From: bjs@RUTS.ccc.amdahl.com (Barry Sherman)
Newsgroups: rec.photo
Subject: Re: Cibachrome printing (was Re: spotmeter questions)
Date: 14 Dec 92 20:16:14 GMT
Reply-To: bjs@RUTS.ccc.amdahl.com (Barry Sherman)
Followup-To: rec.photo
Organization: Amdahl Corporation, Sunnyvale CA

Ian Young ( > ) responds to a posting of mine ( >> ) (responding to a posting 
of his, responding to a posting of mine )  :-) :

>> I will grant that 
>> distressingly many of the Cibas that I see *do* have ghastly muddy shadows

>Sounds like you and I agree again :-)

Ack!  Now *this* is distressing!  :-)

>> But those shadows are symptomatic of poor printing, not a condition inherent 
>> in the material.  The solution is very simple.  Just take the time to burn the 
>> shadows adequately to assure detail.  (Remember, this is a reversal process so 
>> we increase exposure to lighten.)

>I've never had a big problem with overall contrast with Cibachrome
>(take a vacation in Scotland and you will quickly find out why, unless
>of course you can find out in advance which particular Tuesday Summer
>will be held on) partly because the low-contrast material was available
>over here much earlier than in the US, so I've always been able to use
>it.  But my style of B&W work involves a fair bit of waving of hands,
>cardboard and bits of wire while making the print and basically I found
>it impossible to make this work for Cibachrome.

Once again Ian's right.  I over-simplified.  Read on.

>
>> Granted, much of the time the shadows are too small and numerous for 
>> traditional burning and this has to be accomplished with contrast masking,
>> which is really just a way of doing finely gradated dodging the of highlights 
>> so as to permit giving the shadows adequate exposure.

>Is it really? I think there is a difference, which works in favour of
>masking and against traditional dodging and burning with Cibas.
>
>Consider a really boring transparency which has a light grey and a dark
>grey half to it.  You wish to make these tones the same.  If you do
>this by dodging or burning, you need a basic exposure time of, say, at
>least 10s.  If you now burn in the darker side (to make it lighter) you
>can do it in density terms but _it_will_change_colour_, maybe quite a
>bit, because Cibachrome has really nasty yellow/blue reciprocity law
>failure at these "long" exposures.  My suspicion is that if you use a
>mask, where all parts of the print are getting the same exposure
>_time_, this problem won't arise and the two halves will both end up
>the same colour.  Comments?

Yup, right on the money.  My description of masking as being the same
as finely gradated dodging of the highlights was fine as far as it went but,
for the sake of understandability, I didn't elaborate as much as I might have.
Ian's right about the color shifts.  They'll drive you mad.  Dodge back
an area (remember that this'll darken it in a reversal process) and watch it
go yellow.  Then burn another area and watch it go blue.  Dodging and burning
the sky and clouds, in particular is maddening.  So then you get smart:
Dodge an area longer than necessary (making it really yellow) and then turn
the blue (or subtract yellow) way up and burn it briefly with the
increased blue filtration.  And spend hours trying to get *that* balanced
right.  (I *have* done this but would prefer to avoid the pain in the
future.)  You'll run screaming to color negatives! (Which donl will gently 
tell you is probably where you should be to begin with! :-)

Masking will cause an increase in exposure.  Assuming that you were exposing
primarily for the higher values before masking and considering that the
mask has greatest density in the highlight areas, you'll have to increase
exposure.  This will give more exposure to the shadow areas, having the
effect of "opening" them and decreasing contrast, if you hold highlight
density constant.  The whole idea behind a basic contrast reduction mask is 
that you can give more exposure, thereby brightening the shadows, without 
burning out the highlights.  (There are people whose level of sophistication
allows them to make masks to selectively alter contrast in shadows, mid-tones
or highlihts but this is way beyond me.)

Assuming that you increase exposure through increased time you'll have the 
color shift toward blue caused by Ciba's reciprocity characteristics. But the 
difference between this and dodging/burning is that here the shift will be 
constant across the entire picture, not just an area which was dodged.  This is
because the exposure time increase is constant across the entire picture. So 
it's easy to adjust your filter pack to compensate for it.  Much simpler to
deal with, although the whole process of masking can get somewhat complicated.

Barry


--


|----------------------------------------------------------------------------|
| Barry Sherman, Amdahl Corp. | "It's much easier to go to exotic places and | 
| bjs@uts.ccc.amdahl.com      |  capture spectacular scenes than to take a   |
|                             |  spectacular picture of a really boring      |
|                             |  green pepper". - Anthony Tse                |
|----------------------------------------------------------------------------|
| Amdahl, being a corporation, is a legal fiction.  Therefore it is incapable|
| of holding, let alone expressing, opinions.  Unfortunately, this has been  |
| said of me as well. (I.e.  My statments are mine, not Amdahl's.)           |
|----------------------------------------------------------------------------|