wrote:
This question is within the context of the subject title.

ALL things being equal, if HP5+ is given X minutes to
develop, what is the value of the constant K in the equation
X times K equals Y. Y is the time needed to develop Delta 3200.

I think the value of K may hold steady for all films in the same
developer. If so, some film, Plus X perhaps, may be used to
establish base times and a constant K applied to each
of any other films in that same developer.

To the point, I've from the woods ONE roll of Delta 3200 to
develop. If ten minutes will do for a roll of HP5+ how many
minutes should I give the Delta? Or, by what factor should
I multiply the ten minutes? Dan

The factor will depend upon the developer, film, EI and temperature. I've went
through this in detail when I wrote a program to calculate development times for
films plugging in the following variables: developer, desired contrast index,
temperature, and film EI. However, it was written before Delta 3200 was on the
market, so I didn't include data for that film. Just about every estimate of a
"constant" required non-linear regression (500+ combinations).

If you're trying to estimate a time for Delta 3200 based on a known HP5+ time
for a certain temperature, EI and CI, check the Ilford film PDF's for both films
and the developer you intend to use. If there's a problem, post your HP5+ EI,
developer, time and temperature.