Efke 820IR/ Lee 87c gel

[robertojoven]

I have read a small (but substantially confusing) amount of information regarding infrared photography as it relates to filters and was hoping that someone might be able to offer some clarification.

I purchased a 25 sheet box of Efke 820IR film the other day, as well as a Lee 87c gel. I am still unclear as to a few things:

1. What exposure compensation is needed for this filter? (I have heard/seen numbers ranging from an effective ISO of 1/2 all the way to 6 or 8)
2. What wavelength does the 87c cutoff at?
3. (regarding question #2) Will this give a dramatic IR look, moderate IR effect, or is the filter too opaque?
4. Shooting in southern california deserts in spring on bright sunny days, will there be enough IR light?
5. What sort of development (D76) is preferable?
6. Should I purchase a different filter (I also have a 25a, although I don't think this is deep enough)?

I was planning on doing a test run and bracketing 4 or 5 shots, but I read that the 87c cuts out too much light so I don't want to spend a day shooting only to receive completely black images.

Thanks

 

[maris]

Here my Efke IR820 exposure strategy through a IR720 filter. The Lee 87c is very similar to the IR720 although it has a nominal 730nm cut-off. My light metering is via a Pentax Analog 1 degree spotmeter.

Front lit landscape, typical sunny day: EI = 1.
Subjects in the shade on a sunny day: there is still some IR kicking about but the ratio of IR to visible is lower so I set EI = 0.5 on the meter.
Cloudy day, even light, no hard shadows: there is even less IR for every bit of visible so I set EI = 0.25 on the meter.

Except for infrared bright leaves and brilliant clouds I have a deuce of a time overexposing this film at any remotely reasonable camera settings. If in doubt give more. Still unsure? Give much more! I never bracket exposures with this film. It is too expensive and the concept of "correct exposure" is a bit vague in the wild and woolly world of infra-red photography.