Question about metering when using filters

Discussion in 'Medium Format Cameras and Accessories' started by Graham_Martin, Sep 4, 2011.

  1. Graham_Martin

    Graham_Martin Member

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    When using filters on my non-metered RB67 can I simply hold the filter in front of the meter in order to determine correct exposure? If not should I just stop down based on filter factors? If I recall correctly one can find a filter factor chart on the Ilford site.
     
  2. ann

    ann Subscriber

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    I tend to add the filter factor after metering the scene. however, this is one of those questions that will create opposite answers.

    Sort of like ford vs chevy.


    Each filter should have the filter factor listed on the container it came in.
     
  3. Ian C

    Ian C Member

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    I found that the built-in meters in my Nikons “see” color-filtered light differently than film.

    For this reason, I meter the scene without a filter and use the filter maker’s specification for the number of stops held back by the filter when setting exposure.

    Reckoning the adjustment in stops is more logical than using filter time factors. For example, if the factor was 2.5, there is no shutter speed that we can use to get that correction.

    A filter with a time factor of 2.5 holds back 1 1/3 stops. That’s easily set with a 1 1/3-stop aperture change or 1 stop of extra time plus opening the aperture by 1/3 stop.

    Black and White Filtering Notes ( Nikon EL2 + 55/1.2 AI Nikkor, ASA 100 sunlight, gray card)

    This is in the form: Filter, Δf, Δf meter

    Hoya K2 (8) yellow, 1, 0

    Hoya O(G) orange, 2, 0.6

    Vivitar 25A red, 3, 1.6

    Hoya X(0) yellow-green, 1.5, 0.5


    Hoya X(1), 2, 1.6


    The through-the-filter readings are too high in each case. The error varies with the filter color.

    Of couse, this problem doesn't affect handheld meters (unless you place a filter between the light and the meter's photocell).
     
  4. Steve Smith

    Steve Smith Subscriber

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    It does indeed. There are many methods and none are wrong. I compensate for the filter by adjusting the ISO on the meter. i.e. with ISO 100 film and an orange filter, I set the ISO on the meter to 25.


    Steve.
     
  5. pentaxuser

    pentaxuser Subscriber

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    I am surprised at the differences. Appreciable in every case. I have always relied on my Pentax in-camera meter getting it right or nearly right and most books seem to suggest that in-camera meters record the filters' affect accurately or reasonably so.

    I wonder if some cameras are better than others? I must check both my Pentax and see what happens.

    pentaxuser
     
  6. Ian C

    Ian C Member

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    I too was surprised by the difference. This experiment convinced me that I had to meter the scene without the filters or use an incident meter when using colored filters on my Nikon. This camera produces "spot on" transparencies with the built-in meter with UV, Skylight, or polarizing filters.
     
  7. grahamp

    grahamp Subscriber

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    If the meter cell has any colour sensitivity (or insensitivity) it will bias the reading. If the subject has a dominant colour that matches the filter it will inflate the reading, possibly leading to an underexposure (or vice versa). And this assumes that the film sensitivity is normal panchromatic. Filter factors should give a consistent exposure correction. Ideally you should compare the results of a filter factor exposure with a through the filter measurement and make your own corrections for the meter behaviour if needed.

    If you hold a filter in front of a meter you may be adding flare to the equation as well.
     
  8. Jeff Kubach

    Jeff Kubach Member

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    What he said!:smile:

    Jeff
     
  9. grahamp

    grahamp Subscriber

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    I have mild colour blindness, too. Fortunately I can tell orange/red from yellow/green!
     
  10. Christopher Walrath

    Christopher Walrath Member

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    The biggest thing with color filters is that, unless you are shooting a monotone scene, you will have varying local results in your negative. Let's assume a general landscape. Green grass and trees, blue skies with sparse clouds and maybe some darkish red or purple flowers to throw opposites into the scene. The temptation is to break out a yellow filter to accentuate the sky. This would darken the blue somewhat to make the clouds pop. This might also lighten the flowers a smidge in relation to the whole. But it will definitely brighten your greens. So you have one filter having varying effects of either transmitting or blocking the light. The filter factor is a general recommendation for adjustment and most times will not lead you wrong. But it does not hurt to take into account all changes to your subject area so you will better know what to expect of the result.
     
  11. Dan Daniel

    Dan Daniel Subscriber

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    Christopher Walrath makes a good point if one is fine-tuning exposures as with the Zone System or such. I did tests years ago determining the filter factor for various filters when shooting objects of different color. So I knew how far green would move with a yellow filter and what zone it would end up it, where red would be, where blue would be.

    Fortunately, with some therapy and proper medication, I stopped this kind of silliness :smile: A little attention and taking notes of expected and actual results for a few rolls of film should dial in all you need to know, whatever method you settle upon. Memory and experience are much more interesting than charts and numbers.
     
  12. Alan W

    Alan W Subscriber

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    I've got a pentax me super that has had a yellow filter on it for years,I've got a pentax 645 that I regularly use a red filter on and both in camera meters have always been spot on in metering for filter factor.I use an rz67 with a minolta iiif light meter and any time I use a filter on this camera I just hold the filter over the meter and take the reading,it always comes out fine,maybe I've got lower standards than some but I've always been happy to let the meter do any adjusting when it comes to filters.
     
  13. George Collier

    George Collier Member

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    I've always looked at filter factors like this: The factor is an adjustment to account for the neutral density of the filter. The filter is designed to hold back light in every color other than it's own (some filters being "narrow band", which are more discrete, and some "broad band", which are less so, allowing more passage of other colors). So the filter factor for a red filter is used to bring the reds back to the same exposure level as before the filter was applied. Everything else will expose less than without the filter, which is the desired result. Does this make sense?
    In any case, I've never metered through the filter, for the reasons of spectral sensitivity differences (film to meter) stated by others here.
    I think also, your particular film, filters, equipment, processing, etc. also probably require your own tweaking and experiencial judgment over time.
     
  14. Leigh B

    Leigh B Member

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    I meter bare-back, then apply the filter factor to the reading,

    I may fudge the factor a little bit depending on the scene and whether I want to emphasize or attenuate specific areas.

    - Leigh
     
  15. Graham_Martin

    Graham_Martin Member

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    Thanks for all the advice. Sounds like I probably need to try both methods and then see what works best for me.