[pure-silver] Re: filter factor

  • From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
  • To: PureSilverNew <pure-silver@xxxxxxxxxxxxx>
  • Date: Fri, 29 Sep 2006 23:10:53 +0200

Richard is right that the filter factor depends on the 'color' being
photographed. A contrast-enhancing filter would not work as intended if it
would have the same filter factor for all colors, it would just be a neutral
density filter.

Nevertheless, assuming the aim is ONE average filter factor, the method
proposed by Dave works well. To see the effect and the filter factor, one
can photograph something like the Kodak Color Separation Guide and Gray
Scale with and without the filter. It will tell you the effect of the filter
on each color and the average gray. The resulting filter factor works for
all average cases.





Regards



Ralph W. Lambrecht

http://www.darkroomagic.com







On 2006-09-29 22:47, "Dave Valvo" <dvalvo@xxxxxxxxxxxxxxxx> wrote:

> The correct way to determine a filter factor is to photograph an 18% grey
> card with and with out the filter.  Then measure the density of each image
> and determine the LogE difference from the D-logE curve you would get from
> the process because how you process is important.  Now who is going to do
> that?    Meter reading is Kentucky windage.  Works for me as I get older.
> 
> Dave
> 
> ----- Original Message -----
> From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
> To: <pure-silver@xxxxxxxxxxxxx>
> Sent: Friday, September 29, 2006 3:56 PM
> Subject: [pure-silver] Re: filter factor
> 
> 
> Since I don't know what brand meter you have or its age, let me warn
> that trying to determine your own filter factor is iffy because your
> meter's sensor may not be equally sensitive to all wavelengths.  This
> was a problem years ago when SLR's first started including meters.
> Metering with the filter in place often produced the wrong exposure.
> Today's meters have a better spectral response.
> 
> Jerry
> 
> -----Original Message-----
> From: pure-silver-bounce@xxxxxxxxxxxxx
> [mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Shannon Stoney
> Sent: Friday, September 29, 2006 3:09 PM
> To: pure-silver@xxxxxxxxxxxxx
> Subject: [pure-silver] filter factor
> 
> 
> I just bought a Hoya yellow K2 filter for a view camera lens.
> (Luckily it also fits my medium format camera.) I held it up in front
> of the spot meter today while metering  shadow areas, and it read a
> third of a stop less than without the filter.  So, does that mean my
> filter factor is 1.3?
> 
> --shannon
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