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12-20-2009, 08:42 PM   #1
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SMC-A 70-210 lens markings?

I just got this lens last week, but I've searched high and low to try to make sense of the lens markings. In the attached photo of this lens, the lens is set at 85mm and I understand that the red diamond and the line above it points to the focal distance, or the distance from camera to subject. In this case, I've set the subject 15 feet or about 4.5 meters away. I also realize that if the aperture is set to f/8, I follow the white curved lines above the "8" on either side of the red diamond and find that the depth of field or "range of acceptable focus" of the image will extend from 9 to 50 ft. (or ~2.7 to 15 m) in front of the lens. Is this all correct so far?

But now my confusion: What do the four curved lines between the two outer curved lines represent? Are the two lines on either side of the center red line representing the depth of field when at f/4 and the two lines beyond this (and between the f/8 lines) the lines representing f/5.6? Also, why are two of the lines red?

I look forward to manual lens experts clarifying all this for me!

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12-20-2009, 09:38 PM   #2
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Those curved lines are the indicators for depth of field. They are curved to account for the different focal lengths. With this lens, pulling increases the focal length and the depth of field narrows. Take them as meaning that a 35mm negative can be printed at 8x10 inches and appear in focus from a 10 inch viewing distance at the distances indicated against the f/stop markings on the focus scale.

The inner lines are f/5.6 and f/4 depth of field scales.
12-20-2009, 11:20 PM   #3
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Okay, here's another question. After trying to make sense of various web sites to try to determine hyperfocal distance with a lens like this, if I put the infinity symbol on the left-most line of f/8 - and assuming an 85mm focal length once again - that will make my focal point 20 ft. (6m) and my depth of field from 10 ft (~3.2 m) to infinity, according to the depth of field scale on the lens. Is this how I determine the hyperfocal distance, and is this 20 ft. (6 m) the hyperfocal distance?

I understand what hyperfocal distance is and what it means, I just need to know if this is how I determine it with this lens.
12-21-2009, 11:41 AM   #4
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QuoteOriginally posted by enoxatnep Quote
Okay, here's another question. After trying to make sense of various web sites to try to determine hyperfocal distance with a lens like this, if I put the infinity symbol on the left-most line of f/8 - and assuming an 85mm focal length once again - that will make my focal point 20 ft. (6m) and my depth of field from 10 ft (~3.2 m) to infinity, according to the depth of field scale on the lens. Is this how I determine the hyperfocal distance, and is this 20 ft. (6 m) the hyperfocal distance?

I understand what hyperfocal distance is and what it means, I just need to know if this is how I determine it with this lens.
Absolutely correct.

12-21-2009, 04:12 PM   #5
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I never used this lens for IR but was under the impression that the red lines were used for IR focusing, correct me if I am wrong.

Cheers from the frozen south, Mike.
12-21-2009, 04:20 PM   #6
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QuoteOriginally posted by Ex Finn. Quote
I never used this lens for IR but was under the impression that the red lines were used for IR focusing, correct me if I am wrong.

Cheers from the frozen south, Mike.
Correct; The straight red line is the mean focus distance and the curved one is the IR focus distance. The depth of field lines obviously only applies to 'standard' light
12-22-2009, 04:02 AM   #7
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Thank`s and happy holidays.
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