From: Richard Sullivan FRPS (richsul@earthlink.net)
Date: 06/20/01-09:13:34 AM Z
Many many years ago I worked for a company called Spectrolab, now part of
Hughes. I was an optical technician. (I made $2.50 per hour!) One of the
things we made was spectrometers, gizmos that ran into the $100,000.00
price range in those days (1964-65).
They used a diffraction grating instead of a prism -- the gratings were
made by 3M up in the Arctic Circle on Hudson Bay! (Canadian Shield,
bedrock, little seismic movement.)
Light was passed across the grating and then output was measured at each
selected wavelength to determine is value at that point.
Measuring the sensitivity of a platinum print would require.
1. A light with a pure wavelength at each measurement point to determine
that prints sensitivity to that particular wavelength.
3. And this is the hard part. Light with enough energy to make an exposure.
4. Light to cover enough area of the print.
5. Good controls as to coating, development, etc of the print.
Since a pt prints requires a pretty heavy amount of light to become
exposed, this is quite a trick. We could not have done it in 1964 but then
things may have changed.
As for which print made under which conditions looks "better" tends to fall
into the "Golden Ear" phenomenon in Hi-Fi, which my long time friend Dick
Knoppow knows quite well as he is an audio engineer himself. (And by the
way, Knoppow is recognized as being an authority on motion picture
technology of the 40's and 50's.) I digress, but the point being is can we
measure, as Dr. Henry was doing, and measure what we see? Two sound systems
may very well measure the same with the best measuring instruments, but in
fact, may sound quite different, even to a Tin Ear like me. I think we may
have a similar problem in platinum printing.
A well trained ear hears things that aren't there. Zubin Mehta was/is a
notorious stickler for recording quality. he'd hear things the engineers
could not see on their instruments or hear themselves and only later did
they find the problem and correct it. Then all of his London recordings
sound unreal. But as Knoppow pointed out to me one time, they sound real to
him as he balances his recordings as he hears it from the podium, not as
you or I would hear it from the front row balcony.
This is an example of a musician "recording maker" much as we have "print
makers" in photography. I suspect like in photography, most conductors are
happy to take the limo back home after the concert and leave the recording
to the engineers.
--Dick Sullivan
At 07:34 AM 6/20/2001 -0400, you wrote:
>Judy Seigel wrote:
> > ...
> > I spoke to the brainiac at Voltarc, company that made the ...
>
>Yes, it is quite straight forward to measure the spectral output of a
>bulb with a scanning spectrophotometer, but as you mention each bulb may
>vary. I suppose the variation could depend of the quality of materials
>and manufacturer.
>
>However my interest is with the spectral sensitivity of the Pt/Pd
>coating. I have not see any information or research on the spectral
>sensitivity of these or any of the other alt-processes. It is fairly
>common that this information is measured by film manufacturers for their
>products, although averaged with the same variation possibilities as you
>pointed out for lamps dependant on their quality decisions.
>
>--
>Jeffrey D. Mathias
>http://home.att.net/~jeffrey.d.mathias/
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