Filter factor

[BMbikerider]

I have just found my old Cokin IR filter with a gel type filter that I last used eons ago. It is one of the opaque type and I cannot remember what filter factor I used when it was last used. I have one cassette of Ilford SFX in the fridge about a month out of date and a few rolls of Rollie 400 IR which are about a year out of date so I would like to use them before they get any older.

I seem to remember I gave it 4 extra stops than the meter suggested is that about right?

 

[markbarendt]

http://en.wikipedia.org/wiki/Filter_factor

 

[MartinP]

For IR it isn't quite that simple as there may be more or less IR radiation, independent of what your visible-light meter is telling you. There should be guidelines with the film I suppose? In any event, make brackets of a couple of stops.

 

[Maris]

For Ilford SFX200 behind a Cokin IR filter I just set EI=6 on my spotmeter, measure the scene directly, transfer the settings to the camera and shoot. I get a high proportion of usable exposures and a few surprises. Infrared is, after all, a bit of a visual lottery.

 

[Denverdad]

If it is a Cokin 007 filter, according to my notes its spectral response should be similar to a Wratten 89B, Hoya R-72 or a B+W 092. As such any recommendations you read for those filters should be close. I can't tell you how to expose using SFX200 specifically, as I only use Efke IR820 film. But the above filter equivalences should be good for making cross-comparisons if you happen to find recommendations for using them with SFX200.



Jeff