Yellow filter and Light metering in B/W

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I understand that in order to get correct metering I have to place this http://www.fedka.com/catalog/product_info.php?cPath=40&products_id=162
yellow filter over the light meter. The problem is the filter is smaller than the Leningrad's cell. How do I need to use it, and does it require being used with the meter (is there a formula that eliminates the placement of the filter over the meter)?

Thank You

 

[Xmas]

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It depends on the film type and the filter type, some filters will have a x2 on the rim, that would mean that you either

open up one stop (f/ number) or
use next slower speed.

So approximately

very faint yellow 0.7
medium 1
deep 1.5

stop in each case

Noel

 

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The x2 example would only apply to pan film,

ortho would need x4 (or more) with the same filter
infrared less

Depends on the exact spectral sensitivity, the film manufacturer should provide graphs and suggestions for each filter type, for each film.

Noel

 

[Rob-F]

Yes, the link you provided does indicate that it has a 2x filter factor. So, that is the place to start. Open up one stop for an average scene. But how much you should open up also depends on the color of the subject. Filters freely pass their own color. So when the subject is yellow, very little filter factor is needed--perhaps none at all. or only 1/4 stop. Too much increase, and you will negate the purpose of the filter--and probbably overexpose the subject. If that yellow subject is against a blue sky, and you only allow 1/4 stop factor or less, you will get a nicely darkened sky, as well as a properly exposed subject.

 

[richard_l]

If you are going to use the same filter for several frames, the easiest thing to do is to divide the film speed by the filter factor and set the meter accordingly. So if it is a 2x filter and the film speed is 400, reset the meter to 200. Just remember to set the film speed back to 400 when you take off the filter.

Richard

 

[richard_l]

Since some people don't like my logarithmic formulas, here's a table of some filter factors and equivalent f-stop corrections. (+n means open up n stops.)

1.2x (+1/3)
1.4x (+1/2)
1.5x (+2/3)
2x (+1)
2.5x (+1 1/3)
2.8x (+1 1/2)
3x (+1 2/3)
4x (+2)

******Stop here if allergic to logarithms***************

For any filter factor k (written kx), the f-stop correction is log(k)/log(2).

Richard

 

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Thank You Very much, all, for your advice.