I've converted several, all of the meter sensors are tremendously more sensitive to long wave lengths the the shorter ones. Virtually all meters have IR cutting filters built in. I would suggest that you use the meters I have used for this such as the Luna Pro, you can buy them used pretty inexpensively. Open the meter up, you'll find a small glass filter that has a greenish/blue cast. First clean it! Next get an 87 or 88 gel filter, cut it the same size as the glass filter and insert it, now close the case. Now you will know what the approximate exposure in a daylight situation, so set up the ASA/ISO so that the indicated exposure is the same as the expected exposure. Now it is just a matter of fine tuning the meter according to the IR exposure. This will work for daylight, flash (yes there is a great deal of IR in electronic flash), tungsten, or whatever. If you convert a DSLR to IR it will work for that as well.
I suppose that works with a Luna Pro-F as well?
I simply use my pentax digital spotmeter. I set the film speed to asa 12. If there is blue sky I meter that with my IR filter over the front of my light meter. That is usually my darkest shadow. I check other shadows just to make sure. I place my lowest reading right between zone 3 and 4 and fire away. Hasn't failed me yet.
ETA: I am using Efke IR820 and a Hoya R72 filter.
I want to try SFX200 for pictorial landscapes and want a subtle effect so I'll probably be using a #29 Wratten filter.
Will the meter behave differently if I hold the filter in front of the meter rather than install a cut piece of filter at the sensor?
If you use a 25, then you may not get anything. If you use a 29, you might see a bit with deciduous foliage. One time I was out with Konica IR (similar to SFX 200 and Efke), in the deep shade under pines or similar. I thought that there wasn't hardly any IR around. Boy, was I absolutely wrong. The first exposure and +/- brackets were good, and the rest just turned the film oh-so-overexposed.
With IR, you just take your chances.
Oh, yeah, halation: you won't see it. Kodak film did not have an antihalation layer. The only film you'll get with this is the Adox (Efke) "Aura" IR film.
"It's the way to educate your eyes. Stare. Pry, listen, eavesdrop. Die knowing something. You are not here long." - Walker Evans
Does anyone make a narrow band IR pass filter... something like 600-700 nanometers? Or maybe I can combine a Wratten #70 filter with an IR cut-off filter at 700 nano or so? If so then maybe I could take separate spot readings of visible and IR light so I can combine the two for more predictable results with SFX.
And as I said, you need not worry that much about exposure as long as you stick to SFX. The IR band provided by SFX can be treated as a simple matter of object colour (which you generally don't explicitly adjust your exposure for when using panchromatic film) - in that near-visible range the IR intensity of daylight and incandescent lighting will be in a fairly constant proportion to the visible band.
Believe it or not but my Pentax 67II meters Rollie 400 IR film with Cokin 007 IR filter attached perfectly.