Topic: Using a digicam for exposure examples

[choppert]

Guys,

Probably a simple one.  I want to do a few more long exposures and thought I'd use the digicam to test exposure times.

I exposed at ISO 3,200 for 30 seconds at f4.0 (an EV of -1?)

If I then want to work out the correct exposure (by fiddling with my light meter) for f22 at ISO 400 I think I get to 2 hours - before any reciprocity compensation? I think I also get to 4 minutes at f4.0?

Have I done that right?

Any rules of thumb for film reciprocity failure?  If I were to use my two hour exposure would I need to increase it to four or six hours?

Thanks,


Chops

[Sandeha Lynch]

Every film is different, so this may help, a handy guide in seconds from somewhere in cyberspace.



You'll see that the newer bw emulsions need less extra time than the older classics.  IIRC, some colour negs go way off almost immediately and need filter correction, while (I think) Provia has virtually no rf at all.

[byron]

while (I think) Provia has virtually no rf at all.

That's correct, and it's one of the reasons I shoot provia so much. No reciprocity failure up to 2 minutes, and minimal correction time (1/3 of a stop) after that.

Also, ChopperT, your math seems fine to me!