Questions about filters for SFX-200

[Andrew O'Neill]

In a test mentioned upthread I used EI 6 with an 89B. I suspect with an R72 which has slightly higher cutoff (best I can tell), another stop would be a good idea. I generally do a bunch of bracketing with the view that this IR stuff falls into the "grand experiment" category. It's also good advice to shoot one frame unfiltered at nominal ISO on a first effort to verify the processing, although that is probably more important with film further into the IR spectrum.

I shoot at EI 6 with the R72, on a bright, sunny summer day.

 

[pbromaghin]

It's also good advice to shoot one frame unfiltered at nominal ISO on a first effort to verify the processing, although that is probably more important with film further into the IR spectrum.

I don't understand this statement. But I want to know what you are saying because you have really explored this and know what you are talking about. How would this be a benefit?

 

[pbromaghin]

I shoot at EI 6 with the R72, on a bright, sunny summer day.

So Ilford recommendation + 1. Am I right? Oh shoot. Maybe not.

 

[pbromaghin]

The filter arrived, but it is not what I expected. In the package it's BLUE! However, it appears that it is reflecting the blue and green light, instead of absorbing it. Not like most filters that I have ever seen. When I hold it up to my eye and look through it at a light source, it looks red. From all other angles, it is blue or green...

Is this normal?

 

[MattKing]

I don't understand this statement. But I want to know what you are saying because you have really explored this and know what you are talking about. How would this be a benefit?

Your meter isn't sensitive to the near IR and portion of the spectrum that the film's sensitivity barely extends into. The film and meter are sensitive to the visual spectrum, but you want to block most of that out with the filter, so that the near IR and IR are revealed. Sometimes, there is so little IR in a scene that when you take the photo with the filter in place, you are left with an almost blank negative. A test shot without the filter and using the normal exposure for visible light and an ISO of 200 - the native ISO of the film - will yield a perfectly usable, normal negative. That will serve as an excellent test of your developing choices for the film.

So Ilford recommendation + 1. Am I right? Oh shoot. Maybe not.

All the suggestions for an EI have to be based on practical experience, because none of us have a meter that actually measures the IR. What we end up doing is measuring how much visible light there is with the meter, and estimating how much near IR and IR is accompanying that measured visible light. That estimate will tend to vary because of differences in location, season, foliage, time of day, etc., etc. - all the factors that no one has ever been able to provide objective and accurate measures for. The variation in guesses may very well be due to the variation in location and experiences of those who make those guesses.

The filter arrived, but it is not what I expected. In the package it's BLUE! However, it appears that it is reflecting the blue and green light, instead of absorbing it. Not like most filters that I have ever seen. When I hold it up to my eye and look through it at a light source, it looks red. From all other angles, it is blue or green...

Is this normal?

Yes. You should barely be able to see light through it.

Have fun.

 

[DWThomas]

I don't understand this statement. But I want to know what you are saying because you have really explored this and know what you are talking about. How would this be a benefit?

Matt has provided an answer far more eloquent than I was likely to come up with! Yes, if you've not tried the film before, one shot without the filter, metered for the nominal ISO, provides a base for your processing. It might be less critical with SFX, but with something like the old EFKE stuff, missed estimates with the IR filter might give an almost blank roll, so having one "normal" shot lets one assess whether that purple D-76 died or whatever.

 

[pbromaghin]

Thanks to all of you! A guy can't help but succeed with all this expert help.