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05-09-2009, 03:01 AM   #1
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Why is F16 marked in blue? What is the red 'R'?

1. On the Vivitar 105mm F2.5 F16 is marked in blue. Why is this? Is it telling me the the lens is sharpest there, or that above this is the point (f22 etc) you start losing sharpness?

2. On two other lenses, there is a red R with a line extending along the barrel? What is the red R?


05-09-2009, 03:15 AM   #2
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The R may be an infrared focus mark, older manual focus lenses I've owned have an offset, red focus mark for when using infrared film. Nikon used to have different colours on the depth of field scales on their lenses.
05-09-2009, 04:50 AM   #3
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Makes sense

Thanks for the answer to Q 2.


05-09-2009, 04:50 AM   #4
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On my Vivitar f16 is in blue and f32 is in green. These correspond to the blue and green lines on the depth of field indicators. Given that this is a macro lens and that smaller apertures are more often used, I think it's just an ease of use colour coding. And yes the red R is an infrared mark. Back in the manual focus 35mm days the ritual was to focus the lens and then align the distance with the red R. I believe this is because lenses focus the infrared rays behind the focal plane. When I shot IR film, I was lazy and would just use an aperture that would ensure enough depth of field to contain the R on the focus scale.

05-09-2009, 11:35 AM   #5
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As note, hyperfocal ranges were often color-coded between the range scale and the aperture ring.

On a slightly different topic, there are also some interchangeable mount lenses that have more than one, color-coded aperture scale to accommodate the mechanical differences in the various moiunts - the Vivitar 400/5.6 TX-mount is a common example.

05-09-2009, 09:45 PM   #6
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thanks for the replies

I think you're right, it is an ease-of-use thing, it also has the F32 in green.

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