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This lens, a Nikkor 80-200 AIS, has some curved lines that are color coded to match the aperture ring. Originally I thought this was for focusing but playing around with it does not make it seem like that is.

Any idea what they might be indicating?

lens with color lines

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15

The aperture ring is engraved with f-numbers duplicated; the duplicates are color coded the same. The lines you are asking about are also paired, same color. The idea is to graphically display the zone of depth-of-field. As an example, you focus on an object at 10 meters (32 feet) as indicated by the thick center white line. Setting the aperture at f/8 (yellow), the span of the depth of field lies between the two yellow (color matching) lines.

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    "... the span of the depth of field for an 8x10 print enlarged from a 36x24 mm sensor/negative viewed at a distance of 12 inches by a person with 20/20 vision lies between the two yellow lines." – Michael C Aug 1 '18 at 7:48
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    It's irrespective of print size @MichaelClark, though print size would determine whether a detail would be visible with the naked eye if sharp on the negative. – jwenting Aug 1 '18 at 11:13
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    Depth of field with respect to a human observing a photograph is most certainly dependent upon print size. If you print two photos from the same negative, one at 16x20 and the other at 8x10 and set them side by side and view them both from the same distance it will be quite obvious to you. There's only one "sharpest" point of focus. How much blur on either side of that point is allowable before it can be perceived by a viewer is very much dependent on the enlargement ratio of the image. – Michael C Aug 1 '18 at 13:33
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    As a general rule of thumb, most depth-of-field tables, charts and lens engravings, yield satisfactory results when the resulting displayed image is viewed from a distance approximately equal to their corner to corner measure (diagonal measure). Basing the data on a circle of confusion of about 1/1000 of focal length usually takes viewing distance and the magnification used to make the display, into account. – Alan Marcus Aug 1 '18 at 13:42
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The unpaired red line is the infrared focal point, if you're using infrared film.

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