(meteorobs) Re: [RASCals] Re: Off-Topic X-ray film etc.

[Ed Majden]

on 9/4/05 4:24, Patrice Scattolin at scattol at videotron.ca wrote:


> Here's an example from 3M of x-ray film. All they say about it is that
> it's green sensitive.

Patrice:
    Thanks for the information.  This is what I found:

Ortho film,     

an X ray film sensitive to green light. Standard silver halide film absorbs
radiation in the ultraviolet and blue regions of the visible spectrum.

    In the early days when objective prisms were used for meteor
spectroscopy and prior to panchromatic films, ortho films were used.  This
was okay when using an objective prism, as dispersion in the red is poor
(crowded) where it is good at the blue end of the spectrum.  When objective
gratings started to be used, dispersion was more or less linear over a wider
range so it was desirable to have films sensitive over a wider spectral
range.  Panchromatic films had an advantage, as they covered a region from
around 3500A to 7000A or so.  Later extended red pan films were used
extending this to around 9000A in the red.  Millman/Halliday used a special
camera fitted with a transmission grating ruled on a quartz blank extending
the spectral response to around 3100 A. Below that atmospheric absorption
limits going to shorter wavelengths. They used Kodak spectroscopic 103-0
emulsions on glass plates.  Probably an expensive special order item now, if
this film is available at all.  Halliday presented a very interesting paper,
Publications of the Dominion Observatory, Vol. XXV, No.12, A Study of Ultra
Violet Meteor Spectra (1969).  Well worth a read if you can find a copy.
Today, for faint meteor spectroscopy LLLTV and image intensifiers are used.
These are sensitive from around 4500A to 9000A.  A manufacturer of image
intensifiers is trying to develop one with extended blue sensitivity but
they unfortunately will be rather expensive.  The Rayxar lens has many
elements with considerable distortion so I suspect it will not be very
useful.  Someone suggested using an uncoated enlarging lens with fewer
elements resulting in less absorption.  This may be worth looking into even
if these lenses generally have a slower speed.  To get a good spectrum on
film the meteor has to be rather bright, so it could possibly produce a
reasonable spectrum extending into the near UV.

Ed Majden