Here's a synopsis of a recent experience in shooting involving several hundred frames of Efke IR 820 and Efke IR 820 Aura in 4x5 and 120 roll film formats. My subject matter was mountain landscapes in all weathers.
The "Aura" feature does not do much on big film as the image "halation" or "flare" is quite small. I imagine in the 35mm format where the enlargement ratios are greater the "Aura" would be more prominent. Bunches of green leaves which "glow" in the infrared tend to merge into fuzzy blobs with significant over exposure. This effect is worse with the Aura version of Efke IR 820.
There is a loose (did I say loose?) correlation between conventional meter readings and infrared exposures. My Pentax analog spot meter was set at EI=1.5 for front-lit sunny scenes, EI=0.75 for sunny day subjects where shadow detail was important, EI=0.3 for cloudy overcast days. Exposures were through IR680 and IR720 filters. Surprisingly it did not matter which filter was used. The results looked much the same!
The IR680 and IR720 filters, 77mm diameter, came from China via Ebay. They cost about $20 each. It is possible, for me at least, to see through these filters and preview the infrared effect. The filter has to be held close to the eye, extraneous light carefully excluded, and the eye "dark-adapted" for about 30 seconds. I suspect that with the iris of the dark-adapted eye being wide open looking at the sun through an IR transmitting filter would be a very bad thing indeed.
Efke IR 820 film shows significant reciprocity failure but the following corrections are what I use:
1 second metered, give1.5 seconds
2 seconds metered, give 3.0 seconds
4 seconds metered, give 6 seconds
8 seconds metered, give 12 seconds
15 seconds metered, give 30 seconds
30 seconds metered, give 80 seconds
60 seconds metered, give 3 minutes
120 seconds metered, give 6 min 40 sec
240 seconds metered, give 18 minutes
These reciprocity corrections pretty well guarantee you'll get something useable on film but not exactly what you will get. Shooting IR is rolling the optical dice everytime.
Infrared focus shift is real and horrible. Everything I shot with the 360mm lens on my Mamiya RB 67 is out of focus. I suspect I have to rack this lens out about 5mm to compensate the difference between the visible and IR focii. More exact measurements are planned. Wide angle lenses well stopped down yielded sharp images but only because increased depth of focus forgives imprecision.
Some development variations were tried including hot paper strength Dektol! This was supposed to cure the reputation IR negatives have for low contrast. Cure indeed! The resulting super-contrasty negatives still made acceptable (sort of) pictures on grade#0 and grade#1 paper. Optimum development for my film now seems to to be 11 minutes at 20 Celcius in straight replenished Xtol. YMMV, naturally.
In practice Efke IR 820 like other IR films I have tried both disappoints and exhilarates. A lot of subject matter I had high hopes for yielded unremarkable schmutz but some plain things turned to visual magic. That's the deal.