Eastman 7222 Reciprocity Law Failure
Posted 07 January 2009 - 07:35 PM
What is the formula for reciprocity law failure?
Posted 07 January 2009 - 09:05 PM
I'm expecting to have to expose 7222 beyond 1 second. How do i determine it's reciprocity for it. I've looked everywhere, however i can't find the model for this film.
What is the formula for reciprocity law failure?
I have waited for someone more knowledgeable in this area than I to respond... so far no one has.. so here are my thoughts as you may be desperate for some sort of direction.
CAUTION: Take this with a grain of salt.
Reciprocity has more to do with color than contrast in an image (generally) when it come to reciprocity failure. Since you are shooting B&W, you have some elbow room. I would not hesitate to run a total of a Pola or ND or another B&W Filter or combination of Filters to a total Light Loss of 8 stops... accumulative (ND 24)... we have done this many times with no noticeable effects (S16 to HDCam - Spirit) on Color Neg... numerous times.
I would not hesitate to go ND30.. after that I do not know.. but I may be wrong and that ND30 could cost me .. where is the edge!!!!!
Posted 07 January 2009 - 09:49 PM
Also, you were mentioning some LARGE compensation numbers there for those long exposures (24!? 30!?), so is it cumulative (adding) how many filters you're using depending on their individual exposure factors, or is there like multiplication involved in this? Finally, this stuff is listed in the film documentation, isn't it? So how would you normally meter, your settings, and then make the adjustments?
I know--I'm an idiot. But what else is new?
Posted 07 January 2009 - 10:07 PM
Correct me if i'm wrong. Is 2, 4, and 8, 1/2 light, 1/4 light, 1/8 light, thus being 1stop, 2 stop, 3 stop.
Eastman Double-X (7222) has a reciprocity rating from 1/10000s to 1second, once it goes beyond that compensation by adding time to the exposure is necessary. IE, if my exposure was 10seconds, i would have to add 3 seconds onto the exposure time in order to compensate for reciprocity failure. However, i have been told that different films have different reciprocity ratings. I imagine because Motion picture cameras rarely go beyond this exposure time they don't bother researching beyond it.
David, do you have any stills from projects you have shot with so much glass infront of the film? I'm curious to see how it turned out.
Posted 08 January 2009 - 01:37 AM
Except by testing!
As you are doing the smart thing by asking this question in advance, and presumably it is some kind of special shoot that you don't want to mess up on, the best guide would be to shoot a few frames of a grey card, at the shutter speed you plan to use, bracketing from the metred exposure upwards a couple of stops or more. You don't say if you are looking at 2 or 3 seconds, or 2 -3 minutes (ore more!)Shoot a grey card at normal running speed, and see what exposure you need to match the density at your extended time.
The graphs in this sitehttp://silvergrain.o...eciprocity.html aren't very easy to make sense of, and they don't refer specifically to 7231, but the stills version of Plus X is probably very similar.
As I read one of the charts, you would have lost about 2 1/2 stops of speed by the time your exposure reaches ten seconds. That might be a starting point for your tests.
BTW, yes, 0.3ND is one stop, 0.6 is 2 stops, 0.9 is three stops. and so on. A 2.0ND filter is 6 2/3 stops, and a 3.0 ND is ten stops. You don't often see then referred to as factors, but 1, 2, and 3 stops would require x2, x4 and x8 exposure (ignoring reciprocity).
Posted 08 January 2009 - 03:35 AM
David, do you have any stills from projects you have shot with so much glass in front of the film? I'm curious to see how it turned out.
3.0 ND Wratten gel filters used to be widely available until recently, they are still available online. I saw some 3.0 a couple of years ago at a local photo shop. These particular ones were small though, they would be more for behind the lens use, maybe they could be put in front of a small diameter c-mount lens. You can order from B&H and the like though.
You may find it hard to operate a camera with 10 stops worth of ND in front (or behind) the lens. For pictures of solar spots and the like, fine. But otherwise it could just be VERY tricky to operate a motion picture camera under those circumstances and get good results. I don't enjoy filming with more than 3 or 4 stops worth of ND myself.
What are you going to be photographing / filming at such extremes, pray tell?
Posted 08 January 2009 - 07:34 AM
ND3 - 1 stop
ND6 - 2 stops
ND9 - 3 stops
ND12 - 4 stops
Pola - 2 stops
85 - 2/3 stop
..and yes.. it is accumulative.. for daytime time lapse I will often run a Pola + 85ND9 + ND6 for a total light loss of 7 stops. Generally we have to remove the filters to set the frame... lock off the camera then replace the filters as with them in you could barely see even the sun if it was directly in frame.
Are you doing time lapse or are you doing 1 second exposures because there is so little light where you are shooting?
Edited by David Rakoczy, 08 January 2009 - 07:36 AM.
Posted 08 January 2009 - 08:02 AM