Rollei Infrared film/filter difficulties.

I'll post this under Pinhole stuff, since in this specific instance I am using the Rollei IR film in one of my pinhole cameras.

I will first state that I have been using infrared and red-extended emulsions since the early 1980s, when I was shooting the Kodak HIE 35mm (what a wonderful film that was!), so I pretty much know what's what when it comes to using filters with these films, etc. However, I got an unpleasant surprise yesterday when I shot a roll of Rollei IR 120 in one of my pinhole cameras, with a Lee Polyester 87 filter: I got no exposure on the roll whatsoever. My understanding is that the Rollei emulsion is sensitive to 820nm, and the Lee 87 filter states right on it that its begins transmission at 730nm and further. With that combination, I assumed there would be sufficient overlap to get reasonable exposures, but I got nada! (It wasn't my processing that went wrong; the rebate numbers developed as expected) I metered the scenes at 3ASA and then bracketed up to 2 stops over (sunlight scenes, exposed up to 18 minutes), so there ought to have been some exposure occur.

If I have missed or misinterpreted something, its not obvious to me what that is. If you have experience in this area, can you please advise me? I suspect that although the film + filter specs suggest compatibility, they aren't really.

Thanks,
Paul

Hmmm! In some stuff I've accumulated off the web, the #87 filter is described as having a 770nm cutoff. Now I suppose it could "begin transmission at 730" but maybe the question could be how much -- dunno. At any rate, I have shot some of the Rollei IR (with lens) with a "760nm" filter and it required around six stops more exposure than with a 720 to get something decent.

I assume you have frame info in the rebate and didn't put the fixer in first!

There is also the usual issue of some scenes, particularly in winter sun, not being all that rich in IR. I agree though you'd think there would be something - a reflection of a piece of chrome or an icicle or .... Maybe a six or seven stop bracket would be worthy (although that stuff is expensive to experiment with.

EDIT: I am reminded of the recommendation to shoot one frame at 400 without a filter to get a cross check on processing (assuming roll film).

DWThomas said:

Hmmm! In some stuff I've accumulated off the web, the #87 filter is described as having a 770nm cutoff. Now I suppose it could "begin transmission at 730" but maybe the question could be how much -- dunno. At any rate, I have shot some of the Rollei IR (with lens) with a "760nm" filter and it required around six stops more exposure than with a 720 to get something decent.

I assume you have frame info in the rebate and didn't put the fixer in first!

There is also the usual issue of some scenes, particularly in winter sun, not being all that rich in IR. I agree though you'd think there would be something - a reflection of a piece of chrome or an icicle or .... Maybe a six or seven stop bracket would be worthy (although that stuff is expensive to experiment with.

EDIT: I am reminded of the recommendation to shoot one frame at 400 without a filter to get a cross check on processing (assuming roll film).

Click to expand...

Thanks Dave,
I'm leaning towards the notion that the filter doesn't transmit very well until you get to the 770nm range (the packaging it came in states it begins at 730nm), but given that the Rollei emulsion states in the specs that it is sensitive up to 820nm, there should be sufficient overlap to get some exposure. I metered at 3 ASA, which is seven stops over box speed. I've used this emulsion in varoius cameras with the Hoya R72 filter, which isn't THAT different and gotten very good exposures at 5 ASA in January conditions (See: (there was a url link here which no longer exists) ).

And yes - as I mentioned in the original statement - the rebate numbers developed as expected.

DWThomas said:

Hmmm! In some stuff I've accumulated off the web, the #87 filter is described as having a 770nm cutoff. Now I suppose it could "begin transmission at 730" but maybe the question could be how much -- dunno. At any rate, I have shot some of the Rollei IR (with lens) with a "760nm" filter and it required around six stops more exposure than with a 720 to get something decent. ...

Click to expand...

Dave this has been exactly my experience with this film as well. Paul I've been using a 720 filter with my pinhole camera at what I call -1 iso. That's one stop below the lowest setting on my Luna Pro of .8 iso. For the 760 filter I had to go to -5 iso. The Rollei spec sheet does show this film's sensitivity out to 820nm but if you look at the curve it plummets after 700nm, so the speed in this range is quite low.

Yes, the Rollei IR data sheet says "up to 820" but the sensitivity curve shows it on its way downward in the 700 to 720 range. (As an old electronics-oriented type I think "3db point"). At 820 it's near the bottom of the graph.

Now the old EFKE "IR820," as the name suggests, that cutoff was around 820. Using it, I found I only needed about one stop additional with a 760 filter over what I used with a 720.

The Rollei was way different -- as in lower sensitivity out there.