Infrared Film Exposure Question
I am new to Infrared film photography. I plan on using Rollei IR 400 film and the Hoya R72 filter. My question is that I have read several threads regarding exposure and have gleemed the following: shoot at ISO 25, at approximately 1/2 sec @ f16. My confusion is how do you meter? Do you make your TTL measurement and adjustments before putting the filter on the lens and adjusting 6 - 8 stops or do you measure TTL with filter on?
Just my two cents, from what I learned from this forum, the meter can't read infrared light so if you put the filter on first and then measure TTL, it will give you an error instead. There are thing I've learned for Infrared film is: bracket, bracket, bracket, bracket.
I've got a couple of shots here in my APUG gallery that were shot with Rollei IR 400 film and an R72 filter. Here is an example:
In my case, I used a Mamiya TLR and a hand meter. One of my successes was metered at EI 3, while another was metered at EI 12.
It is of course difficult to determine how much IR is included in the light being measured by the meter, but it definitely does change as the light changes, so a suggested standard exposure isn't likely to work consistently - bracket instead.
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I never bracket IR film except to set up this procedure.
I use a RF camera, and set the camera behind the lens meter to 1000 for 400 speed and meter thru the B&W 092 at a subject that needs to be rendered middle grey on print. Or meter deciduous trees or nice green grass and open one stop.
This works with Leica M and R cameras and the clip on meters. Cameras have SBC cells and clip on has CDS. Both work the same. Any meter made since 1960 has one of these two cell types.
Multiply your film speed by 2.5 and run the test. If your 072 differs by a little, the meter will compensate.
Bracketing this expensive film is a waste of $$$.
My sunny day light exposures were 1/250 at 6.3. Meter or not, this worked every time and I never missed exposure.
I may be wrong, not having used IR film for very many years but I recall that a focusing correction was needed. I remember lenses having an indicator. You would focus normally and then move the focus to a line or "r" on the lens.
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What IR film was this? This speed at this aperture seems very fast compared to what most say is the kind of exposures necessary. Handholding would seem to be a problem for most IR users but clearly not at this speed.
Originally Posted by Ronald Moravec
I have tried metering through the lens with the Hoya R72 filter and the meter does not appear to pick up any light. The filter is really opaque. How does the Hoya R72 filter differ from the Red 25A filter?
Since I am new to film photography I am not sure fully understand your response. Are you saying to multiple the Rollei film speed of 400 by 2.5 and set the ISO to 1000 and then meter through the lens with the Hoya R72 filter in place? Thanks
According to a Hoya brochure, a 25A filter passes light of wavelengths above about 600 nM which is well into the visible range. The R72 cuts off below 720 nM which is nearly out of the visible range. I have never shot IR film in a camera with a built in meter, so I have no experience to go on there. It seems possible to me that even if a light meter sensor has IR sensitivity, the maker might put some filtration over it to reduce sensitivity outside the visible range. (That's done with the sensors in d!git@l cameras.)
Originally Posted by AllenBaxter
Based on my limited experience, I think Ron's exposure sounds a bit short, but in spite of the anti-bracket comments, I think a bit of it isn't a bad idea until you establish some sort of base line.
It seems like there's some variation in the sensitivity of different meters to IR. I've had some luck metering through an R72, but for some people it's been a complete failure; I don't know if the difference is down to different built-in filtration, or different lighting conditions, or just blind luck...
Even guidelines based on assuming a certain EI are variable, because the ratio of visible light to IR light varies. You know how sunsets look red---that's because red light propagates better than other colors through the atmosphere and haze and dust, and the same goes for infrared. As a result, at sunrise or sunset, the EI of an IR film is *higher* than it is at noon! (There's less total light, but what light there is skews to the red/infrared---thus IR film through a filter actually sees more light at those times than the amount of visible light would suggest.)
While metering through the filter might work in a pinch, on the whole I wouldn't count on it. I tend to think it's always best to shoot IR film with a handheld meter---and then the hard part is choosing what speed (EI) to set the meter to. The speed that's worked for other people is a starting point, but for your particular conditions it may or may not be ideal. I'd say, take someone else's suggested EI as a start, shoot an experimental roll with some bracketing, and evaluate the results to figure out what works for you.
A compensating developer is also your friend. I've become very fond of IR films in Diafine, which seems to "level out" the exposure variability quite a bit.
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