# Filter exposure guidelines for B&W film.

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• 01-30-2014, 06:46 PM
markbarendt
Also negatives are very forgiving, with all the films I use I can get good prints from film shot 1-stop under to 2-stops over my target exposure.
• 01-30-2014, 10:00 PM
brian steinberger
Quote:

Originally Posted by Alan Klein
Good points all. Well I'm going to go ahead and try all three on the same subject with blue skies and clouds and bracket them as well and see what happens. Should I bracket +1 and -1 or +2 and -2?

This may be a fine way to learn. Make sure you take a shot without filter in place as we'll so you can see what's going on in the scene.

One test I did one time was take a gray card out on an overcast day and fill the frame mostly with it and take a shot, metering off the card (make sure there is no glare on it). Then put each filter on and start with the manufacturers filter factor, then bracket + - 1/2 stop in each direction. For the red filter maybe bracket up to +1 as a red usually needs more. Make sure you keep detailed notes. Then contact print your set of negatives and find the shot with each filter that best matches the unfiltered shot of the gray card. This test can be interesting but then again you're shooting under overcast light which is slightly bluish. Alternatively you could shoot this test on a sunny day but then you introduce color temperatures from different times of day. See how you can overthink this??
• 01-30-2014, 10:32 PM
StoneNYC
Quote:

Originally Posted by markbarendt
Like Bill says this is for external meters.

The math is easy, just use the filter factor as the denominator and the film's box speed as the numerator. The result is the ISO number you use to set your meter.

So for Tmax 100; film speed of 100 over a factor of 2 means you set the meter at ISO 50 (100/2=50). For filter factor 5; 100/5=20.

For Tmax 400 and an orange filter; 400/4=100.

I never knew this!!!

No wonder some I've my exposures always seemed off, I always thought filter factors were STOPS...

Kind of stupid, why make you do math instead of just putting the stops on the filter? I'm sure it "all goes back to xxxxxxx reason" it's still annoying and dumb.

Thanks for the info
• 01-30-2014, 10:39 PM
MattKing
Quote:

Originally Posted by StoneNYC
I never knew this!!!

No wonder some I've my exposures always seemed off, I always thought filter factors were STOPS...

Kind of stupid, why make you do math instead of just putting the stops on the filter? I'm sure it "all goes back to xxxxxxx reason" it's still annoying and dumb.

Thanks for the info

It isn't as stupid as you say.

The filter factors work well with ASA/ISO/EI numbers.

They work well with flash guide numbers.

They work well when you use more than one filter.

They work well with films that have different daylight and tungsten speeds.

They work well with calculations concerning bellows extension.

They fit well within a system.
• 01-31-2014, 12:20 AM
StoneNYC
Quote:

Originally Posted by MattKing
It isn't as stupid as you say.

The filter factors work well with ASA/ISO/EI numbers.

They work well with flash guide numbers.

They work well when you use more than one filter.

They work well with films that have different daylight and tungsten speeds.

They work well with calculations concerning bellows extension.

They fit well within a system.

Thanks, I cheat so much with bellows extension (without the reciprocity timer app I would be completely lost as far as bellows go) so I wouldn't know how to properly use the filter factor for that.

The strange part is, somehow all the times I've "incorrectly" used the yellow and red filters, somehow I still exposed relatively correctly and almost always happy with the image. Hmmm... :-0
• 01-31-2014, 04:53 AM
markbarendt
Quote:

Originally Posted by StoneNYC
The strange part is, somehow all the times I've "incorrectly" used the yellow and red filters, somehow I still exposed relatively correctly and almost always happy with the image. Hmmm... :-0

Not strange, it's more likely that your guesses are just doing a decent job of getting your shots inside the film's normal latitude range.
• 01-31-2014, 06:57 AM
RalphLambrecht