Re: Determining exposure beyond.....................

Dear friends,

Can I find that Ilford reciprocity failure table on the web? On which sites
? Is there a similar table for T-max 100 ? Reciprocity failure is really a
problem. What if I'm working with lith film for half tone development later
on ? Thank you for any help.

Ricardo.

----- Original Message -----
From: Guillermo <penate@home.com>
To: <pinhole-discussion@pinhole.com>
Sent: Monday, September 17, 2001 2:34 PM
Subject: Re: [pinhole-discussion] Determining exposure
beyond.....................

>
> ----- Original Message -----
> From: "Rune Tallaksen" <tallaks@alfanett.no>
>
> > Can anybody help me with how to determine exposure when correcting for
> > resiprosity failure when the measured esposuretime exceeds that of the
> table
> > from the filmvendor?
> >
> > For instance when using Ilford HP5 Plus, the film data sheet gives the
> added
> > time for resiprosity failure until initial measured 35 secs(corrected
for
> > pinhole f stop). How can I calculate the "correct" exposure time beyond
> this
> > point? Tiral and error until now has not been satisfactory for me.
>
> One way to do it is by extrapolating the curve Ilford is giving you. You
> can do that mathematically or graphically. I usually do it graphically.
> Take the Ilford curve and reproduce it on a piece of paper, extend the "X"
> or horizontal axis to read the maximum "uncorrected" time you want and
then
> extend the curve with pencil trying to follow the same tendency, then is
> just a matter of extending the "Y" axis and graduating both axis. I just
> did that very quickly and the resulting extended curve gives me the
> following values, for 60, 90 and 120 secs of uncorrected exposure:
>
> 60 secs uncorrected = 475 secs corrected
> 90 secs = 925 secs
> 120 secs = 1900 secs
>
> Once you have the extrapolated curve, use it and if you get consistently
> somewhat overexposed film, that means the curve was done a bit to steep.
If
> film is underexposed consistently then the curve needs to be re-done a
> little more steeper.
>
> One thing for sure, extrapolating the curve would give you better
> reciprocity corrections than "trial and error".
>
> Hope it helps.
>
> Guillermo
>
>
> _______________________________________________
> Pinhole-Discussion mailing list
> Pinhole-Discussion@pinhole.com
> unsubscribe or change your account at
> http://www.pinholevisions.org/discussion/
>
Received on Wed Sep 19 21:22:55 2001