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ND4 filter question


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#1 Patrick Barry

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Posted 12 March 2010 - 12:23 PM

Ok, so here goes a pretty dumb sounding question that I will ask anyway. If I pop an ND4 filter onto my lens, and the exposure would normally be an 11, do I count that stop (the 11) as one of the 4 stops down? If that makes sense?

Would it be a 4 or a 2.8.

Thanks guys!!
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#2 Brian Drysdale

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Posted 12 March 2010 - 12:52 PM

It actually reduces by 2 stops, the 4 refers to a 1/4, so at f11 you'd open to f5.6 with the filter on.

This explains the method used for defining ND filters.

http://www.cs.mtu.ed.../filter-ND.html
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#3 David Mullen ASC

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Posted 12 March 2010 - 12:52 PM

Ok, so here goes a pretty dumb sounding question that I will ask anyway. If I pop an ND4 filter onto my lens, and the exposure would normally be an 11, do I count that stop (the 11) as one of the 4 stops down? If that makes sense?

Would it be a 4 or a 2.8.

Thanks guys!!


I don't know why, but the still camera filter market is now using "ND4" to mean a 2-stop ND and "ND8" to mean a 3-stop ND -- I guess because a filter factor of 4 is 2-stops and a filter factor of 8 is 3-stops.

In cine terms, a 2-stop ND would be an ND.60 and a 3-stop ND would be an ND.90.

So an ND4 filter would mean you'd have to open from f/11 to f/5.6 to compensate.
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#4 Eric H

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Posted 12 March 2010 - 01:00 PM

I don't know why, but the still camera filter market is now using "ND4" to mean a 2-stop ND and "ND8" to mean a 3-stop ND -- I guess because a filter factor of 4 is 2-stops and a filter factor of 8 is 3-stops.

In cine terms, a 2-stop ND would be an ND.60 and a 3-stop ND would be an ND.90.

So an ND4 filter would mean you'd have to open from f/11 to f/5.6 to compensate.


someone, somewhere is going to get a nasty surprise one morning in telecine......my suggestion to anyone who's not sure, is to run your spot meter thru anything that might require compensation...if you don't have a spot meter then use your still camera and watch the number of stop loss the meter says when you put your filter in front. If you use the camera method be sure to use a uniformly lit object, like the sky or the white cyc/limbo in a studio, or a grey card.

good luck,
Eric
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#5 Patrick Barry

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Posted 22 March 2010 - 08:20 PM

Thanks all! That certainly explains a lot! :)
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