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02-25-2012, 08:22 AM   #16
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I'll second Adam - I've also read somewhere that it is mark for infrared photography

02-25-2012, 08:54 AM   #17
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The red f8 and the red 3 meter distance mark are "fixed-focus" marks for shooting snapshots. If you align the f8 to 3 meters you do not have to focus and everything from 1.5 meters to infinity will be in focus. Notice the infinity and 1.5 meter mark lines up over the f8 mark on the scale. I use the scales all the time as I only use MF.

Phil
02-25-2012, 10:48 AM   #18
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Also, for the IR claims, that is also true as the old pentax manuals when referencing IR photography note to line up the "IR Marks" - this was referred to as blind focusing as when an IR filter is attached you can't see through (well, very little but impossible to focus through the VF with the filter on) the lens.
02-25-2012, 11:04 AM   #19
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QuoteOriginally posted by joe.penn Quote

Also, for the IR claims, that is also true as the old pentax manuals when referencing IR photography note to line up the "IR Marks" - this was referred to as blind focusing as when an IR filter is attached you can't see through (well, very little but impossible to focus through the VF with the filter on) the lens.
On the K28/3.5 picture the IR index mark is the orange line above f4 to the left of the "diamond". If you were shooting IR film with an IR filter and your subject distance was infinity, you would move the infinity mark from the orange "diamond" mark to the IR index mark above the left "4" to compensate for focus shift.

Phil.

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02-25-2012, 12:58 PM   #20
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QuoteOriginally posted by gofour3 Quote
On the K28/3.5 picture the IR index mark is the orange line above f4 to the left of the "diamond". If you were shooting IR film with an IR filter and your subject distance was infinity, you would move the infinity mark from the orange "diamond" mark to the IR index mark above the left "4" to compensate for focus shift.

Phil.
Very helpful
02-26-2012, 11:22 PM   #21
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As the attached photos show, these marks weren't just limited to the wide angles. Here they are on a telephoto (Takumar (Bayonet) 135mm f/2.5).

There are three sets of colored f-stops (blue f/4. orange f/8, yellow f/16) and corresponding colored focus distance marks.

Notice also the red dot below the left side focus mark for f/11. Perhaps that is for IR?
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