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Filter factor for Wratten 25 47 61


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#1 Brian Rose

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Posted 05 October 2006 - 04:40 PM

All,
does anyone know off the top of their head what the filter factors are for the wratten 25, 47 and 61?

Thanks!
Brian Rose

Sorry, that was wratten 24, not 25
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#2 Mike Rizos

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Posted 05 October 2006 - 06:58 PM

Hi Brian

I think they are 8, 4, and 4. I'm not sure of the 24, but it must be very close to 25. One sure way to find out is to measure through them with a light meter or an SLR.
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#3 Dominic Case

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Posted 06 October 2006 - 12:12 AM

Brian, you seem to be following the same line through two different threads - with half the information in each. Not helpful.

I asked you in your thread about 'colour through black and white' what filters you were using for colour separation photography. I guess this thread gives the answer. Wrattens 24 (Red) , 47 (Blue), 61(Green).

Incidentally, the 25 is the better tricolor filter, but there isn't much difference between it and the 24.

In daylight (D65), the 24 transmits 17% luminance, The 47 transmits 2.6% luminance, and the 61 is 20% luminance - according to Kodak's filter manual.

However, those take ino account the contribution to total luminance, rather than the simple proportion of light.

The normal photographic factor of a 24 is x8, a 47 is x6, and a 61 is x12

These factors would correct a single exposure of a neutral greyscale back to a normal density.

When you combine the images (are you doing this in Photoshop?), you need to take 33% of each image (or different proportions, haven't thought that one through yet, but they need to ad up to 100%.
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