Re: HP5, Delta films and reciprocity

In a message dated 7/21/2002 1:16:37 AM Eastern Daylight Time,
ragowaring@btinternet.com writes:

> I use the formula, y=.91x^1.51, where x is the metered time and y is the
> corrected time. It approximates the reciprocity pretty closely, and has
> worked for me for exposures up to 2 hours on FP4+, which shares the same
> reciprocity failure as HP5+. I've always processed normally, with pmk
> pyro.
>

Thanks for the formula! Just so that I can be sure that I understand, does
the '.91x' mean that you multiply x by .91? And I am assuming correctly that
^1.51 is means 'to the 1.51 power'? Could you perhaps give an example, say,
using the following:

If my meter says that the exposure is f11 at 1/125, then the exposure scale
for my camera says that approximate exposure is 3 sec. What would be the
final exposure calculation, taking into account reciprocity?

Does this formula work for Ilford Delta 100 or 400?

M Billingslea
Received on Sun Jul 21 14:50:24 2002