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cshimokita
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Extended Red Sensitivity Film (Repost from Sep-2014)

Infrared film has always been an interest...  In Nov-2007 KODAK announced that it would discontinue HIE IR 35 mm film due low market demand.  Efke 820 is also gone... so in 2014 I tried Ilford SFX 200, a B&W film that has extended red sensitivity (up to 740nm) together with a R72 Infrared Filter.  The camera was the Nikon F3P with the AIS 50mm f/1.2...

Exposure...  The Ilford SFX 200 data sheet recommends shooting in bright sunshine in order to obtain the best results.  According to the filter mfg "the filter factor for the R72 is highly variable and depends largely on the ISO sensitivity in use and lighting conditions".  From different articles on the internet I found that a good baseline for my exposure tests would be to meter the film/filter combination at ISO 6.  ISO 200 film metered at ISO 6 is a 5 step difference, a baseline Filter Factor of 32.

The general consensus is to shoot a test roll from a baseline and bracket plus/minus two steps, which at three shots per composition would give me 12 unique lighting condition tests in a roll of 36 images...  I did plus/minus one step.

According to the filter maker, "lighting conditions" have an impact on the exposure... depending on what you are looking for as a final image... and true enough my tests when using SFX 200 and the R72 filter showed the following:

• in shaded sunny conditions meter at ISO 3 i.e. 6 steps / FFactor of 64
• in bright direct sunshine meter at ISO 12 i.e. 4 steps / FFactor of 16

... there was some variance, so it's only a guideline and bracketing is recommended.

A word about focusing...  When working in the IR range you need to focus slightly different than you do with visible light... on older lenses you might see a little dot on the distance scale... the idea is to focus using visible light and then adjust according to the position of the dot... I was shooting at f/5.6 or f/8 with a 50mm lens.  It's impossible to focus a SLR with the R72 attached... so the process was to pre-focus / compose before mounting the filter... in bright sunshine the exposure times were in the range of 1/15 or 1/8 second...a tripod is handy.

Development... Ilford SFX 200 is a standard B&W film (it is not chromogenic, C-41) and requires no special handling during development.

If I was spending a month or so in a remote location I would most likely shoot a couple of rolls...

First or second look, hope you don't mind the repost...
Casey