RE: Best CI for process

Just for the record, I actually plot average gradient, not CI. But
both methods of determining slope give almost the same results, at
least for most practical photographic applications, I generally just
use the term CI rather than average gradient since more people seem
to understand it.

Sandy

>Sandy,
>
>In the context of your practice can you define dmin, dmax, and density
>range for me? I've found different authors use these terms (especially
>density range) as if they are speaking to some commonly accepted
>standard, yet they often derive them differently.
>
>One of the nice things about Contrast Index is that it is defined quite
>precisely and is unequivocal.
>
>Thanks,
>
>Joe
>
>>>> sanking@clemson.edu 10/02/05 12:14 PM >>>
>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 12:51:49 2005