Reciprocity Effects on APX25

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Does anyone know the reciprocity effects on APX 25 and how to compensate for them in development? I have a roll with exposure times of 15 to 60 seconds.

I'm guessing reduce development by 20% or so but I can't seem to find the data sheet for even APX 100 or 400 anywhere on the Agfa Web site.

Thanks in advance....

-- David Parmet (david@parmet.net), January 03, 2002

Answers

Agfa does not recommend to make a correction in development. Agfa recommends to give 1.5 to 2 stops extra if your normal exposure time would be 10 to 100 seconds. Reciprocity law failure is not determined by the shutter speed, but instead by the light intensity the film receives. So what Agfa recommends is not a definite one, depending on your normal rating of the film, etc.

For long exposure on this film (and TMX), I liked to use dilute Microphen.

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), January 03, 2002.


You can't properly compensate for low-light reciprocity failure at the development stage. Reciprocity failure causes underexposure, coupled with an increase in contrast. Pulling the developer will decrease the contrast, but it'll also lose you a lot of shadow detail.
The best you can do, post-exposure, is to give slightly extended development using a compensating development technique, like two-bath, stand, or highly diluted development; or a slightly curtailed normal development, followed by a few minutes in a plain water bath without agitation. The latter technique allows the shadow and mid-tones to 'catch up' on the highlight density, taming the contrast without losing too much film speed.

-- Pete Andrews (p.l.andrews@bham.ac.uk), January 04, 2002.

Thanks for your advice, both of you.

I exposed the film at my normal EI of 12. My shutter speeds were either 4 or 8 seconds at f16 so I gave each shot a 4, 8 and 16 second exposure. One other one was at 16 seconds so I gave that 16, 32 and 60 seconds.

Normally I'd develop APX25 in Rodinal 1:100 for 7 minutes. I'm thinking now I may dilute the Rodinal at 1:200 with my normal amount of stock solution and give it 15 minutes or longer with reduced aggitation so the highlights aren't blown out.

-- David Parmet (david@parmet.net), January 04, 2002.


Reciprocity failure tend to increase contrast of shadow zones selectively. This is in contrast to sunny day's photo, where you determine exposure for shadow zones and you'll get excessive contrast in highlights. For this reason, I find Microphen very effective for nightscape where I often expose for dozens of minutes on TMX. I don't use APX25 for nightscape but as a rescue I see why not Microphen or XTOL doesn't work the same way. I'd use 1+2 or 1+3.

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), January 04, 2002.

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