Filter exposure guidelines for B&W film.

Discussion in 'Exposure Discussion' started by Alan Klein, Jan 29, 2014.

  1. Alan Klein

    Alan Klein Member

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    I normally shoot color film but decided to try B&W. I just picked up filters and Tmax 100 film to use with my landscape pictures.

    What are the recommended stop adjustments for each filter below? Here are the factors given by the manufacturer. All filters are B+W MRC F-Pro's.

    Yellow 022M filter factor is 2. f/stop ______?
    Orange 040M filter factor is 4. f/stop _______?
    Light Red 090M filter factor is 5. f/stop ______?

    There's another darker red that has a factor of 8. What's its f/stop? ________? Is this one overkill? ___________?

    If I add a polarizing lens, are the f/stop adjustments additive or do you multiply them? ____________?

    Beside the recommended f/stops, any other recommendations you'd like to pass on that would help me? ______________?

    Thanks Alan.
     
  2. Bill Burk

    Bill Burk Subscriber

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    Yellow 022M filter factor is 2. f/stop ___1___?
    Orange 040M filter factor is 4. f/stop ___2____?

    There's another darker red that has a factor of 8. What's its f/stop? ___3_____?

    This is after metering outside the camera. If you meter with the filter on the camera, you open a whole ball of wax.

    There's a set of factors called "Hutching's Filter Factors" that you apply after metering throught the filter... The gist of it is ... a meter will tell you that red filter only needs 2 stops... but in reality you need 3 stops because the shadows ... which are mostly lit by reflected light from the blue sky... are metered wrong and will be really underexposed if you don't give it extra exposure.
     
  3. Gerald C Koch

    Gerald C Koch Member

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    It is not recommended to use more than a single filter since each one degrades the image. If you must use a filter then buy the very best that you can afford. Remember you are putting something in the optical path. You want to hold any degradation of the image to a minimum.

    Usually filters are not needed except in certain circumstances. A yellow, orange or red filter will emphasize clouds since they darken the rendition of the sky. A green filter will help open up shadows outdoors.
     
  4. BradS

    BradS Member

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    filter factor 5 equates to 2.3 stops (2 1/3 stops)
     
  5. markbarendt

    markbarendt Subscriber

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    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.
     
  6. Dr Croubie

    Dr Croubie Member

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    Or to use the more complicated maths: 2^stops=factor. ie:
    2^1 stop = factor 2
    2^2 stops = factor 4
    2^3 stops = factor 8
    etc.
     
  7. David Allen

    David Allen Member

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    Filter factors are simply guides as to how much exposure compensation they MAY require. The actual compensation will be dependent upon the prevailing colours in any given scene and the prevailing colour of the light (dependent upon time of day / sun's position / time of year). The best way of working with filters is to use a hand-held meter that responds to light in a similar manner to film (selenium cell meters are the best and you need to be aware that some early CDS cell meters from the 1960s do not respond to light in a predictable manner).

    You simply meter the scene, note the exposure, and meter again with the filter in front of the metering cell and note the difference in exposure. You will then find that any given filter will require an exposure compensation that rarely matches it's filter factor. For example, a yellow filter with filter factor 2 may require anything from 1/2 to 2 stops compensation.

    Bests,

    David
    www.dsallen.de
     
  8. R.Gould

    R.Gould Member

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    Taking an iso 100 film as an example, with a yellow filter set the meter for 50 iso, for an orange filter set it to 25 iso, and for a red filter set the meter at 12, that is, a yellow filter needs 1 stop more, a orange 2 stops and a red or green needs 3 stops more, this is a quick and simple method of taking filter factors into account, but it has served me well for as long as I have been taking photographs
     
  9. brian steinberger

    brian steinberger Member

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    I simply meter through filters with my Pentax digital spot. Been doing it this way for years with great results. I very often will stack an orange and polarizer. That's my favorite combo. If I'm shooting using in camera metering (rangefinder, not TTL metering) I just dial in +3 stops and go. A lot of this comes from experience. You will learn as you go. I find filter factors mess up my way of thinking. I just memorized over the years how many stops each of my filters eat up, but meter through them most of the time just to be sure, as was said above, in different light filters respond differently.
     
  10. Alan Klein

    Alan Klein Member

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    Thnaks for the input. Now I know why I was getting different stop answers from the web. A lot of it "depends".

    Just one note. The red filter I bought was a light red filter factor 5. B+W has a dark red with factor 8. Do people use the dark red filter more than the light red I got and should I replace the light with the dark before I open the box and can't return it?
     
  11. Regular Rod

    Regular Rod Member

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    http://en.wikipedia.org/wiki/Filter_factor

    It's all there.

    BUT... Mark has given you the best answer.

    f
    stops is a stupid way to compensate. It is duration of exposure we will mostly be interested in if we want to retain depth of field...

    RR
     
    Last edited by a moderator: Jan 30, 2014
  12. DREW WILEY

    DREW WILEY Member

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    There are indeed plenty of tech sheets out there. But for TMax films, to keep it simple in daylight, for lt yellow or lt yellow-green, I just round the compenstation to 1 EV (either one speed slower or one stop wider open), for moderately deep green or red-orange, 2 EV,... for no.25 true red, 3 EV. I'd avoid a 29 red because it's harder to view thru and won't add much, unless you're aiming for something between red and IR, but it would also amt to 3EV with these particular films.
     
  13. brian steinberger

    brian steinberger Member

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    I change shutter speed stops, not aperture to retain depth of field. It's easier for me to remember how many stops of light a filter eats up then to remember what new ISO my film becomes each time I put a filter on. But to each their own. There are many ways to skin a cat!
     
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  15. Alan Klein

    Alan Klein Member

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    Interestingly, the B+W 90 light red (same as 25) I bought has a filter factor of 5 while their dark red 091M (same as 29) has a filter factor of 8. It seems their filter let through more light than the filter chart.

     
  16. DREW WILEY

    DREW WILEY Member

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    To pin all this down precisely you have to do a series of controlled tests under specific light conditions with specific films, then measure the
    result with a densitometer. Not all pan films are by any means identical with respect to spectral response. Some have a little more sensitivity
    in the red, while others have less, and something like ACROS is technically an orthopan, with decreased red sensitivity. These kinds of differences will determine whether the factor is the same for a 25 and a 29, whether they are different, or whether a 29 just lops an entire zone from the shadows, as in ACROS, where use of one is counterproductive. Similarly, slight differences exist with respect to blue and green sensitivity, which all gets tangled up with significant color temp differences, esp apparent at high altitudes under blue skies. On and on. For critical work in the lab I measure each of these factors. In the field it will drive you nuts, and for most black and white applications, being a third stop off here and there isn't going to have much practical significance. There are also slight differences with respect to how different
    manufacturers label their filters. But to say f-stops are never useful for controlling the correction factor is misleading, particularly when recip
    factors come into play at long exposures, or subject movement mandates keeping shutter speed up, or the ability to handhold a camera in
    the case of small formats. We have choices and use them wisely, depending on specific circumstances.
     
  17. Alan Klein

    Alan Klein Member

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    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?
     
  18. markbarendt

    markbarendt Subscriber

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    The only reason I would bracket is if I was doing a test or if I thought my subject blinked.
     
  19. Alan Klein

    Alan Klein Member

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  20. DREW WILEY

    DREW WILEY Member

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    Metering thru a filter tells you how the spectral sensitivity of your meter senses a luminance chance, not how the film itself sees the difference.
    That's why Fred Picker marketed a modified Pentax Spotmeter with a special filter pack in its to correct the sensitivity to "normal" panchromatic
    film, whatever that meant. So that idea might have improved certain scenarios but not others, because not all films are the same. After awhile
    this all just starts going around in circles anyway. A little bit of practice shooting and printing with specific films, with specific filters, and
    it starts getting real instinctive. So I guess the moral of this story is, don't carry more filters than you actually need, and don't worry too
    much if your factor isn't hypothetically dead-on.
     
  21. markbarendt

    markbarendt Subscriber

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    Composition problems or subject problems are far more likely for me than exposure errors. I don't think I'm odd in this respect either.

    So rather than bracket, I like to spend my extra film and time alternative compositions or poses.
     
  22. markbarendt

    markbarendt Subscriber

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    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.
     
  23. brian steinberger

    brian steinberger Member

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    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??
     
  24. StoneNYC

    StoneNYC Subscriber

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    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
     
  25. MattKing

    MattKing Subscriber

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    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.
     
  26. StoneNYC

    StoneNYC Subscriber

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    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