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04-03-2013, 01:00 AM   #1
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Red marks -- 10 3 ???

My old Pentax-A f/2.8 28mm lens has a red '10' and '3' next to the infinity mark on the distance scale. For feet and meters. Got that. But why are these numbers in red, not blue and yellow like the other distance numbers?

And, if I line up the red 10-and-3 with the red diamond on the fixed aperture scale... what does that mean? See pic below. Is it a quick way to get hyperfocal... for everything? Or, does it mean something else?

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04-03-2013, 01:32 AM   #2
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Cheap Chinese UV filter ruining all that PENTAX optical goodness! Shame on you Jon, shame!..

Is this the same lens?
SMC Pentax-A 28mm f/2.8
SMC Pentax-M 28mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database
04-03-2013, 01:33 AM   #3
hcc
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I do not know for the red 10 and 3, but the 'red diamond' is in fact with a 'red arrow' with line up wit the Green A when you set the lens to Automatic Aperture (A).

Hope that the comment may help.
04-03-2013, 01:54 AM   #4
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@Sledger -- I want to have a clear filter over the lens, because I carry the camera around without a lens cap. Recommendations? And yes, it's the same one as on Ken Rockwell... an A-type... apparently the same as an M but with the A setting.

@hcc -- thanks... yes, the red arrow it does line up with the green A, as in the photo above. I keep the lens on A all the time. But I'm curious about the red '10 and 3'. Why would Pentax mark these numbers in red?

04-03-2013, 02:22 AM   #5
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The smallest red mark is used for shifting focus when shooting infrared. The red diamond is the focus point. The 10 and 3 as well as f8 are red because thats the implied best setting that will make everything from 5 feet to infinity in focus. Hope that helps!

and I would consider buying a metal lens hood in place of the cheap filter.

Last edited by Chris Stearns; 04-03-2013 at 02:28 AM.
04-03-2013, 04:30 AM   #6
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QuoteOriginally posted by jon404 Quote
@Sledger -- I want to have a clear filter over the lens, because I carry the camera around without a lens cap. Recommendations?
Like Chris, I suggest a lens hood.
04-03-2013, 05:39 AM - 1 Like   #7
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The red/orange "10 3" are the hyperfocal distance for f/8 (also orange). A lot of the Pentax wider primes have the f/8 hyperfocal distance marked this way, going back to the Takumars. The orange line just to the left of the diamond is the infrared focusing mark. Since the hyperfocal distance was calculated for 35mm, for APS-C some people go one f-stop higher; I like to crank the lens a little to the right. That makes everything from 7 feet to infinity "acceptably sharp".



Last edited by THoog; 04-03-2013 at 05:55 AM.
04-03-2013, 04:20 PM   #8
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Thanks all -- will check out metal lens hoods, and -- Thoog -- what a perfect explanation. You know, if I was a reporter with an APS-C Pentax, I might just leave it on 10-3 f/8 (or f/11) for anything reasonably close, and at infinity for far away. Or at your setting for whatever comes along!

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