IR metering

[pbromaghin]

I've been playing now and then with Infrared film. In fact, my first print in my home darkroom is from infrared film in medium format and I am considering the purchase of Rollei IR400 in 4x5. I just meter the scene with an incident meter and add 5 stops. Analog Andy uses a spot meter and the zone system with IR. Being invisible to the human eye, how is that possible? Or does his meter "see" infrared? Maybe Andy could weigh in...

 

[MattKing]

None of the meters we use reliably meter IR light.
However, the level of IR light tends to correlate with the amount of visible light, as long as we take into account a number of other factors, such as season, status of foliage, temperature, cloud cover and others.
Our experience with photographing with IR materials leads to knowledge about how much and under what circumstances those IR light levels correlate with the visible light levels we can measure with our meters.
So we measure the visible light, and from that make educated guesses about how much IR light is around as well.
Then we use a filter that blocks out all or most of the visible light, while letting the IR light through.

 

[jvo]

None of the meters we use reliably meter IR light.
However, the level of IR light tends to correlate with the amount of visible light, as long as we take into account a number of other factors, such as season, status of foliage, temperature, cloud cover and others.
Our experience with photographing with IR materials leads to knowledge about how much and under what circumstances those IR light levels correlate with the visible light levels we can measure with our meters.
So we measure the visible light, and from that make educated guesses about how much IR light is around as well.
Then we use a filter that blocks out all or most of the visible light, while letting the IR light through.

What a marvelous, concise and clear definition of IR photography!

My mind immediately went to the rabbit hole of spectrum, frequencies and temperatures - and really confused things

 

[xkaes]

One big factor is the "factor" of the filter you are using. Not all IR users use the same filter, and some IR users use multiple IR filters for different effects. I won't mention all the ones I use.

If you are only using one "IR" filter that makes it easy to run some simple tests for the best filter "factor".

The filter factor will always remain the same, but the exposure will vary depending on how much IR light there is in the scene -- as Matt has mentioned.

 

[Sirius Glass]

None of the light meters see IR properly, however for many years I use the light meter set at the box speed and then open up the iris the appropriate number of f/stops or increase the exposure time accordingly for the filter factor.

 

[Andrew O'Neill]

My metres don't see IR. I've used a regular spot metre with Kodak HIE quite successfully. With current IR films like Rollei IR which isn't as sensitive to IR, regular spot metres are fine. I certainly do not take readings off of things that are very IR reflective, like foliage, though. I always expose for the shadows (very little IR there). When it's difficult to metre a shadow area easily, my little grey card comes in handy! I use two brands of IR filters. The cheap Zomei 720, and the more expensive Urth 720. Both have the same factor of 32x (5 stops). When using Rollei with no IR filter, I shoot it at EI 200. With the filter, I'm down to EI 6.

 

[pbromaghin]

It seems this will require a lot of experimenting with different exposures and under different conditions. I went for a late morning walk today to a nearby park with some pretty decent subjects and looked at them with all of the comments in mind. Tomorrow I'll go back and burn up a roll on 6x9, experimenting with different adjustments. It will be pretty much all full sun. Then I'll have to pick up some more film. Oh boy, lot's of fun coming up!

For now, it will all be incident metering as I don't think I'm quite ready to take on the Zone System.

 

[Nicholas Lindan]

Silicon photodiodes, used in all modern meters, are quite sensitive to NIR. They often have a pale blue filter in front of them to cut their IR sensitivity but it is not completely effective.

See if you can meter through an IR720 filter. If the meter responds then you should be able to calibrate the meter to the proper exposure for the film. Bracket the film exposure, pick the best one, and using a reflected light meter find the ASA that gives the reading for the 'proper' exposure. However, there is not really any need to meter through an IR filter.

The ratio of visible to IR light will hold rather constant and so a regular light light meter with a simple correction will work. I have found that bog-standard metering with a 6-stop correction gives acceptable IR negatives when shooting Rollei IR with an IR720 filter. Open up an additional 1-2 stops for subjects in shade.

 

[Andrew O'Neill]

It seems this will require a lot of experimenting with different exposures and under different conditions. I went for a late morning walk today to a nearby park with some pretty decent subjects and looked at them with all of the comments in mind. Tomorrow I'll go back and burn up a roll on 6x9, experimenting with different adjustments. It will be pretty much all full sun. Then I'll have to pick up some more film. Oh boy, lot's of fun coming up!

For now, it will all be incident metering as I don't think I'm quite ready to take on the Zone System.

I like to look at the subject with the IR filter over one eye. Once your eye adjusts (pretty quick), if there is a lot of IR reflection in the scene, you will see it and decide whether or not the subject under those conditions, is worth it.

 

[pbromaghin]

I like to look at the subject with the IR filter over one eye. Once your eye adjusts (pretty quick), if there is a lot of IR reflection in the scene, you will see it and decide whether or not the subject under those conditions, is worth it.

Great tip. I'll try it tomorrow.