Reciprocity characteristics for Delta 100?

[tony_galt]

I'm working with this film for the first time and like the results. Something that annoys me, however, is spec sheet that I have for the film (same as the pdf file on it that can be downloaded from the Ilford site) which has a graph in it for 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 correction for exposures in the 1/2 to 3 or 4 second range. What are good guidelines for these shorter long exposures?

[walter_glover]

Tony,

 

<p>

 

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.

 

<p>

 

great film despite all of this.

 

<p>

 

Walter Glover

[harleyman7]

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.

[ted_kaufman]

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.

 

<p>

 

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.

 

<p>

 

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.

 

<p>

 

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.

[dave_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_gasteazoro4]

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.

[ted_kaufman]

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.

 

<p>

 

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.

[ted_kaufman]

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:

 

<p>

 

Corrected time = 1.15567 x (Metered time)^1.4379

 

<p>

 

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).

 

<p>

 

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.

 

<p>

 

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

 

<p>

 

Andrew