Hi, Im on my way to taking nightphotography and longtime exposures.

>>3103919
what the fuck.

just leave the shutter open until it feels right to close it duh.

File: 8TGbAgbEc.jpg (76KB, 327x327px) Image search: [Google]

76KB, 327x327px

>>3103920
Serious?

>>3103921
works everytime. always get TOP images.

Basically what the other guy said, yeah. Correct exposure with long-exposure photography is a matter of luck and/or skill at bracketing. Or shooting evenly (but dimly) lit subjects, and counting it one-one-thousand, two-one-thousand, and so forth.

As for reciprocity, I'd recommend using either TMAX 400, or Acros. The first doesn't really need compensation until around 20s, and the second can go for minutes uncompensated. I've had very satisfying results from both, but again, with bracketing and patience and luck.

>>3103920
totaly. only guts can tell such things.

>>3103919
Just search for 'reciprocity table [insert film]'
What I found for Portra was this:
y = 0.5167 * ln(x) - 0.2
x = metered exposure time in seconds
y = stops of correction
Since Kodak does not give any information on compensation in their data sheets, I would go with this.

Otherwise you will most likely find some kind of table/diagramm in the datasheet.pdfs, just use your trusted searchengine.

I sometimes use some kind of rule of thumbs like:
5-10s --> +1 or +2s
Around 30s --> 1.5x the time
1min --> double the time
if signifficantly longer than 2min --> triple

But really as >>3103920 said, just test that shit out and if in doubt just shoot twice with different times.

Seems sometimes enormous, but it still is only one stop from 1min to 2min. So bear that in mind and just guess and try out.
With negative films, you really can't fuck up the exposure that much.