(meteorobs) Re: Perseids etc>

[Ed Majden]

Hi Mike et al:
    Well, I'm starting to feel human again after an all night outing! ;-)
Yes Mike, off axis lights will give you a spectrum.  If they are bright
enough they can be way out of your field of view.  I check my cameras finder
but sometimes you can't see the spectra.  Time exposure often will created
an unwanted spectrum of a well off axis dim light.  As long as the meteor
spectrum does not overlap this can be ignored!  You don't want to overlap
star spectra either but sometimes this can't be avoided.
    I tried 1/2 hour exposures with my chopping shutter equipped
spectrographs.  Normally I shoot for 10-15 minutes without the shutter so it
will be interesting to see the background fog level on the film.  Just an
experiment.  I was shooting, more or less the same field of view with an
Optometric Blazed Grating and a thin film holographic grating so sensitivity
of each could be compared.  The literature on the holographic thin film
grating states that it has the same efficiency as a blazed grating in the
first order.  I very much doubt that, as the blazed side, of a blazed
grating is quite a bit brighter than the holographic spectrum when viewed
through the finder on the ground glass.  I expect it is 1 or 2 magnitudes
less efficient so you will need a rather bright fireball to record a
spectrum with the holographic grating, probably -3 to -4 magnitude.  In past
literature, Halliday states that you need a -2 meteor to produce a spectrum
with a blazed grating.  Objective prisms have a slight edge here.  I didn't
see any that bright last night.
    I have 6 exposures left on each roll so will use them up tonight if it
is clear.  Don't be discouraged if you didn't record a spectrum.  It is not
as easy as recording meteors with a normal camera.  Just keep trying!  Much
of this is just plain luck making it somewhat a sporting proposition!
    Anyway, good luck and keep me posted.

Ed Majden  AMS Meteor Spectroscopy
Courtenay, B.C.
CANADA 

PS: Anyone on meteorobs try spectroscopy?????