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10-13-2012, 08:26 AM   #1
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Extra Red line on my A 28 2.8 ???

I have a Pentax-A 28mm f2.8

I understand the hyper focal relationship between the Red 10 foot distance and the Red f.8 but....

The first depth of field mark to the left of the scale is also RED.

What does this represent?

Thanks,
joe

10-13-2012, 08:45 AM   #2
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It's for IR focusing I believe.
10-13-2012, 09:05 AM   #3
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The mark above the orange diamond next to the 4? Yep, a mark to aid focusing when you're using an infrared filter.

10-13-2012, 09:10 AM   #4
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QuoteOriginally posted by blackcloudbrew Quote
It's for IR focusing I believe.
Ding! The prize goes to the brewster!

The IR mark is present on almost all the manual focus lenses I own. I have never used it, but I imagine the flow would be to establish focus through the viewfinder, apply the offset and shoot.


Steve

10-13-2012, 09:13 AM   #5
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QuoteOriginally posted by Just1MoreDave Quote
The mark above the orange diamond next to the 4? Yep, a mark to aid focusing when you're using an infrared filter.
Dave brings up the other good point that the viewfinder can be pretty dim when all the needed filters are in place. I have read of people composing (on tripod), focusing, adjust focus offset, and THEN put the filter on the lens! Long exposure times too.


Steve
10-13-2012, 12:19 PM   #6
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From Super-Program owners manual.

Last edited by Ex Finn.; 11-11-2014 at 05:46 PM.
10-13-2012, 01:49 PM   #7
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Original Poster
Hey, thanks every one. Nothing I will use but at least I understand the lens fully.

Thanks again,
joe
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