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grey filters

Alain Jacques RIO , Dec 26, 2011; 01:34 a.m.

About Hoya or B+W grey filters, where can i find indications about correction of exposition, in stops, for the different references, for example : Hoya ND4 - ND8 - NDX400
I would like to loose about ten stops
Thanks for your help


Bob Sunley , Dec 26, 2011; 01:55 a.m.

Here is one chart http://www.photofilter.com/hoya_factor.htm
You would need three ND8 filters for 9 stops, B+W do a ten stop ND filter, you can find it on BHPhoto's web site.

Alain Jacques RIO , Dec 26, 2011; 06:36 a.m.

Thank you for your help Bob, but for ten stops B+W grey filter, what is the reference ? not any web site give the indication.

Jim Momary , Dec 26, 2011; 08:00 a.m.

B&W catalog -
... found by Google search "B&W neutral density designation"
Happy New Year
Jim in NJ USA

David Henderson , Dec 26, 2011; 09:18 a.m.

You'll get there in about 3 clicks on the B+W site once you realise that they aren't called "Grey" filters but Neutral Density Filters or ND filters for short. The only supplier afaik who use the term grey for what you want is Cokin, whose products are far enough away from neutral not to risk that nomenclature. Two further points

  • Its pretty common to get some sort of colour cast with these filters no matter how well made and how expensive. Naturally its more of a problem for colour film users whose work isn't digitised before printing.
  • You can often get substantially lower prices than those on the B+W site by looking around

Alain Jacques RIO , Dec 26, 2011; 04:06 p.m.

Thanks to everybody for your Help
Happy new year

Alan Marcus , Dec 26, 2011; 07:39 p.m.

Gray filters are called Natural Density Filters
The values you are asking about are called Filter Factors
(FF). This is a number used as a multiplier to compensate for light energy loss as the light waves transverse the filter. Often these filters are labeled using a different system called density. The density value is written as a decimal fraction.

TABLE Density to Filter Factor (FF) with light reduction in f/stops

0.30 = FF 2 = 1 f/stop reduction
0.60 = FF 4 = 2 f/stop reduction
0.90 = FF 8 = 3 f/stops reduction
1.20 = FF16 = 4 f/stop reduction
1.50 = FF 32 = 5 f/stop reduction
1.80 = FF 64 = 6 f/stop reduction
2.10 = FF 128 = 7 f/stop reduction
2.40 = FF 256 = 8 f/stop reduction
2.70 = FF 512 =9 f/stop reduction
3.00 = FF 1024 = 10 f/stop reduction

Jay Drew , Jan 01, 2012; 08:07 p.m.

Hi there Alain
I'm sure you must have good reasons to want a 10 stop reduction, but man, that's a bunch. The most I've ever needed was about 6 stops. (which I don't have, but I got by.) I'm curious why you would need such a dense ND filter. I think that's about what welders use.
Happy New Year, JD

Alain Jacques RIO , Jan 01, 2012; 09:42 p.m.

Thanks for your answer JD.
I need a 10 stops reduction filter to take photos with about 4 to 8 seconds exposure, to get the water flat, i tried with a 2 grey filters, 2+3 stops reduction, and it was not enough.
I founded the refernce i was looking for, i ordered it, i will see.
Happy new year too

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