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Thread: Error in filter factoring?

  1. #1

    Error in filter factoring?

    Being new to LF, I started reading Steve Simmons' book on using view cameras. H e recommends holding the filter in front of the exposure meter when taking readi ngs, and then adding a filter factor to the exposure determined from the reading (p,28, rev. edit.). What am I missing? Doesn't this method add the filter fact or twice? Is this idea of holding the filter in front of the meter a good metho d to use?

  2. #2
    Whatever David A. Goldfarb's Avatar
    Join Date
    Mar 2000
    Honolulu, Hawai'i

    Error in filter factoring?

    That looks like a proofreading error to me. Yes, that would be adding the filter factor twice.

    You could use the method of holding the filter in front of the meter with a spot meter or other reflective meter, but obviously not with an incident meter with a dome-type diffuser. There might sometimes be differences, though, between the spectral sensitivity of the meter and the spectral sensitivity of the film, so it isn't a bad idea to do your own tests with different films and light sources, or use the factors recommended on the film's technical data sheet, usually available on the manufacturer's website.

  3. #3

    Join Date
    Dec 2001

    Error in filter factoring?

    Doing that would cause you to add the filter factor twice. Either you can meter through the filter, or you can meter and then add the filter factor, but not both at the same time. I don't meter through the filter. I meter without it, and the add the filter factor. Sometimes I even remember to NOW put the filter on the lens. I'm almost as bad about that as I am about remembering to pull out the darkslide. But I still somehow manage to muddle through it

  4. #4

    Error in filter factoring?

    Probably this second factor is "Hutchings Fudge Factor" (a la Gordan Hutchings). The concept is that the meter does one thing but it is not enough perceptually. The HFF is different for different filters right? As low as zero for some filters as I recall even if the filter's own factor is not zero. My HFF chart is in my camera case but from memory the highest HFF is less than 2x. It is not a typo.

    As far as metering through the filter: that is a good idea especially if you are out under strange light (e.g., early, late, stormy etc.) but usually I just use the filter's published factor and usually use the HFF too.
    John Hennessy

  5. #5

    Error in filter factoring?

    Hi Richard,

    I have always heard that since meters do not 'read' color and light the same way film does (particularly films like infrared, or polarlizing filters), one is best off using the published filter factor, rather than what the meter says... My own experience has affirmed this.


  6. #6

    Error in filter factoring?

    you can do it that way but the best way is to take a zone V shot with your filters and then read which negative has the correct density. For example when I use a red filter, although the published factor is 8x I use 3 and 1/2 stops instead of 3 stop, because when I took a pic of a gray card the negative that most closely came to a density of .65 for Zone V was the one with 3 and 1/2 stops more exposesure, not 3 as specified by manufacturer. Until you do a personal test you will always have a little bit of fudge factor built in.

  7. #7

    Error in filter factoring?

    but isn't the reason we have to use filter factors based on the idea that the filter subtracts that particular color from the scene when put to film? How could the filter factor always be the same since that same color is not equally present in every scene.

  8. #8

    Error in filter factoring?

    Exactly Mark that is why you test with a neutral gray subject! This way you can see how much light is being substracted without worrying about the color.

  9. #9

    Error in filter factoring?

    Jorge, are you saying you carry a grey card around with you and check it every time? or test once with grey card and then use that correction every time. frankly neither is very accurate since the color that you filter for will be different at every shooting session and will be different where you are as opposed to where your subject may be. why not just get an adjusted meter (zone 6) which makes a world of difference and not have to ever worry about it?

  10. #10

    Error in filter factoring?

    I disagree with you Mark, it is the most accurate way to test filter factors. I guess I will have to explain the method, I thought it was evident. Ok, I take a red filter, focus on a gray card and take 3 sheets of film, one at the manufacturers recommended factor, one at 1/2 stop over and one at 1/2 stop under, the one that comes closer to the zone V density (0.65)is my "corrected" factor. SInce you have no color you are only measuring light absorbtion by the filter. Once you are taking a real subject you are correct, some colors get absorbed and some get through the filter, but remember in adition to this phenomena there is an even amount of light absorbtion across the spectrum, which is why we use the factors. Look if you wish to continue using the factors it is not a bad way to go, but if you ever come across underexposure or overexposure you will remember what I am telling you.

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