RE: Best CI for process

Eric,

Sorry, but a part of my last message was omitted during cut and paste.

What I meant to have said was that although density range and CI (or
Gamma, Average Gradient or whatever you want to call it) are related,
the use of the former to talk about negative contrast can be very
misleading because it often does not provide a good indicator of the
effective printing density of a negative, while CI nearly always does.

For example, consider the following three cases, which correspond to
data from testing I did of TRI-X film, at nine minutes, 13 minutes
and 20 minutes.

Time Dmin Dmax DR CI
9:00 .23 2.80 2.57 1.0
13:00 .30 3.11 2.81 1.0
20:00 .45 3.35 2.90 1.0

As you can see, the DR increases significantly with time of
development, but the CI, which is a much better indicator of
effective printing density, does not. The negative developed for nine
minutes will print with exactly the same contrast as the one
developed for twenty minutes, though the extra B+F of the twenty
minute negative will require more printing time. In other words,
increasing time of development to obtain a higher DR range over that
needed for maximum CI is just a waste of time which also results in
longer printing times.

Of course, if you are working with a film that has very linear
straight line curve there will be a better correlation between DR and
CI.

Sandy

>Sandy, I know they are.
>
>Eric Neilsen Photography
>4101 Commerce Street
>Suite 9
>Dallas, TX 75226
>http://e.neilsen.home.att.net
>http://ericneilsenphotography.com
>
>> -----Original Message-----
>> From: Sandy King [mailto:sanking@clemson.edu]
>> Sent: Saturday, October 01, 2005 11:03 PM
>> To: alt-photo-process-l@sask.usask.ca
>> Subject: RE: Best CI for process
>>
>> Eric,
>>
>> Density range (DR) and contrast index (CI) are closely related.
>>
>> Read about it.
>>
>> Sandy
>>
>>
>>
>>
>>
>> >
>> >
>> > So a discussion of density range may be more appropriate than the CI
>> for in
>> >camera negatives intended for use in platinum/palladium printing?
>> >
>> >
>> >
>> >Eric Neilsen Photography
>> >4101 Commerce Street
>> >Suite 9
>> >Dallas, TX 75226
>> >http://e.neilsen.home.att.net
>> >http://ericneilsenphotography.com
>> >
>> >> -----Original Message-----
>> >> From: Ryuji Suzuki [mailto:rs@silvergrain.org]
>> >> Sent: Saturday, October 01, 2005 7:19 PM
>> >> To: alt-photo-process-l@sask.usask.ca
>> >> Subject: Re: Best CI for process
>> >>
>> >> From: Richard Knoppow <dickburk@ix.netcom.com>
>> >> Subject: Re: Best CI for process
>> >> Date: Sat, 01 Oct 2005 16:36:06 -0700
>> >>
>> >> > Is it possible for you to post it on your web site
>> >> > perhaps as a PDF, I think it would be of considrable value.
>> >>
>> >> PDF papers are ideal in my view but I am reluctant to do this to my
>> >> photographic paper file. I'd rather mail a photocopy to someone in
>> >> serious, legitimate need of the information.
>> >>
>> >> Although I might not condemn anyone putting scans online quietly, I
>> >> probably don't want to know if my copy has anything to do with it.
Received on Sun Oct 2 10:14:29 2005