 BetterPhoto Member |
filter factors How do I set filter factor compensation on my Sekonic L508? Sekonic gave me 3 answers. If the filter factor is 2 do I set a -2? For two filters having a total filter factor of 3, do I set -3 on the hand-held meter? Thanks, Joe
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Jon Close |
Filters are easier to compensate for when the light loss is given in "stops" (i.e. f-stops) or Exposure Value (EV). When the light loss is expressed instead as a "Filter Factor" it is the value of 2 raised to the power of number of stops lost. So Filter factor 2 = 2^1, equivalent to 1 stop loss; Filter factor 4 = 2^2, equivalent to 2 stop loss; factor 8 is 3 stop loss; etc. Filter factors not a multiple of 2 are more complicated, and are a pain to convert to aperture or shutter speed change. For your example, filter factor 3 is 1.585 stops, but no camera or lens has that fine an adjustment so you use either 1.5 or 1 2/3 as the light loss (i.e. compensate by opening up from f/8 to f/4.8 or f/4.5). You can incorporate exposure compensation for the filter in one of two ways: (1) You can adjust the ISO. If you are shooting ISO 100 speed film but using a filter with factor 3 (1 2/3 stops light loss) you set ISO 32. The L508 allows 2 ISO settings, so you can set ISO-1 to the actual film speed and ISO-2 to the filter-adjusted speed. See page 5 of the user manual for setting the ISO. (2) Set the ISO for the film used, but set the Compensation Function on the meter to -1 for filter factor 2, -1.6 for filter factor 3, etc. See p. 24 of the user manual for setting the Compensation Function. If you don't have a user manual you can download it from Seconic at http://www.sekonic.com/InstrManuals/L-508.pdf
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