> ....the print may look fine, but
> not reflect accurately the range of tones found in the negative. This
> could be tested with a step wedge, but you would need a good reflection
> densitometer to evaluate the tests.
Sandy, Risa, et al.: Perhaps I wasn't clear enough about the method I used
for testing: I did *not* expose under a negative. I saturated an entire
sheet of paper with dilute cyanotype emulsion and gave it a very brief
exposure. I then examined the print both before and after development,
looking for any signs of "stripes", that is anything following the line of
the bulbs to suggest greater or less exposure. The reason for the very
weak exposure was that "D-max" or equivalent would tend to mask
unevenness.
My prior experience with step-tablets and densitometers had led me to
believe anomalies and artifacts of both the tablet and the densitometer
would mask the kinds of *slight* difference I was looking for. For
instance, on my densitometer (Macbeth) with three drops in a row, odds are
you'll get three different readings,slight or not so slight. For the
practical purposes of personal darkroom the instrument is fine, but for
testing even illumination of this nature, not. As for the step tablets
themselves, they also show variations from tablet to tablet, again
probably greater than actual differences in illumination (if any) would
cause.
In sum, I did not trust usual testing methods to give me this information.
What I devised may also author false assumptions -- which was why I asked
the group at large for input on the subject. So far, silence (perhaps
turkey-day whiteout?).
Howwever, somewhere in the back of my mind (and in the archive!) is
someone's statement that a light source such as a bed of fluorescents is a
light *area* (or something like that) which would by its nature be even.
That may have been from Mike Ware, or.........???
Finally, as for whether better bulbs up or bulbs down -- The bulbs up was
easier to make & destroy, but the bulbs down, in which you have a separate
contact frame of some sort and slide it under the fixture, has the
advantage of accepting dodging or masking more readily. The fixture I'm in
the process of making (read "having made") is supposed to be reversible,
that is, I could use it bulbs up for informal testing, having only to lay
out paper and step tablets on the cover glass, but could turn it over for
serious *printmaking* with state-of-the-art contact frame.
The almost-finished object has, however, sat several months waiting for a
hinge: The plate glass across the top proved too heavy to be comfortably
lifted alone by a weak woman such as myself. Plan was made to put it
on a glass hinge. First hinge was wrong, ate the glass. A better hinge
is to be arranged....
Cheers,
Judy