Help on close-up and ND filters


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darkness

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Aug 11, 2002
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#1
I understand that close-up filters are used to shorten focal length so that you can focus an object closer, and ND filters are used to decrease the amount of light.

Here's the technical part: what is the meaning of those +1, +2, +4, etc. for close-up filters? How does it affect focal length in equations? For ND filters, what is x1, x2, x4, etc.?? Do they correspond to the number of stops of light that they block out? Thanks for any help rendered!
 

NitroTech

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Apr 4, 2002
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#2
Originally posted by darkness
I understand that close-up filters are used to shorten focal length so that you can focus an object closer, and ND filters are used to decrease the amount of light.

Here's the technical part: what is the meaning of those +1, +2, +4, etc. for close-up filters? How does it affect focal length in equations? For ND filters, what is x1, x2, x4, etc.?? Do they correspond to the number of stops of light that they block out? Thanks for any help rendered!
http://www.photographytips.com/page.cfm/35

see whether this will help for the ND filter qn.
 

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