From: bjs@uts.amdahl.com (Barry Sherman)
Newsgroups: rec.photo
Subject: Re: B&W darkroom question or how to increase contrast?
Date: 8 Sep 92 19:59:54 GMT
Followup-To: rec.photo
Organization: Amdahl Corporation, Sunnyvale CA

Gen M. Kanai writes:

>> I have some very flat (if that's the word) negatives. Can I increase
>> contrast more (when printing) by using two contrast filters together (as
>> opposed to one)?

>Well, you can stack filters if you want to, but that is like a doctor
>treating the problem not the cause.  You might want to make sure you
>dont have "flat" negs by checking your meter, maybe using filters,
>(orange/red) and properly setting your film speeds.

Negatives:

Extreme over/under exposure *can* produce flat negatives, I.e. all tones
on the toe or on the shoulder of the characteristic curve.  But in these
extreme cases, one usually doesn't even try to print them as there's really not 
enough to see in the neg to bother.  In general the cause is in the 
negative development, not exposure.  The rule is that exposure determines 
shadow density, development controls highlight density.  This is the most 
fundamental tenet of the Zone System, and it was this realization that allowed 
Minor White, Ansel Adams and their collegues to develop the ZS.

Under-development reduces highlight density without (much) reduction in shadow
density.  Why?  Because shadow development tends to go to completion (no
more silver halides left to be reduced).  But hightlight development
does not have to go to completion.  The more development, the more reduction of
silver in the highlights and the greater the density.

Increasing and decreasing highlight density while shadow density remains
more or less constant determines contrast.

If one's negatives are consistently flat, but have reasonable shadow
detail then increasing development time and/or temperature is the cure.
If they're consistently flat *and* lack shadow detail then exposure is
inadequate *and* development is lacking.

Development may be increased by 1)  Higher temperature.  2)  Longer time.
3) Increased agitation.  4) Higher concentration of developer.

>If you really need to print those flat negs, dont stack filters, get a
>contrasty developer with contrasy paper.  

Paper:

I doubt that stacking filters will help much.  If you're using Ilford
paper with Ilford filters, for example, I expect that the #5 filter is 
going to give you pretty much the maximum contrast that the paper has to
offer.  It may well be that other VC papers offer higher maximum contrast
but it doesn't seem likely that it would be more than 1/2 to 1 paper 
grade and in your case it doesn't seem as if that would be enough.

You might try increasing the concentration of your developer.  If you're using
Dektol 1:2, try 1:1 or even straight.  In general, increasing paper developer
time will have minimal effect on contrast, unlike negative developers.  As Gen 
said, some developers produce higher contrast than others:  avoid "soft" 
developers (I.e.  Selectol Soft) if you're having this problem.

>Better yet, stop shooting flat photos!

See above for suggestions in this area.  :-)

Barry

-- 


|----------------------------------------------------------------------------|
| Barry Sherman, Amdahl Corp.       | "Any fool can face a crisis - it's     | 
| bjs@ruts.ccc.amdahl.com           |  this day-to-day living that wears you |
|                                   |  out." - Anton Chekhov                 |
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