Infrared Film Exposure Times

[thomascanty]

Does anyone here have experience with film IR photography? I'm trying to figure out what kind of exposure times I should be using with Kodak High Speed IR film and a Hoya R72 filter. The spec sheet with the film gives some sample exposure times (ie: 1/60 at f/8 for nearby sunlit scenes), but it says that is when using a Kodak Wratten gel filter no. 25. Can I expect to use the same or similar settings with a Hoya R72 filter?

Thanks for any help.

[Longwatcher]

This probably isn't any help, but just in case nobody else has the info.
I recommend "wasting" a roll of film and just try different settings starting with the stated set and working to longer shutter or wider aperture in 2 or 3 full stop increments. After getting it back, then you know which is best setting for that shooting situation.

Reason:
A Wratten 25 has a cut off of 600nm or somewhere in the red-orange? region
A Hoya R72 has a cut off of 720nm or in the far red, near-ir boundary region. Thus you will most likely need more light.

Just my opinion,

[sdommin]

I used to shoot lots of HIE back in the old days. The R72 filter is different from the Red #25, so I wouldn't use the same settings. I always used a red #25 filter - the main advantage being that you could see through the filter to frame your shot. Exposure is a "hit or miss" kind of thing because the amount of infrared light varies greatly from day to day, even from hour to hour. My advice: experiment and BRACKET greatly. Also, when they say "load the camera in complete darkness", they mean it!

I used to use a hand-held light meter and I got to where I could get fairly consistent results (keeping in mind that my developing procedures and techniques were standardized: 11 minutes in straight D76 at 68 deg.). I would put the meter on ASA25 and take the reading off of the sunlit foliage (if it was in the scene) to get my exposure. Again, I only used the red #25 filter so I can't speak for the R72.

http://home.att.net/~sdommin/ir_falls.jpg

[Jon]

The recommendation for HIE was always bracket, bracket, and then bracket some more. The R72 cuts out 'most all the visible spectrum so there's not much for your internal meter to rely on. It's more like the Kodak Wratten 89 or so. Start with an external meter and a filter factor of 4 stops or so and go from there.

[thomascanty]

Thanks for the help, everyone. I did a lot of searching yesterday and also talked with Dan Heller, so I got a few ideas. Most other people were telling me to use a #25 filter, so I picked one of those up on my way out to Laughlin this morning, but I'd like to give the R72 a try as well. I wasn't finding much help on using the R72, but most people on photo.net seemed to agree that setting the camera to ISO400 and letting the camera do the metering with a #25 filter was the best way to go, provided I bracket (of course). I have a lot of experimenting to do. I'm beginning to wish I'd brought more than one roll of film, though. Does anyone know of a camera store in Laughlin, in case I run out of film? :lol:

As for loading the camera in complete darkness, I was practicing that the other day. My hotel bathroom is pretty dark with the door closed, so I'll probably do it in there. I also picked up a changing bag this morning for good measure.

Thanks again!