Reciprocity characteristics for Delta 100?

[Tony Galt]

I'm working with this film for the first time and like the results. Something th at annoys me, however, is spec sheet that I have for the film (same as the pdf f ile on it that can be downloaded from the Ilford site) which has a graph in it f or determining exposure correction for longer exposures. The trouble is that the scale of the graph is so small that it is hard to read accurately the proper co rrection for exposures in the 1/2 to 3 or 4 second range. What are good guidelin es for these shorter long exposures?

[Walter Glover]

Tony,

Another irritating aspect of Ilford's reciprocity table is that it offers no suggestions for processing modification. I think, also, that a close inspection will indicate that they use the same graph for all their emulsions - I might be wrong.

great film despite all of this.

Walter Glover

[Don Sparks]

Steve Simmons book "Using the View Camera" has a reciprocity chart for most B&W films including Ilford. Acording to Steve, reciprocity times for all Ilford films are the same. I have used his times with HP5+ and FP4 with great success. I carry a laminated copy of this chart in my camera bag.

[tedkaufman]

Gordon Hutchings (PMK guy) has a very useful reciprocity chart in the back of his book, "The Book of Pyro." He claims Ilford films do not gain contrast during long exposures. No exposure correction up to 1 sec, then 2=3, 3=4, 4=6, 5=8, 10=21 for Delta films.

I made a table of reciprocity corrections which I reduced to very small size and printed out so that I could tape it to the handle of my Minolta spotmeter.

While I have found Hutchings exposure times quite accurate, I don't agree that Ilford films do not require contrast adjustment. I find that with a 10 second exposure, I need N-1.

You might be interested in Acros, which I now use for all my night shooting. Acros requires no correction at all up to 120 seconds, then only +1/2 stop thereafter. And no contrast correction at all. That makes it the fastest film on the market once you exceed 30 seconds of exposure. It also has a slight rise on the shoulder, with a gentle slope, which produces highlights that look quite similar to the translucent, pearly look of Delta 100. I just wish Fuji would distribute 4x5 in the US, and while I'm at the wishing table, I wish they'd make an Acros 400! Incidentally, you can buy Acros in 4x5 from Badger Graphics.

[David Schaller]

Ted, I too have taken to Acros. Where did you get this reciprocity information? Have you taken shots up to 120 seconds with no correction? I'd love to have some hard data to be sure before I take a long exposure...it's a bit expensive to do all the testing myself. thanks, Dave Schaller

[Jorge Gasteazoro]

Ted could the lack of development compensation be due to your developer and its compensating properties? I know you use a special developer of your own making that is based on Catechol and has compensating and staining properties.

[tedkaufman]

I've done lots of long exposures with Acros, and I've never encountered any excessive contrast buildup. I've developed very long exposures, up to 10 minutes, in my catechol developer and in Gainer's vit-c developer and the contrast has been perfectly normal.

On the other hand, many night shots have an extreme brightness range, especially here in NYC. So, obviously, under those conditions, compensation processing is required. But it is required because of the brightness range, not reciprocity.

[tedkaufman]

The reciprocity information I posted earlier for Delta films was taken from Hutching's Pyro book. Fuji lists the reciprocity information for Acros on their website.

[Andrew Pell]

Try the following equation:

Corrected time = 1.15567 x (Metered time)^1.4379

This is from curve fitting the Ilford data in the leaflets and is virtually spot on for this level of accuracy (r squared = 0.999).

One Ilford guy at a show couldn't believe that anyone could find out their "trade secrets" like this but it's fairly easy with a bit of time and a spreadsheet / decent calculator.

Hope this helps (or at least lets you create your own graphs / tables)

Andrew

[jppoli]

Tony, from my experience, you can expose:
45 seconds for 30 seconds measured
2 minutes for 1 minute measured
5 minutes for 2 minutes measured