Delta 3200 Reciprocity failure
Does anyone know what the reciprocity failure rate of Delta 3200 actually is?
I have seen the chart in the datasheet but I was wondering how close that is to reality. Alliteratively are there any ways to improve reciprocity failure for long exposures. (I like to do night sky shooting, so 5+ minutes at F2.8 is something I think about)
Reciprocity differs depending the actual conditions, Ilford's chart is nothing more than a rough guide. I recently did some practical tests with Fomapan 200 and found it's reciprocity wasn't anything like Foma's recommendations.
So do your own tests, waste a roll or two of film to get it right.
See the article "LIRF is Lurking at Your F-stop" at www.unblinkingeye.com. It doesn't show that film, but shows a way to minimize the experimentation required to get it.
If you are looking at such long exposures consider Acros or TMX. You're camera is already sitting on a tripod and the reciprocity failure of those films is quite small in comparison to most. You may actually end up with a shorter exposure.
From someone who has film astophotography experience, these fast 3200 films have among the worst reciprocity and found them to be practically useless; They're dead before you open the shutter. Slower Films generally have better effective long exposure speed. These 3200 films are only good for for having the aperature wide open ie 30sec tripod shot- 50mm lens @ f1.7. If you have good sky transparency and want a balance of raw speed for around 5 minutes, HP5 from what I read is probably the best. The best film for long expoure at the moment is Fuji Acros 100, excellent reciprocity which I have tested. This would be the better choice probably for anything longer than 4 minutes but I have found that Acros doesn't respond well to push processing (HC-110) and best develop it to nominal speed. So, if your not going to much longer than 5 minutes maybe HP5 is the better choice, also with lattitude and flexibility in development in mind.
One simple technique that is noted in improving reciprocity is to pre flash the film with light to innitiate the smallest but noticeable density in the film. You will just have to experiment in order to optimize this personally.
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I've used Delta 3200 for long exposures and found the corrections given in the datasheet to be woefully inadequate—all my negatives came out severely underexposed. As others have said, you're better off choosing a slower films like Tmax or Acros, which have little reciprocity failure compared to "conventional" films. You will actually end up with a shorter exposure time using one of these films than with Delta 3200, sometimes by several stops!
Last edited by E76; 06-06-2009 at 11:44 PM. Click to view previous post history.
Two words: Tmax 400
Almost as good reciprocity performance as Tmax 100 and Acros 100, but with two more stops of speed. It's amazing film.
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Here's a graph comparing the necessary exposure for Acros, TMX, and Delta 3200 at the same light levels. Acros and TMX are assigned ISO 100 and Delta 3200 is assigned ISO 1000. The Acros line is a best fit curve for Kit Courter's data at the Lunar Light Photography web site. The TMX curve is a best fit for Howard Bond's data in his Photo Techniques article on reciprocity failure, referenced many other places on APUG. The Delta 3200 curve is from Michael Covington's 2000 test of Delta 3200 that resulted in a Schwarzschild exponent of 0.65. covingtoninnovations.com
The x-axis is metered exposure in seconds for ISO 100. The y-axis is the exposure needed to compensate for reciprocity failure. The curve for Delta 3200 is shifted to account for it's higher ISO, so the x-axis values are not correct for the Delta 3200 curve, but the relative positions of the curves on the graph are correct for reciprocity adjusted exposure under identical lighting.
It's difficult for lower reciprocity failure in the 100 ISO films to overcome the initial speed advantage of Delta 3200, which is what places the Delta 3200 line so much lower at the y-axis. TMX grows closer to Delta 3200 at the 80-160 second measured time for 100 ISO, but it will be a long time reaching the shorter exposure time needed for Delta 3200 with it's higher initial ISO, if indeed it every gets there. Acros is the clear champ in overcoming reciprocity failure, but it still doesn't catch up with the ISO 1000 Delta 3200 until Acros requires a metered 930 second (15.5 minute) exposure and Delta 3200 needs a metered 93 second exposure, at which point both films need about 1085 seconds of exposure to overcome their respective reciprocity failure.
A lot of people make the statement that slower films can 'quickly' overcome the speed of faster films with poorer reciprocity characteristics, but they often don't take into account the relative metered exposures needed under identical working conditions, and this overtaking of higher speed films by slower films happens less often and less quickly than they imagine.
Given Covington's tested Schwarzschild exponent of 0.65, you can calculate reciprocity adjusted times from metered times as follows:
adjusted time = (metered time + 1)^(1/0.65) - 1
Plug that into a spreadsheet and print out a chart that will give you a good starting point for Delta 3200 reciprocity failure. There are batch to batch variations in film, and you may need to adjust the Schwarzschild factor up or down a little to fit your usage.
BTW, you should always assume that numbers like these are approximate, as there is always a lot of variability and experimental error where reciprocity failure is involved. Test for yourself. You could also use the Schwarzschild numbers to generate a Gainer factor for the equation he uses for reciprocity failure, as shown in the article he references. You'll likely end up within 1/3 of a stop (or closer) of the same exposure if you compare the two methods with the appropriate factor/exponent.
Last edited by Lee L; 06-07-2009 at 01:15 AM. Click to view previous post history.
Has anyone who is saying to use other films considered that the OP might want to do this with Delta 3200 because he likes the unique way the film looks? That is what I assumed, at any rate.
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Of course beauty is in the eye of the beholder, but I thought this series from Steve DiRado was amazingly successful. I have seen all of the prints in person and they really work. They were shot on T-Max 3200.
The series can be seen at:
Originally Posted by Todd Niccole