Ilford SFX 200 'Near Infrared'

[robertojoven]

I bought a roll of this to use on an abandoned nazi commune up in the hills of LA and had a few questions...

1. I have a red filter for my LF lenses (Hoya 25A) but it is too large for my standard 35mm primes. Will holding it over the lens work well enough or will the focus be skewed?
2. I know that some lenses have an infrared 'setting' on the focusing wheel on the lens to indicate the proper focus. Mine does not. How do I go about achieving correct focus?
3. Should I use TTL metering or my incident meter? What exposure compensation is needed?

 

[Garbz]

1. A 25A filter won't skew your focus at all. IR filters will skew the focus. Holding or not holding makes no difference to this. But in either case unless you want to drive yourself nuts or scratch your filter, just hit up ebay for a stepup ring. I bought a 52mm to 62mm stepup ring of ebay for EXACTLY the same situation for $2.

2. See above. Infrared light refracts at different angles than the visible. The 25A filter however lets through a lot of visible light. Thus there shouldn't be any focus adjustment needed. Do you have autofocus? AF mechanisms work on greyscale light with no low pass filter over their sensor. i.e. they work with infrared light just as well if not better than with visible light. Even with my D200 I compose the shot, put on my Hoya R72 (completely opaque IR filter), and then let the camera autofocus.

3. Read the manual. Ok that's rude, but true. Lots of people don't realise just how much info is in film datasheets, if they know it exists at all. http://www.ilfordphoto.com/Webfiles/2007651134552223.pdf
The datasheet for the SFX200 recommends a filter factor of 1.5 stops for the 25A. This means that for your standard image without filter, what you meter, +1.5EV is what you want to set your camera at. I.e. your camera sees your scene as 1/100th with TTL meter then set it to 1/35th or so in manual, and THEN put the filter on.

That said because the 25A is a relatively light red you can probably meter straight through the filter, maybe under exposing by 1/3rds or 2/3rds of a stop. All I can recommend is bracket out the wazoo. When I shoot IR film I typically shoot 3 frames at +/-1.5EV. The middle frame taking into account the filter factor. My first roll of Kodak HIE I think I got 3 usable pictures.

i.e. for the 25A if my camera said 1/150th I'd shoot at: 1/20th 1/50th and 1/150th. Except my filter is like an 89B so I wouldn't be anywhere near 1/150th