hp 5 reciprocity

[scott palmer]

Does anyone have a reciprocity chart for HP 5? Is it close to Tri-X? Thanks.

[tim atherton]

HP5+ ?


http://www.ilford.com/html/us_english/pdf/HP5_Plus.pdf (http://www.ilford.com/html/us_english/pdf/HP5_Plus.pdf)

[Walter Glover]

Scott,

Some time back David Carper (now sadly ex-Ilford) posted a formula which will approximate the curve that Ilford has determined by testing for reciprocity. The formula is:

Time (calculated) = Time (measured) ^ 1.48

where the caret symbol (^) signifies the exponential power

OR

Calculated Time = POWER (Measured Time, 1.48)

An example for an Excel calulation of a measured time of 10 seconds is:

=POWER(10,1.48)

= 30.2

I am also able to perform the same calculation on my palm Pilot using a spread sheet. I just tap in the measured time and another field shows the calculated time. Very handy but unfortunately does not address the issue of altered contrast.

[Andrew O'Neill]

Hi Scott,

I did my own testing for HP5+ and reciprocity about 6 years ago and have been relying on it since. I know it's better than the old Tri-X, but not sure about the newer version. Never tried it.
My data for HP5+ is:

1 sec = 1/3 stop more exposure

10 sec = 2/3 (1.5x)

100 sec = 2 stops (4x)

256 sec = 3 stops (8x)

No development compensation is needed.

You can take the data and make a curve which will give you inbetween times. Time on the bottom and stops on the side. Ilford's compensation curve gives way too much exposure compensation. At least that's what I observed.

[scott palmer]

Hey Guys,

Thanks so much for getting back to me so quickly! Great information. Now I can go back to work with confidence. It looks like the curve for HP 5 is different than the one I've been using for Tri-X, so I'm glad I asked.

[David Karp]

Scott,

Steve Simmons gives a chart with his findings for Ilford films' reciprocity characteristics. I have tried and find that it is right on target for my work. It is found in his book "Using the View Camera."

[Mark Mitchell]

Does anyone have a similar formula for other Ilford mono films?

[David Karp]

I believe that Simmons' book lumps all Ilford films together. I think that Ilford gives the same information for adjusting exposure due to reciprocity for all their films as well.

[Mark Mitchell]

Sorry, I was talking about the Carper formula (above) rather than the Simmonds book -- although does Simmonds say that all Ilford films have the same characteristics? If so then the formula would be the same.

[David Karp]

Mark,

If I recall correctly, David Carper's formula applied to all Ilford b&w films, not just HP5+.

[Mark Mitchell]

Hi Dave and all

Thanks for this -- most useful. I'll now spend a happy hour programming the Psion....

[Sidney Cammeresi]

Programming? I have a master's degree in Computer Science, but for computations in the field, I use a slide rule.

[Mark Mitchell]

I have a master's in Eng Lit so it's a *****ing miracle I know what an exponential function is.... Delighted to hear about you and your rule, though. Go you.