From: boutzev@lcaohp2.epfl.ch (Lubomir Boutzev)
Newsgroups: rec.photo
Subject: Multigrade paper exposure part 3
Keywords: multigrade , b&w , photo
Date: 8 Apr 92 09:05:36 GMT
Article-I.D.: sicsun.2750
Reply-To: boutzev@lcaoap1.epfl.ch
Organization: AI crazed sickos.

PART 3

reminder
Parts 1 and 2 are required prior this part.

GRADE DETERMINATION
We know by now the limits of the exposure for the shadows and the
highlights.

Now it's time to work out how we can use this information for the determination
of the last variable in the exposure-grade binomial.

When the negative is exposed we can assume that every point of this negative 
is illuminated for the same time during the exposure.

This meats that for a given exposure time and a starting point (either the shadows 
or the highlights) the other limit point is controlled only by the negative's density.

In other words, if you fix the correct exposure time to obtain the proper
exposure of the point  ((Log(emax) , Dmax)), you don't have any additional control
for the point (Log(emin)  , Dmin).

Inversly if you fix the proper exposure for (Log(emin)  , Dmin) you have no means to 
control the correct exposure of (Log(emax) , Dmax) .

Is this completely true ? Not exactly for that's the point grades step in.

Grades are in fact used to adapt one extreme exposure point when the first one is
determined.

We shall now see the two basic exposure/grade determination methods for 
B&W printing.

THE SHADOW PRIORITY
In this method we shall assume that the exposure is determined in a correct way for the 
point (Log(emax) , Dmax) . The measuring aids required will be further explained
in this text.

In other words, out positive will have shadows just black enough before saturation
starts.

The Highlights (darker points of the negative) are thus determined by the 
contrast of the negative itself.

We must find a way so we can ensure that our priority point (Log(emax) , Dmax) 
and the corresponding highlights point (Log(emin) , Dmin) fit in the non 
saturation zone of the paper.

This can be done by selecting the appropriate grade allowing you an exposure
latitude equivalent to your negative's one.

In other words the grade of the paper will be the one ensuring the correct exposure of
both the priority point (Log(emax) , Dmax) AND the corresponding highlights point 
(Log(emin) , Dmin) .

Verification of the correct results is easy, assuming the processing steps are
correct (fresh developper and correct processing times and temperatures).

(1) If you applied this method and instead of the nice deep detailed shadows you find:

-Grey stuff without too much details
	THEN your point (Log(emax) , Dmax) is underexposed
	AND you must increase the exposure time , go back to (1)

-Black swadows , saturated without too much details
	THEN your point (Log(emax) , Dmax) is overexposed
	AND you must decrease the exposure time , go back to (1)

-Nice deep detailed shadows
	THEN your exposure time is correct
	AND go to (2)

(2)  If instead of the nice clear detailed highlights you find:

-Grey stuff tending to dirty black with overcontrasted details
	THEN your paper grade is too low
	AND you must increase the grade , go to (2)

-White zones without details
	THEN your paper grade is too high
	AND you must decrease the grade , go to (2)

-Clear detailed highlights
	THEN your paper grade is correct 
	AND your print is correctly exposed for the time found in (1) and
	the grade found in (2) , go to (3)

(3) You can wash & dry this print and frame it.

This was the trial & error method. It can be of course applied  in real printing but
it's given here for comprehension and troubleshooting purposes. The exposure
time & grade are intended to be determined by the means of measuring devices.


THE HIGHLIGHTS PRIORITY
This method is just the opposite of the previous.

The point (Log(emin) , Dmin) determines the overall exposure time, giving thus
priority to the highlights.

A similar set of rules can be given for this case.

(1) If instead of the nice detailed bright highlights you find:

-White zones with no details
	THEN your exposure time is too low
	AND you must increase the exposure time , go to (1)

-Grey or dirty black zones with details 
	THEN your exposure time is too high
	AND decrease your exposure time , go to (1)

-Nice detailed bright highlights
	THEN your exposure time is correct
	AND go to (2)

(2) If instead of nice deep detailed shadows you find

-Black saturated shadowd with no details
	THEN your paper grade is too high
	AND you must decrease the grade , go to (2)

-Grey or dirty shadows
	THEN your paper grade is too low
	AND you must increase the grade , go to (2)

-Nice deep detailed shadows
	THEN your paper grade is correct 
	AND your print is correctly exposed for the time found in (1) and
	the grade found in (2) , go to (3)

(3) You can wash & dry this print and frame it.

Same remarks as in the previous method.



CHOICE OF THE EXPOSURE METHODS 

OK for now dear friends, no time for further writing today.
Check for parts 4 and more.

L. Boutzev
boutzev@lcaohp1.epfl.ch

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