Confused on NDF and ring size

mee · 05-07-2010, 03:34 PM

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 )

SOldBear · 05-07-2010, 03:59 PM

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.

wedgetail · 05-07-2010, 04:21 PM - **1 Like**

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.

mee · 05-07-2010, 06:34 PM

Thanks guys.. knowing is half the battle... :c D

05-07-2010, 03:34 PM	#1
mee Veteran Member Join Date: May 2010 Posts: 7,403	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 )

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05-07-2010, 03:59 PM	#2
SOldBear Veteran Member Join Date: Feb 2009 Location: Alameda, CA Posts: 3,206	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
wedgetail Senior Member Join Date: Nov 2009 Location: adelaide Photos: Albums Posts: 211	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
mee Veteran Member Join Date: May 2010 Posts: 7,403 Original Poster	Thanks guys.. knowing is half the battle... :c D