Light Meter Spectral Response

jjs wrote:

"Dan Quinn" wrote in message
om...
"jjs" wrote

We do not know how they test the film's spectral response.


B&W films are balanced for tungsten 2850 Kelvin. The film is
likely and very simply exposed to the 2850 Kelvin light source. Dan

I just cannot accept that until Kodak tells us just exactly what light they
use to describe their Tri-X (for example) in their spec sheet. It's
ludicrous, IMHO to assume B&W is to be used under 2850K.

Kodak's amd Ilford's spectral response plots are done by
completely different methods. Ilford uses a wedge spectrograph
fed by 2850K light. The wedge spectrograh (developed by Mees
at Wratten and Wainwright in 1907) uses a neutral density wedge
and a diffraction grating to project an image onto film of
the spectrum which is bright at the bottom and dim at the top.
This system does not provide the most precise measurements and
is generally inaccurate at the violet/UV end due to absorbtion
of those wavelengths in the optical system. Ilford appears to
have been using the same setup for ages, so it is probably pretty
valid to compare different graphs from Ilford for different films
at different times. It is proably impossible to make valid
comparisons (other than very rough ones) between Ilford's
data and anyone else's.

Kodak nowadays uses a much more complicated system which uses
a calibrated source which produces 10nm bandwidth sections
of the spectrum and records the amount of energy at each wavelength
required to produce a standard density level in the film. This
appears to be a very exact measurement.

I've got some old Kodak data from the 1950s with wedge spectrograms,
and I'm not sure at what date Kodak changed their methods.

Peter.
--

"jjs" wrote in message
...
"Q.G. de Bakker" wrote in message
i.nl...

But i'll definitely retire from this thread now.
You believe what you want to believe. And i'll stop being amazed about
people who talk authoritatively about a subject, yet display ignorance
about
the basic concepts involved.

All rant and no information. You have well earned a place in my killfile.
I
will refer to your messages as excellent examples of childish argument and
evasion when I teach freshman rhetoric
.

Teaching freshman rhetoric is like hitting your thumb with a hammer,
deliberately, repeatedly. I know, I've done it.

--
Regards,
Matt Clara
www.mattclara.com

"jjs" wrote in message
...
"Q.G. de Bakker" wrote in message
i.nl...

But i'll definitely retire from this thread now.
You believe what you want to believe. And i'll stop being amazed about
people who talk authoritatively about a subject, yet display ignorance
about
the basic concepts involved.

All rant and no information. You have well earned a place in my killfile.
I
will refer to your messages as excellent examples of childish argument and
evasion when I teach freshman rhetoric
.

Teaching freshman rhetoric is like hitting your thumb with a hammer,
deliberately, repeatedly. I know, I've done it.

--
Regards,
Matt Clara
www.mattclara.com

In article ,
"Matt Clara" wrote:

"jjs" wrote in message

will refer to your messages as excellent examples of childish argument and
evasion when I teach freshman rhetoric
.

Teaching freshman rhetoric is like hitting your thumb with a hammer,
deliberately, repeatedly. I know, I've done it.

Both? or One inclusive?

--
LF Website @ http://members.verizon.net/~gregoryblank

"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918