Using box speed, taking a light reading and adjusting for the filter factor is more accurate that arbitrarily setting an effective ISO. Filter factors are supplied by the manufacturer, who actually know what they are doing, not like the random number pulled out of the air, guessing, without any knowledge.
R23 filter factor 2
R25 filter factor 3
R29 filter factor 4
720 aka 72R filter factor 5
filter factor =5 (25 A = 8 filter factor) or 5 stops = 32 filter factor? What I used is effectively to 6 or 7. I am not finding R72 filter factors on Hoya or any websites. I found one unofficial listing of filter factor=20 to 40 .
I did not make this up, but checked to see what worked with other photographers on Photrio and Flickr, and back calculated filter factors as a check. It made sense that the filter factor for R72 should be higher than 25A, I think. I just found it easier to use effective ISO around 6-16 with the filter on. You end up in a very similar place.
Look at my post: R25 [25A] has a factor of 3 [23 = 8 times the exposure time], 720 [72R] has a factor of 5 [25 = 32 times the exposure time]. Mathematics shows that 5 is greater than 3. I have found the filter factor for the 720 listed as 6 but that was a little too high sometimes from my work with it.
https://en.wikipedia.org/wiki/Wratten_number
I am not finding R72 filter factors on Hoya or any websites. I found one unofficial listing of filter factor=20 to 40 .
I loved HIE, but after it disappeared I tried several other Infrared films. I like the Rollei IR 400 the best and I use the R25, R29 and 720 filters the best with it. The R23 is a little too weak for IR film, but it darkens the sky without turning it black that the R25 for panchromatic films and is stronger than the Orange filters.
An image from my second time shooting IR. Bronica RF645, 65mm @ f22 on Rollei Infrared 400.
Nice
Indeed, but what is going on to the sky?
Indeed, but what is going on to the sky?
Uncertain, I think my film lab may have done something wrong in the development process. Other shots had random black spots scattered about.
I agree. The moisture of the scene cannot be the reason in my opinion. Have you asked the lab already?
Recently picked up a Chroma Snapshot 4x5. Decided to test it with a sheet of Rollei IR 400.
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