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08-10-2008, 02:08 PM   #1
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is my Program Plus focusing to infinity?

I recently shot a long shot, of the building that I work in. It was probably 200m away or more. I noticed that even with my lens turned all the way to infinity, the microprism on my Program Plus's focusing screen didn't go completely smooth. Close, but not quite. It was as if I wasn't able to focus far away enough to make the prism go smooth.

Now I can see two different possibilities

1. My lens doesn't focus all the way to infinity. Thus my microprism doesn't go away. Thus, all shots I take at infinity will be soft.

2. My focusing screen is out of adjustment, thus it shows microprism prismation even with the lens correctly focused at infinity. If this is true, my focus will be slightly off at all ranges, if I go by the microprism (or even if I go by eye?).

3. This is normal, and microprisms don't go smooth at infinity.

What do you think? Should I just ignore it?

Last edited by BetterSense; 08-10-2008 at 02:14 PM.
08-14-2008, 06:59 AM   #2
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How about the split-prism in the center, what did that indicate?

Also, what lens? Many newer (autofocus, in particular) lenses can actually focus beyond infinity.
08-14-2008, 07:09 AM   #3
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The microprism doesn't necessarily go all smooth with slower lenses - what aperture was the lens? Have you tried the same test with other lenses, to see if this is a constant thing or situational with just this one lens? And have you looked at the resulting photo? (I'd suggest taking two: one at infinity, and one just short of infinity so you can see the difference in the result, to judge the first photo better)

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