Even a film like Acros 100 or Tmax 100 will only get you up to about 8 minutes before reciprocity failure. If I was to try your experiment, I would probably do this: light the room with a dim red bulb, like a safelight bulb, and put a 25 red filter on the lens and go from there. At least that way you can get more light to the film and still be able to sleep.
I have a tested reciprocity chart that shows a metered reading for Tri-X of 10 minutes requires an exposure of about 9.5 hours. Tri-X ain't gonna work in this situation.
I used to make pinhole pictures in a darkened photo studio. During shooting sessions there would be light only from several shooting stations plus the odd occasions when all the overhead lights were on. The meter reading (f/180 or more) with the overheads was in excess of 30 minutes. I exposed Tri-X for an entire work-week and got very printable negatives.
Ah now I see what you're up to.
How about a low-wattage incandescent black-light bulb, in a lamp off in the corner somewhere. You eyes are rather insensitive to the deep blue/violet/UV light, but most films will see it quite well. RTP2 in particular. Yes, try it with fuji 64T, you might love it. Gorgeous blue colour shift. Should befit the subject.
I can actually sleep through just about anything. Not sure if other subjects can... But that's besides the point at this time. I'm really just trying to obtain the right balance of scene lighting and aperture to able to get an exposure over 6 hours. Thanks for the ideas. I'll try some of them out...
Choosing a film should be easy if you know the correction for reciprocity at 1 second indicated or estimated time. The failure at any othe time is in the same ratio. Thus, a film that requires a correction of 1 second will have 10 times the reciprocity failure of a film that requires a correction of 0.1 seconds. IIRC, that is about the ratio between Tri-X and either TMX100 or TMX400.
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Thoughts: You said, "picking an aperture at semi-random..."
Go wide open. Use a fast modern film like Acros. Acros is more tolerant of ling exposures than most other common films, and much more tolerant than Tri-X which is a "venerable" formulation.
In extreme dakness you need days or weeks of exposure. Look up the fellow, Abelardo Morel, who lights rooms with just a small pinhole and then photographs the room from within - great photos and they take many hours or a few days of exposure.
You may need to set up the camera and do cumulative multiple exposures to total a few days if the room is as dark as I think you mean. There has to be a little light to get anything at all. Something.
"Does reciprocity failure step in at some point and just end it?"
Reciprocity doesn't just end it, but it does make the film act as if it loses sensitivity at longer exposures. It is a gradual process of ramping up the compensation for lost "speed". Older film formulations are more prone to losses generally.
OK, I was right, facetious or not. It was a dark room.
Murray, I love those pictures. Thanks for posting them.
I used to turn my classroom into a Camera Obscura every spring and wondered what taking a picture of the picture and projected image in the room would look like.
My Kids used to get such a huge kick out of it.
Technological society has succeeded in multiplying the opportunities for pleasure, but it has great difficulty in generating joy. Pope Paul VI
So, I think the "greats" were true to their visions, once their visions no longer sucked. Ralph Barker 12/2004
I really like alot of Abe's work, too.
Inspired by the camera obscura take none step further, I am also stymied by a location/subject matter problem.
But time has passed, I think I found a half interesting location and a sympathetic ear/eye...in fact the person told me they were at a Morell exhibition, so I mentioned my idea...I think the ball is in my court right now.
Re: Acros, see Ryuji Suzuki's extended graphs for Acros, more accurate than the film datasheet. His stuff has been Wikified, so you make have to search a little.
From the equation found in the Unblinkingeye article, I compute that an exposure on HP5+ that is calculated to take 6 hrs without reciprocity misbehavior would take 327 hrs. I could not verify the equations beyond a few hundred seconds, but the line I got is headed in the direction of 327 hours. I could photograph my hand on a clear night here in the country by starlight in much less time than that.
The equation needs seconds for input and produces seconds as output, which is reasonable for most mortal photographers. 6 hrs = 216000 seconds. The calculation is:
Total time in seconds = t1*(tm^1.62). Divide by 3600 to get hours.
t1, the correction to be added to a 1 second exposure as measured by a linear meter, is for HP5+ 0.11 seconds from data by Howard Bond.
The symbol * means multiplied and the symbol ^ means "raised to the power"
As you can see, the value of the correction at 1 second is the factor that makes one film different from another. However, even a film that is 10 times better thab HP5+ would still require a 32.7 hour exposure for a a linear 6 hour estimate.