Digital BW, The Print

To be very precise about ISO ratings one should, ideally, run a series of test for each film/lens/camera/lighting combination.  Most people don't.  But, at the very least you need to know what your shutter speeds are.  Except for the developing process, the shutter is usually the most variable element in the process.  Although, with electronically controlled shutters, this may be changing as well.  Nevertheless, properly controlled, individually run test will account for all of the variations in a process including thermometer variances, etc.  Even with digital printing the resulting negative consistency is very beneficial.
 
For anyone that would actually undertake this type of testing, these testing procedures are detailed in Ansel's books, and other places.
 
It's rather amazing how your sense of control over the process goes up once you have successfully run such test.  
 
Tom Baker

C J Morgan <cjmorgan@...> wrote:
Clayton Jones writes:
>> ... I was dissatisfied and kept coming back to good old Tri-X at 200
>> (or 180 for the 4x5/320 stuff), with D-76 or HC-110.

Anthony G. Atkielski wrote:
> What's the advantage to the considerable overexposure, and how much do
> you adjust development to account for it?  

ISO film speeds are acquired by lab test which follow a very strict
testing protocol (and thank goodness, because that at least give
consistency). But those tests are done without a camera, and
so do not account for such things as bellows extension factor
or barrel extension factor (loss of light when a lens is not
focused at infinity). And even if that weren't a consideration,
it is still generally found that ISO marker speeds tend to be --
at least in negative films -- about 1/3 f/stop more than real
world shooting would ideally afford.

In other words, for about 90% of all users, a black & white ISO 400
film would be more ideally shot at an exposure index of 320.

And in consideration of any loss of light due to barrel extension
factor or (for view cameras) bellows extension factor, even better
to be shooting an ISO 400 negative film at a more optimum index
exposure of 250.

Now to the reason of why....

Negative films have some latitude to handle over exposure, but
very little latitude to handle any underexposure.

If I person shoots an ISO 400 negative film at 400, there is a more
than good chance that shadow areas will be clear and lacking in
detail. And if there ain't detail in that dark shirt you photograph,
then there's no way in the darkroom that lack of exposure can
be recovered.

People sometimes talk about "pushing film" -- deliberately 
underexposing and then compensating by overdeveloping.
Indeed, overdeveloping will increase the contrast of the
processed negatives so they can be printed. But no amount
of overdeveloping will bring back shadow detail which 
wasn't there when the image was first photographed. If
shadow detail ain't there at the time of exposure, no amount 
of compensation in developing can help with that.

So ideally, we adjust our exposures with negative films
to most make sure we have sufficient shadow detail.
And for 90% of folks, that means shooting an ISO 400 negative
film at exposure index of either 320 or 250 (i.e. either 1/3
or 2/3 f/stop from the suggested ISO marker).

Once this is established, only then is a person in a
position to determine what their best film developing time
will be and this has nothing any more to do with film
speed, but only determines how contrasty the negatives
will become.

And all of that gets summed up into a short phrase
B&W photographers have used for years and years:

EXPOSE FOR THE SHADOWS AND DEVELOP
FOR THE HIGHLIGHTS

(or more to the point, expose for adequate shadow
detail and find a developing time which gives the
image a good contrast range).

***********
   

> I've always exposed and developed as on the box; does 
> something improve with overexposure.

Try shooting your ISO 400 films at an exposure index
like 250 (that is to say, set your lightmeter to 250).

The seemingly slight overexposure will have you producing
negs which have more shadow detail and are easier to 
print because of this.

And you may also find that in shooting this way, the grain negs 
seem slightly less grainy (just like a few grains of sand
on the table look grainier than a whole bunch of sand on the table).

Then, develop as you normally do.

If you find that your end negatives seem too contrasty, then
next time, cut back on your developing times. And if your
negatives seem to flat, then slightly increase your developing
time next time. 

And just as a rough rule of thumb, an developing increase
of about 40% will be about equal to one paper grade.

And so, for example, if you find developing your negatives
for 10 minutes has them printing fine on a grade 3 paper,
then processing your negs for 14 minutes will have them
probably printing fine on a grade 2 paper.

**********

Anyway, hope that's of some help,
CJ



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