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05-07-2010, 03:34 PM   #1

Join Date: May 2010
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Confused on NDF and ring size

I'm a complete novice when it comes to SLR photography and lenses.. Through my online research I've discovered I'll need a NDF to do what I want to do.. now the question.. I look on sites that sell Filters and they all have various sizes - how do I know which to get?

I have a Pentax Kx with only the 18-55mm kit lens for the moment. I see it zooms to 55mm but I don't think I need a 55mm sized NDF.. or do I? I also see a 52mm on it with an icon of a circle with a line through it (Greek Phi??). I'm guessing that is the correct number to look at when matching filter size, but I wanted to confirm before spending money on this stuff.. surely someone here knows the answer. Please pardon my ignorance :c )

05-07-2010, 03:59 PM   #2

Join Date: Feb 2009
Location: Alameda, CA
Posts: 3,196
The "size" of the filter you want is the "filter thread size" of the lens, not the focal length or focal length range.

In your case, 18-55mm is the focal length range of the zoom lens, and 52mm is its filter thread size.

Short answer: you need a 52mm filter for that lens.
05-07-2010, 04:21 PM - 1 Like   #3
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Join Date: Nov 2009
Location: adelaide
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Hi mee
the circle with the line is the mathematical abbreviation for Diameter the number is the size eg 49 mil diameter= your filter size when rou purchase your next lens it may have a 55 or 77 diameter so you will need a different filter to fit.
05-07-2010, 06:34 PM   #4

Join Date: May 2010
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Original Poster
Thanks guys.. knowing is half the battle... :c D


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