Filter factor and hand held meter.

Discussion in 'Exposure Discussion' started by Mike Kennedy, Mar 15, 2006.

  1. Mike Kennedy

    Mike Kennedy Member

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    I will be testing 2 cameras in the next few days. Each are fully operational,except for their built in meters. Is there a way to adjust my hand held meter to compensate for the two filter's I plan on using?
    I am using a yellow K2 (filter factor of 2=1 stop) and red #25 (filter factor of 8=3 stops) in conjunction with a vivitar reflective meter and grey card. Shooting Tri-X so I have lots of latitude. Tested the meter with my Nikon FM2 and it's within 1/3 stop.
    It would be so much simpler to adjust the meters ASA to compensate for the loss of light. The solution is probably a simple one but I am suffering from early morning "Brain Freeze"...........need more coffee.

    Thanks Much.
    Mike
     
  2. Soeren

    Soeren Member

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    Meter with the respective filter in front of the cell. Try it out and compare with your FM2
    Or ditch one of the filters and dial the compesation in on the ISO on your
    meter.
    You could make a chart. compensate one stop on your meter for Yellow. The chart then takes care of the two other stop (of the 3) for red
    NF->Y->R
    32->22->11
    22->16->8
    16->11->5,6
    11->8->4
    8->5,6->2,8
    5,6->4->2
    4->2.8->1,4
    you could do something similar for Shutterspeeds.
    Brain Freeze and Exposure calculations are imcompatible :smile:
    Cheers Søren
     
  3. Nick Zentena

    Nick Zentena Member

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    Divide the film speed by the filter factor.
     
  4. Mike Kennedy

    Mike Kennedy Member

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    Thanks Soren, thanks Nick.
    I can't even tie my shoes before I have at least 2 cups of "joe" in the early A.M.

    Mike
     
  5. bikegeek76

    bikegeek76 Member

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    am i all screwedup then?

    I have a red 25 with my 35 and my 6x6. It is a non issue with my 35 because it is ttl. However, I was operating under the assumption that a filter factor of 4 meant compensate by 4 stops. my 6x6 is an old tlr, so I hand meter everything. Can anyone set me straight?
     
  6. Bill Mitchell

    Bill Mitchell Member

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    The filter factor is how much you have to increase the timing to get the correct exposure. It is what you multiply the shutter speed by to get the correct exposure. Thus FF=2 means giving TWICE the exposure (1/30 instead of 1/60 -- 2x1/60 =2/60 = 1/30). This is ONE stop. Likewise FF=4 means four times the exposure, or TWO stops. Also, don't trust your TTL metering to give the correct exposure with filter attached -- the brain must be used at least a little (if possible).
     
  7. JBrunner

    JBrunner Moderator Staff Member Moderator

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    Yes, correct. The TTL meter may or may not read correctly due to the meters individual spectral sensitivity.
     
  8. noseoil

    noseoil Member

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    When in doubt, I usually meter the gray card with a filter in place. This seems to give me the best results, as it (normally) isn't affected by color sensitivity. Usually, a bit more exposure works better than a bit less, if a guess is involved. Take notes to make sure the "guess" was correct when the print is finally made. tim
     
  9. Bruce Osgood

    Bruce Osgood Membership Council Council

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    What Bill Mitchell says I believe is correct also. But when you want to keep the shutter speed and adjust the f-Stop you would apply the SqRt of the Factor. For a FF of 4X the SqRt is 2. You would then open the shutter 2 stops. I find either of these methods to be better than using the filter in front of the meter or lens.
     
  10. Donald Miller

    Donald Miller Member

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    A more accurate means of assessing filter factors is to check their spectral response on a color densitometer. While not totally accurate, it is more accurate then any other method that I have tried.

    For instance a #12 yellow may have an affect of 3 stops on a cyan or blue object like the sky but it may have a 1/3 stop effect on the straw of a ripened wheat field.

    A #25 red may have a five stop effect on a blue or cyan sky but only 2/3 stop effect on a freshly painted red barn.

    No filter has an actual effect of lightening the same color. It is only in relation to other colors that the appearance is one of lightening. The contrast created by decreasing exposure and hence darkening the opposing color is responsible for the appearance of lightening.

    Published filter factors are based on averages. Not too many exposures fit these averages.

    This approach takes a little more work and a little more mental activity at exposure but the results are much more predictable.