[DWThomas]

How does the filter type chosen effect the exposure with Efke 820? I have an 850nm filter, should i be using 720? I did get some good results with this filter, just checked the details and the best were 1sec @ f16, though other shots at same exposure were not as good.All were shot within 4 hours on the same day but at different locations and aspects.

Based on my limited experience, the 850nm filter should be OK with the EFKE film - you might need one stop more exposure for the 850 than the 720. If you run the cutoff that high with the Rollei material, you'll be looking at another 5 or 6 stops over the exposure with a 720.