Does anyone know exactly how to calculate the exposure time, taking into account reciprocity failure? For example, say I happen to have Ilford Pan F, ISO 50. I determine that my exposure time should be 30 second with out factoring in reciprocity. When I look at the Ilford fact sheet reciprocity chart (here) it shows that I actually need to expose for 150 second.
This seems like it could be fine for the work that I want to do--mainly night scenes near city lights.
If I wanted to do as the OP is suggesting, should I just choose a better film with less (lower?) reciprocity failure, or should is there a way to calculate it?
I have never done an exposure longer than say 2 or 4 seconds, so forgive me for any naivete.
LOL! I deal with people getting hyper-excited about this subject just about every waking hour. And it's not even my staple fodder!
Peter, 35mm will do fine for star trails, and the RB67 will give a much bigger image with more detail; the Speed, ditto. You are spoilt for choices. I'm sure it will occur to you with two tripods and two cameras of different formats to go for it with both of them and come away beaming! And camping — that's the best way to go. Don't be too concerned about overly theoretical distractions like reciprocity failure. Short exposures of static stars are fine; let the film literally go feral over several hours while you pursue other things around camp. I hope you have fun and look forward to learning how you go. After all, Phoenix AZ (in some ways I think it is similar to the parched outback of Australia) is on my itinerary in 2015 (whipping tour of the heavy-hitter national parks). :)
I would say use the Ilford chart as a starting point (it will likely overcompensate) and do a few experiments. Also, luckily, Howard Bond's tests showed that contrast increases with long exposures are not as pronounced as they once might have been, so that's kind of helpful particularly if you overcompensate.
As for using a different film, you will have the same problem, but there are a few generalizations that can be made: 1) tabular grain films such as Ilford Delta and Kodak TMax need less reciprocity compensation than "conventional" films like Pan F+, FP4+, Tri-X, HP5+ etc (although the current versions of these films need less compensation than earlier incarnations). Fuji Acros (another tabular grain film), which was mentioned by Early Riser, is a special case in that it needs virtually no reciprocity compensation for exposures up to two minutes, and much less compensation than other films for exposures longer than that. 2) slower films like Pan F+ will tend to be trickier to use in night/low light photography because these tend to be high contrast shooting situations and slow films like Pan F+ usually have higher contrast and/or a shorter scale than most medium speed or high speed films.
Basically, if you're getting into night shooting, you'll have some experimentation to do, and it will take some practice. Most of my photography is done at night or under other low light indoor/outdoor conditions, often involving very high contrast subjects/lighting (night scenes with light sources like lightbulbs, street lamps etc in the frame). It takes practice, regardless of which film. I've used mostly TMX/TMY and Ilford Delta 100 for this work (I did some extensive testing of Acros but in the end went back to Ilford). These are just my personal preferences though.
One more thing - don't make the mistake of assuming a film needing less reciprocity compensation is a "better" film. It doesn't work that way at all.
My humble offering. I work only with film, both color and B&W. Methods and film tests discussed.
Thank you Michael R, this is very helpful. I usually shoot Delta 100 or 400, so it will be interesting to try that out vs the Pan F. I want to try the Acros, though I have never shot it before under any situation.
The last reliable test data I have for Pan F Plus is from over a decade ago, taken from Robert Reeves' book on wide field astrophotography. He got a Schwarzschild factor of 0.76 for the film in testing.
I'll attach a .pdf chart of the adjusted exposure times for metered times out to 16 minutes, which you can use as a starting point. These are calculated with the standard Covington modified Schwarzchild formula, which you can find in several other posts on APUG.
P.S. Came back and added a graph of Reeves' findings for Pan F Plus in case you like that kind of thing. Both axes logarithmic.
Ok for what its worth... first night was very windy, so set up most sturdy tripod with weights.
Exposed three shots... Since they where single shots, have only developed the two longest ones.. of over 2 hours each, at f5.6...
Ha... both negatives clear as a whistle.. no image, ... yes, I took the dark slide out... (in fact put it under the water bottle to keep it from being blown away)
Doesn't make sense, two hours +.. heard the shutter click open, when I pressed on the cable release, and it locked the shutter open, and yes, heard it close when I released it later.
The first of the three negatives, which I did not develop, was exposed only for 14min, as suddenly behind me, hear a helicopter coming. Someone east of the Superstitions, must have needed help.. for you could see it near the horizon, way out there, with its lights flashing. So since it was early, 9:00pm+ went to bed and got up an hour later and started the second shot of the three.
Whats interesting, I'm not disappointed.
I'm going to try again, on another camping trip, into northern New Mexico, later this month. ;-)
Oh.. forgot to add... a storm front came in from the north, that's what all the wind was about, and brought clouds the next two nights, so no night sky to try on. :-(
That's how it always goes. I once believed that the Mamiya 7 glass brought in storms, because everytime I take it out I get crap weather.
What camera are you shooting again?