it out blow off and reinstall all in 3 minutes. All clean now

My lenses that didn't need AF adjustment still don't. The ones that did need some have to be redone, so it's academic to ask whether to leave AF adjustment as was or reset to zero.

Most interesting is I've found with this focus screen my K20D's AF is SIGNIFICANTLY more accurate in terms of focusing on the spot I want it to focus. It feels almost like spot focus that I've wanted all along.

On manual focus it suffers a tiny bit of misalignment i.e. shooting AF is spot on but if I use quickshift to line up perfectly the split image then the pic comes out with slight front-focus. I didn't see any shim in there so can't use a thinner shim to negate this front-focus. Any advice please?

Only negative comment is I wish Pentax had designed the holding frame with positive-feel "guides" where the screen is to sit in. As it is the screen seemed to sit loose on the frame, nothing to instill confidence that it was in its proper position before I latched the frame back.

Cheers


Last edited by Kguru; 05-10-2009 at 10:02 AM.
05-10-2009, 04:53 PM   #5
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QuoteOriginally posted by Kguru Quote
Most interesting is I've found with this focus screen my K20D's AF is SIGNIFICANTLY more accurate in terms of focusing on the spot I want it to focus. It feels almost like spot focus that I've wanted all along.
That's placebo

AF sensors are on the bottom of the mirror box, light going to AF sensors does not pass through focusing screen therefore focusing screen can't make any influence to AF. Take out focusing screen and you will see that camera fill successfully autofocus without it

QuoteOriginally posted by Kguru Quote
On manual focus it suffers a tiny bit of misalignment i.e. shooting AF is spot on but if I use quickshift to line up perfectly the split image then the pic comes out with slight front-focus. I didn't see any shim in there so can't use a thinner shim to negate this front-focus. Any advice please?
Request calibration shims from Pentax. CR Kennedy in Melbourne were extremely helpful, hope they will be the same in Perth

Here are part numbers:
76830.M02200A - 0.15mm
76830.M02200B - 0.20mm
76830.M02200C - 0.25mm
76830.M02200D - 0.30mm
76830.M02200E - 0.35mm
76830.M02200F - 0.40mm
05-10-2009, 07:00 PM   #6
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QuoteOriginally posted by Edvinas Quote
That's placebo

AF sensors are on the bottom of the mirror box, light going to AF sensors does not pass through focusing screen therefore focusing screen can't make any influence to AF. Take out focusing screen and you will see that camera fill successfully autofocus without it
Is that so?
I had thought about that too. I guess with the original screen I would not have noticed when it happened to focus on an adjacent spot, only knowing about it after the fact (and I had quite a few). With the new screen it's apparent rightaway so the finger instintively stops from pressing all the way. Anyway net effect was I did not have a single AF mis-focused shot out of 200+ test shots.

Back to the shim issue, if it presently doesn't use any shim how can I calibrate with thinner ones?
05-10-2009, 09:27 PM   #7
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QuoteOriginally posted by Kguru Quote
Back to the shim issue, if it presently doesn't use any shim how can I calibrate with thinner ones?
Well, in this case you're in trouble

However I doubt that your camera is without focusing screen calibration shims.
Usually K20D have 0.35mm shim fitted in factory.
05-10-2009, 09:47 PM   #8
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QuoteOriginally posted by Edvinas Quote
Well, in this case you're in trouble

However I doubt that your camera is without focusing screen calibration shims.
Usually K20D have 0.35mm shim fitted in factory.
Ok to be absolutely sure:
- when I release the holding frame and lower it toward the mirror, is the shim under or on top of the focus screen?
- is it obviously there to be seen or do I have to "look" for it?

I didn't see one, could it be sticking to the upper part inside camera where the holding frame swung down from?!!!!

05-11-2009, 04:46 AM   #9
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Calibration shim is between focusing screen and pentaprism. It becomes visible when you take out focusing screen.

Here's how it looks:


Together with SD card to get a feeling of it's size.:


For obvious reasons I was not able to take a picture of a shim fitted in it's place.
05-11-2009, 09:29 AM   #10
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If I'm looking at the focus screen from the lens side wich side does the shim go on? The side you see or the back side.. Mine came out installing the Katzeye screen and I went back to the old screen and need to put it back in.

Thanks
Jack
05-11-2009, 05:16 PM   #11
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QuoteOriginally posted by Fl_Gulfer Quote
If I'm looking at the focus screen from the lens side wich side does the shim go on? The side you see or the back side..
Calibration shim must be on the back side.
06-24-2009, 11:32 AM   #12
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Sounds linke I need a thinner shim as my current one... trouble is, it's quite hard to get them from shops in France (they don't have spare parts).

I could use sandpaper on it, but considering (voidance of) warranty I'd prefer to use this on a spare one.
So, if someone has unused shims, and could ship them to France in a letter, please do contact me... I have no clue how much this costs, though. And a partial set of different thicknesses would interest me even more.
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