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10-04-2009, 07:48 AM   #1
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Calibrated Focus Screen

I purchased a split prism focusing screen from jinfiance on the bay about a year ago. I installed it and have been using it with my Vivitar 105mm macro and have been quite happy with it.

However I never found my 50mm 1.4 to be satisfactory, I knew it was "a soft lens" so I didn't expect too much. Until I was goofing around last weekend, and produced a sharp image. I was stunned...this is what my 1.4 can do, if not reliably.

Well Friday night I spent the better part of the night cutting sticky notes (light plastic 3M arrows) and discovered it took 4 of them stacked to get the BF issues resolved.

I have been thrilled and its opened up a new ability for me, and it made the Vivitar even sharper. And the 50mm 1.4 is very nice at 1.4.

So my advice to everyone who has one of these screens (or any other)...CALIBRATE IT

Otherwise you are not going to get the best out of it.

10-04-2009, 09:32 AM   #2
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QuoteOriginally posted by omega leader Quote
I purchased a split prism focusing screen from jinfiance on the bay about a year ago. I installed it and have been using it with my Vivitar 105mm macro and have been quite happy with it.

However I never found my 50mm 1.4 to be satisfactory, I knew it was "a soft lens" so I didn't expect too much. Until I was goofing around last weekend, and produced a sharp image. I was stunned...this is what my 1.4 can do, if not reliably.

Well Friday night I spent the better part of the night cutting sticky notes (light plastic 3M arrows) and discovered it took 4 of them stacked to get the BF issues resolved.

I have been thrilled and its opened up a new ability for me, and it made the Vivitar even sharper. And the 50mm 1.4 is very nice at 1.4.

So my advice to everyone who has one of these screens (or any other)...CALIBRATE IT

Otherwise you are not going to get the best out of it.
This is interesting. I have noticed front focusing for FA 31 and sigma 24 - 70 recently, and coincidentally I just changed my K20D genetic focusing screen to the LL-80.

Could I ask if the focusing affected was auto focusing?
10-04-2009, 09:38 AM   #3
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The focusing screen only affects manual focus. It does not affect auto focus.
10-04-2009, 10:45 AM   #4
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I always thought my bright (50/1.4 and 85/1.8) m42 lenses were back-focusing with my Katz Eye screen...after reading this thread I'm pretty sure it is. I have been strongly considering going back to my stock screen on the K10D, might just give it a try and see if I can get a few more keepers.

Thanks for the post.

10-04-2009, 12:24 PM   #5
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Pentax has metals shims of various thicknesses that are placed between the focus screen and the pentaprism optics. It's not obvious when you remove the focus screen -- I missed it the first time.

I had Katz calibrate and swap the shims for me:

https://www.pentaxforums.com/forums/pentax-dslr-discussion/35884-front-focusi...n-curable.html

In any case, you definitely need to check and possibly swap shims (at least on the K20D) if you are going to do any shallow DOF work. Your focus screen provider should be able to be able to provide a shim kit.

BTW, there's some debate as to whether this is caused by Pentax assembly tolerances or differing optical properties of various focus screens; I haven't seen convincing evidence to exclude either possibility.
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