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06-12-2008, 05:51 AM   #1
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Close-up lens markings

I have 4 Asahi Pentax closeup lenses marked T80, T160, S25 and S40.
I dont understand what those marks mean - what diopter are these?

06-12-2008, 06:17 AM   #2
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QuoteOriginally posted by gamgee Quote
I have 4 Asahi Pentax closeup lenses marked T80, T160, S25 and S40.
I dont understand what those marks mean - what diopter are these?
I have a book called "the PENTAX Guide" Published just after the release of the M series lenses.

In this bookthere is a table

the following is provided for your lenses.
- S25 maximum focus distance on 50mm lens 12.71 inch, which I would interperate as 3 diopters
- S40 maximum focus distance on 50mm lens 18.72 inch, which I would interperate as 2 diopters
- T80 maximum focus distance on 50mm lens 35.72 inch, which I would interperate as 1 diopter
- T160 maximum focus distance on 50mm lens 68.25 inch, which I would interperate as 0.57 diopters

I have made this assessment on the basic point that the maximum focusing distance of any lens with a close up attached is 1/diopter in meters. a 1 diopter close up has maximum focus of 1 meter, 2 dippter is .5 meters etc. based upon the fopcusing distances given, and some liberal rounding off, the above is very close.
06-12-2008, 06:28 AM   #3
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Thank you Lowell
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