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+  The Canon EOS and Photography Forums
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| |-+  Technical Questions on Photography and Optics
| | |-+  Lines per mm. in relation to magnification factors.
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Author Topic: Lines per mm. in relation to magnification factors.  (Read 7254 times)  bookmark this topic!
Posts: 2

Lines per mm. in relation to magnification factors.
« on: January 04, 2009, 07:45:07 AM »

I have downloaded pages from and would like to know the following:-

When comparing lpm from the tables illustrated, how critical is the difference between.... RESOLUTION at xxmm at 1:48 magnification
                                                                                                               and... RESOLUTION at xxmm at 1:50 magnification?

I appreciate that what makes a 'good' lens is not always its resolving power and that there are other considerations but my curiosity
is aroused by the difference between say... the Tamron SP 70-210mm f/3.5 (#19AH) and the 70-210mm f/3.5-4 (#46A) in relation to the 'Modern Photo.' quoted charts contained in the tests/descriptions.

Can anyone shed some light on this please?
Bob Atkins
Hero Member
Posts: 1253

Re: Lines per mm. in relation to magnification factors.
« Reply #1 on: January 04, 2009, 10:48:20 AM »

There should be no significant difference.

Lens performance is usually weakly linked to focus distance. A lens may perform better when focused at infinity the when focused at 3ft for example. Magnification ratio depends on focus distance, but the difference between 48:1 and 50:1 is so small that you would not expect resolution to me measurabley affected.

BTW your link doesn't lead to a valid page on that website, but I'm pretty sure that I understand correctly what you are seeing there.
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