Thanks Lomography answer & RF correction reply

I have seen a number of b/w films that have a base 10
log response to long exposures:

0 stop at 1 second; logten of 1 = 0
1 stop at 10 seconds; logten of 10 = 1
2 stops at 100 seconds; logten of 100 = 2

Fuji Superia (cheapo 35 mm 4-packs 200 ISO) is 1/3
stop for 4 seconds, 2/3 stop for 16 seconds, 1 stop
for 64 seconds. I see a pattern here too; looks like
0.5 scaling factor from above, with roundoff to
fractional stops rather than 0.3, 0.6, 0.9 that come
from log of 4, 16, 64).

Interestingly, some charts say NO RF correction for
Kodak C41 chromogenic B/W...hmmm.

If you have no RF correction info at all for a given
film, other than the C41 example above, I'd estimate
adding a number of stops equal to somewhere between
the 1/2 and 1 times the log-base10 of an exposure
greater than 1 second.

I've promised to share a spreadsheet (open source? for
public enhancement) that pre-charts long exposures
based on EV and Zone placement. It includes a RF
correction scaled to a particular film based on one
datum pair (correction at given exposure time) entered
by the user. I don't know how ideal it is, or how
precise it really needs to be for long exposures.

I keep getting distracted and busy, but I'll work on
it.

I may be making it much more complicated than
necessary, but that's my nature.

Murray
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Received on Tue Mar 22 15:14:35 2005