Densitometer Deficient or Zone VIII with an exposure meter

[venchka]

This got lost in the film test thread:




2) Use your exposure meter and meter through the negatives and pick the one that blocks light 1/3 of a stop more than a clear frame





OK, I did that. My reading for ISO 250 is 1/3 stop on my Gossen Luna-Pro. With a digital meter (Minolta Auto Meter IV), I get 0.3 for the ISO 250 negative and 0.4 for the ISO 200 negative. I guess my speed for HP5+ in Xtol is ISO 250.

Can I do the same/similar thing reading negatives with an exposure meter to find my developing time relative to Zone VIII? How many stops above fb+f or the Zone I exposure on the exposure meter should I be looking for?

Thanks for all your help.

[ic-racer]

Just a quick and dirty way of determining 0.1 log without a densitometer (which many people use to determine exposure index).

So, meter a uniform target and expose a series of negatives, placing the target at zone I. Vary your exposure index for the exposures and keep notes. Process the film and choose the negative that is 0.1 log above film base plus fog.

[venchka]

Thanks. I have done that for my minimum exposure to yield Zone I. What I would like to know now is what should my exposure meter say reading through a negative exposed for Zone VIII? I know that I need to vary development time to get to the correct density for Zone VIII. I was just wondering if I could use an exposure meter to read the various Zone VIII negatives. If not, I'll send the negatives to somebody to read.

[ic-racer]

A Zone VIII negative (at a printing exposure for 'minimum exposure for maximum black') that prints 'just off white' may be a better test than a density measurement of the negative. The 'darkroom' test above takes into account you light source, paper type and grade etc.

I think many people develop to a gamma around 0.6, so this would make zone VIII have a density around 1.26 (about 4 stops) using the crude approximation below:

SLOPE = Density/Exposure

SLOPE * Exposure = Density

Zone VIII is 7 stops more than zone I which is 2.1 log

0.6 * 2.1 = 1.26 log which is about 4 stops.


If you would like a reference from a published book, George E. Todd's book "Elements of Black and White Photography" cites the following goals:

Zone I: 0.1 (1/3 of a stop)
Zone II: 0.25 (1.2 stops)
Zone V: 0.7 (2 and 1/3 stop)
Zone VIII: 1.25 (4.2 stops)

[venchka]

ic-racer,

A thousand thanks! That will get me close. My darkroom isn't functional at the moment. Your help will get my development time close enough for the time being.

Thanks for your help!