Filter exposure compensation

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atlcruiser

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I just ordered a few flters and wanted to get some info on how to compensate for the filter while setting exposure. I have searched and read a bit but overall I would say I am just a tad confused :)

I have:
#13 GREEN 2
Leica 39 MM GREEN GLASS FILTER

RED-ORANGE #041 (22)
#23A LIGHT RED

Y48 (MED YELLOW)
MED. YELLOW #022 (8)

I bought doubles as my CV is 52 and the Leicas are 39MM:mad:

Using an M4-P with 'cron 50/2, CV 35/1.4 and Hector 135mm/4.5
for now it will all be tri x 400....

Thanks in advance
david
 
Dear David,

Alas it varies from film to film and filter to filter (and indeed according to subject)!

Starting points are pale yellow 1.5x, medium yellow 2x, dark yellow 3x; light red 3x, deep red 8x; greens, 2-4x... With current Tri-X I'd consider 2x yellow, 4x red, 3x green. But those are generalizations.

Cheers,

R.
 
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Maybe this is where i am getting lost....forgive my tardness :)
3x=1.6 stops more open?
4x is 2 full stops open?

What is the conversion being done here?



delft said:
From http://www.rodenstock-photo.com/mediabase/original/e_Rodenstock_Filters_63-73__8228.pdf and http://www.astronomica.co.uk/index....ters/Wratten-23A-Light-Red-Colour-Filter.html:
3x (1.6 stop) for the green,
4x (2 stops) for the (red) orange #22 and probably the 23A too,
2.5-3x (1.3 - 1.5 stops) for the med. yellow
You might need to do some experiments, as the factor will also depend on the lighting and the spectral sensitivity of the film/sensor.

Dirk
Click to expand...
 
Roger Hicks said:
<snip>
Alas it varies from film to film and filter to filter (and indeed according to subject)!

Starting points are <snip> But those are generalizations.

<snip>
Click to expand...

Roger has it right. Filter factors are no more absolutes than film speed or "the correct exposure". Like a light meter, filter factors are a starting point that will either get you close enough (normally) or a place to begin to exercise judgment.
 
It is confusing, and unnecessarily so to my mind. I wish the filter makers would simply say "needs an extra stop, 2 stops, etc" instead of this filter factor deal. You'll have to devote a roll of film to shooting the filters w/ different exposures and make notes. When you get the film developed you'll be able to determine the best exposure. Then write how many stops you need on your filter box, or on a piece of masking tape and stick it to your filter case.
 
atlcruiser said:
Maybe this is where i am getting lost....forgive my tardness :)
3x=1.6 stops more open?
4x is 2 full stops open?

What is the conversion being done here?
Click to expand...

Filter Factors date from the age, long ago, when you rarely altered the lens' aperture when adjusting exposure. You would almost always only make adjustments by changing the exposure time. It was then convenient to mark filters with the "factor" for adjusting the exposure time. A factor of 2x means you doubled the exposure time (1 stop) while a factor of 4x meant 4 times the exposure time (2 stops).
 
Dwig said:
Filter Factors date from the age, long ago, when ...
Click to expand...

Actually, filter factors date from the age, long ago, when photographers knew how to multiply photographic exposure. ;)

Both Roger and Bob have it right that there are differences, &ct, etc.. but with the exception of transparency film and critical exposures most novices (and many experienced photographers) have successfully relied on broad film latitude to accomodate those differences.
 
Filter factor is simply the value one divides the film exposure index by to arrive at the proper starting setting for your exposure meter or flash calculator. So for instance, if you normally rate your film at 200 and are using a filter with a ff of 8, your starting EI becomes (200/8) or EI 25. Of course if you have TTL metering, you need not change your starting point. Adjustments in this case would be made using your exposure compensation control.

Filter factor is more confusing when not using a meter/flash calculator because one must think in stops or shutter speeds.
 
Roger Hicks said:
Dear David,

Alas it varies from film to film and filter to filter (and indeed according to subject)!

Starting points are pale yellow 1.5x, medium yellow 2x, dark yellow 3x; light red 3x, deep red 8x; greens, 2-4x... With current Tri-X I'd consider 2x yellow, 4x red, 3x green. But those are generalizations.

Cheers,

R.
Click to expand...

No kidding, you have to test each one, with every film, and maybe even with different cameras. Get a Dremel tool to inscribe the correction on the ring. I can never find my notes.
 
I am using an M4-P, a sekonic twinmate and a whold lot of broad latitude. Good thing I am doing my own development!

thanks for the help

Next novice question:
Justt wanna make sure on this :)

If i need to open 2 stops and i am using 400 film i can set my hand held meter to 100 speed and just follow the indicated exposure range. 400 - 2 stops equals 100 right? 400 - 1 stop would be 200.....?
 
If as you say you're away from TTL, yes.

But as filters for b&w alter some colors more than others, you'll be depending on how much you want to lighten or darken a precise part of your image, so testing is a good idea...

Cheers,

Juan
 
charjohncarter said:
No kidding, you have to test each one, with every film, and maybe even with different cameras. Get a Dremel tool to inscribe the correction on the ring. I can never find my notes.
Click to expand...

It's worse than that - different light has a different filter factor. Think of midday illumination of open shad - the light is very blue. A red filter would cut most of that light. Now shoot in the evening during the golden hour, when the light is a golden yellow. That same red filter will pass nearly all of the light, and thus have a much lower factor.
 
Chris101 said:
It's worse than that - different light has a different filter factor. Think of midday illumination of open shad - the light is very blue. A red filter would cut most of that light. Now shoot in the evening during the golden hour, when the light is a golden yellow. That same red filter will pass nearly all of the light, and thus have a much lower factor.
Click to expand...

Thanks, Chris... That's a clever observation, I had never thought of that!
 
To further amplify Chris101's point. I prefer to use a polarizing filter, it doesn't insure a dive in shadow values, and you still get a darkening of the sky. Metering a PF is the same test of your intelligence. I do use a yellow filter sometimes even if I want normal contrast, but I use my own compensation numbers to return some of the shadows.
 
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