From: bjs@RUTS.ccc.amdahl.com (Barry Sherman)
Newsgroups: rec.photo
Subject: Re: Contrast mask for Ciba's (was Re: Chrome prints other than Ciba's)
Date: 18 Nov 92 20:06:25 GMT
Reply-To: bjs@RUTS.ccc.amdahl.com (Barry Sherman)
Followup-To: rec.photo
Organization: Amdahl Corporation, Sunnyvale CA

Anthony Tse writes:

>> Much about masking ciba deleted.
>
>	What kind of masking film do you use?  I tried TMAX100 and that
>plain doesn't work.  The film shrank after drying and the registration
>became way off, not to mention the boulder size grain.  

I first used FP4, a film with noticibly more grain than TMAX100 and had
no complaint about the grain.  I couldn't see grain from the mask in my
prints, even those made from 35mm.  But I had trouble getting rid of the pink
stain and did find that objectionable.  

When I started doing materials testing as described in Bob Pace's book on
Cibachrome printing I found that I needed a higher film speed in order to
get much of an image on the mask.  I wound up using TMAX400.  I found the 
masks made with this to be acceptable except that they were too dense.  Too
much density in the shadows.  The reduced development times/developer 
concentrations  required to get the low contrast desired resulted in longer
exposures and they resulted in unacceptable levels of fog.

Finally I broke down and got the stuff recommended in Bob's book and by 
professionals with whom I've spoken:  Kodak Pan Masking Film.  It's a trifle
more expensive than most b/w sheet films at ~$65 for a 50 sheet box.  But
it's designed explicitly for masking and to have a low Dmax and low contrast.
Using the techniques in Bob Paces book makes it possible to get the mask
exposure/development correct the first time on the majority of masks and that
helps to reduce the cost of masking and make the high cost of the film more
palatable for me.

Bob Pace's book on masking for Cibachrome printing was reviewed in the March 
1992 issue of Camera and Darkroom and is available from the author at:  (702) 
896-2515, complete with accompanying video, for ~$100.  And it's well worth
the expense, although his techniques do require a densitometer and his 
writing's terribly difficult to understand.  

Basically, what Bob Pace has you do is to determine the exposure scale of the 
paper you use, as exposed in your enlarger.  This is the density range of the 
original that can be recorded on the paper.  Then you use a Kodak three-step 
gray scale to make trial exposures on the masking film.  You find an 
exposure-time/development-time that yields the desired minimum contrast in the 
mask and another exposure-time/development-time that yields the desired maximum
contrast in a mask.   Then you can make a graph of exposure times and 
development times for producing various contrasts in masks.  Then you can 
compare the density range of the original with the exposure scale of your 
paper, determine the contrast required in the mask and use the graph to 
determine how long to expose and how long to develop the mask.  

Of course, there is a correction to allow for the fact that your original 
probably has an overall density which is different than the average density of 
the gray scale that you used in your materials testing.  And I'm finding that
I need a mask even when the density range of the original is within the bounds
of the paper and so am modifying the technique to suit my needs.  

I've not noticed any problem with film shrinkage with any of these three
films.   I have, however, heard people complain about unequal expansions/
contractions of the original and the mask and being able to print only when
the humidity matched that present when the mask was made.  I've not 
experienced this yet, though.  But I'm rather new to masking and am not
a good sample population.  Or, maybe since my darkroom has wet and dry sides
combined in the same room, the humidity is consistently high.  Or maybe
since most of my efforts have been with 4x5, these effects have been minimized.
I dunno ...

Barry


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Newsgroups: rec.photo