Claudio Bonavolta wrote:
Nicholas O. Lindan wrote:
Some enlarging meters are also very good B&W densitometers:

http://www.darkroomautomation.com/em.htm

If you are enlarging the negatives then the proper place to
read the density is at the enlarger's easel. It gives you
the effective density in your equipment - taking into account
flare and calier effects.

If you are doing zone system calibration then what you want
is the EI and development time that gives perfect prints on
#2 paper in your enlarger, not some arbitrary set of densities.

You also need to find the total exposure to the paper
that results in almost not white and almost but not quite
totally black. The difference in exposure in stops between
these points is equal to the difference in negative density
you want for spanning Zone I to Zone IX.

--
Nicholas O. Lindan
Cleveland Engineering Design, LLC
Cleveland, Ohio 44121



Absolutely, any enlarger timer that gives an exposure time can be used
as a densitometer or to measure negative contrast too, an example with
my free softwa
http://www.bonavolta.ch/hobby/en/photo/darktools.htm
Which will be enough for the majority of printers, at least with silver
gelatin.

Said that, the use is not exactly the same and some densitometers offer
features that are generally not available in enlarger meters, like
reflection or UV densities measurement which are useful in other processes.

Claudio Bonavolta
http://www.bonavolta.ch

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Also, with using an enlarger will not give the same values as a
densitometer. Most densitometers are single diffuse instruments. A few
may be specular or double diffuse. But you know what you have.

Now if you are working for just yourself, and will not compare your
readings with anyone else, this may actually be better than with a real
densitometer.

But if you agree with Ansel Adams, and try to get a net density from
Zone I of your negatives to be 0.1, you probably will not know that
using an enlarger. You would need a calibrated step wedge to calibrate
the enlarger "meter" and it would drift around a lot.. My densitometer
has a beam splitter in it that sends half the light direct to a
photodetector and the other half through the negative under test to
another photodetector. The signals are routed through a differential
amplifier. This compensates for changes in temperature, changes in line
voltage, differences from one light source to another, aging of the
light source, ... . Typically, enlargers have none of this.

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