Allen, this may not be helpful to you but it will hopefully be helpful to someone later on —*and it's apropos to your post. My apologies if this is interpreted as hijacking!
Originally Posted by AllenBaxter
I was looking for information about IR filters a few months back. I bought an Opteka R72 (inexpensive Hoya knockoff) from 47th Street Photo on evilpay. It was about $22 shipped, new. It claims to block everything below 720nm. After I ordered it, I found this post: http://www.apug.org/forums/archive/i...p/t-82599.html
... and not much else in the way of user reviews. The person in that post claimed that the Opteka R72 was not a true 720, but rather it cutoff much higher. His efforts with the Opteka R72 and Rollei IR, failed. Blank negatives. He concluded that it was because the Opteka's IR cutoff lay beyond the sensitivity of the Rollei (820?).
I had already bought the Opteka filter (55mm) so I wasn't really gambling. I gave the filter a go last weekend and just processed the negs. They came out fine, about a stop underexposed.
I was using Ilford SFX200 — which, as you probably know, has much lower sensitivity to IR than does the Rollei. It cuts off around 740nm. For each frame, I metered a middle gray at 12 iso, focused with the filter off, re-attached the filter, adjusted the focus for IR and released the shutter. I was using a tripod in full spring sun right around the magic hour in the evening.
ISO 12 is four stops under box speed of 200. I also shot a few frames without the filter, metering for ISO 200, to use as a benchmark.
My impression is that I should have metered for ISO 6 with the filter, and ISO 320 without the filter. The benchmarks look dense. Souped in Rodinal 1:100 for 60 minutes.
I haven't made prints yet but the negatives look sharp. I am still sans-scanner / full analog ... so everyone reading this will just have to imagine beautiful, dreamlike infrared landscapes — because I have no way to post them.
Last edited by pstake; 03-31-2012 at 06:35 PM. Click to view previous post history.