Filter Factors Calculator
Filter Used = 15
Filter Factor = 1.5
F/Stop Change = .58
Nearest 1/2 Stop = 1
Nearest 1/3 Stop = 2
Adjust ISO Method:
ISO Before Filter = 100
ISO After Filter = 67
Calculates the approximate increase in exposure needed when using color contrast or ND filters in B&W photography.
Exposure can increased by using a larger aperture, reducing shutter speed or a combination of the two. Some photographers use 1/2 stop increments while some lenses and meters show 1/3 stop increments. The table linked below might be useful in making aperture (f/stop) changes:
[http://www.fineart-photography.com/stops.gif|Full & Fractional F/Stop Table]
An alternate method is to make the indicated adjustment to the ISO or personal exposure index on a hand-held meter.
-Filter Used: Select among the commonly used filters listed. If the filter used is not on the list select "Enter Factor Manually".
NOTE: Use the filter factor suggested by the manufacturer if it differs from those listed.
-Filter Factor: The filter factor of the selected filter should be shown. Also, the filter factor can be entered manually. If two filters are used multiply their factors and enter the result.
-F/Stop Change: Shows the exact calculated change to two places.
-Nearest 1/2 Stop: Rounds result to nearest 1/2.
-Nearest 1/3 Stop: Rounds result to nearest 1/3.
-ISO Before Filter: The ISO or the photographers personal exposure index.
-ISO After Filter: Filter factor adjusted ISO.
Contributed by Joe M. Miller.
I want to use the Orange #21 filter that has a filter factor of 5. What f/stop would I need to use if the meter reads f/8 @ 1/250 second.
-Filter Used: Orange #21
-Filter Factor: 5
-F/Stop Change: 2.32
-Nearest 1/2: 2&1/2
-Nearest 1/3: 2&1/3
-ISO Before Filter: 100
-ISO After Filter: 20
Changing the aperture only would mean a setting of f/3.5 or f/3.7 @ 1/250 sec. Of course, other options exist such as f/6.7 @ 1/60.
An alternative method would be to change the ISO (ASA on Paleolithic meters) and choose among the indicated f/stop and shutter speed combinations.
Nearest 1/2 Stop
Nearest 1/3 Stop
ISO Before Filter
ISO After Filter