The time in the Massive Dev Chart was tested for us last year by an experienced photographer. As a general rule, you can increase times for Jobo developers by about 15% to get a time for use in a small hand tank. I don't know where your dealer has come up with his time, but based on your information I would try a time of about 12 minutes as a starting point.
You mention that your negs are thin and the film speed is 100 ASA, so you are probably wondering why I am not suggesting a longer time. Well, Infrared film is a strange beast. Firstly, the film speed setting on your camera is more or less irrelevant. Your camera's light meter cannot "see" the infrared end of the wavelength, so no matter what you set as your film speed, this is only relevant to the visible part of the spectrum.
Infrared film requires extensive trial and error to produce the best results. You need to work out exposures based on the amount of sunlight and the tonal range of your subjects in conjuction with a standardized development technique. A lot will also depend on how much of the visible wavelength you choose to filter out. If you are using a red filter, your results and exposures will be quite different to using a weaker/stronger filter, or no filter at all.
My suggestion is to shoot a roll using a shutter speed of 1/60th and an aperture ranging from f5.6 (no sun) to f16 (intense sunlight). You will probably make most of your exposures at f8 or f11. Then develop for 12 minutes with standard agitation and take it from there. Your first roll is a test roll, no matter what.
If you want to develop the roll you have already shot and it looks thin at 14 mins, then you will need to extend the time to get more density.
Film Photography & Darkroom discussion
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