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Re: (meteorobs) Normal lens

In a message dated 97-03-23 15:39:43 EST, you write:

<< 
 >to advance the film every 20 minutes...especially when I'm already
operating
 >a guided camera and advancing the film every 30 minutes or less.
 
 >>For meteor spectrosopy one does not generally guide the camera to follow
the
 stars.  The camera is mounted on a stationary mount and the stars are left
 to trail.  There is less chance of screwing up a meteor spectrum because of
 a guiding error.  Also, faint stars will produce faint spectra, thus less
 clutter on your plates.<<

Ed,
You miss understood me here. I don't have a guided camera for
spectroscopy. It is stationary. What I was talking about was that I'm also
using a 2nd camera that was guided. I usually let the film go for about 30
minutes in it...but with the spectra camera I was making 20 minute exposures.
What I was trying to relate was the big hassle of operating more than one
camera at the same time for different purposes with different exposures. 
 
 
  You'd have
 >to understand what is involved when I advance my camera's film. I once
tried
 >the scheme where I got a 20 foot long air actuated cable release with the
 >squeeze bulb held in my hand. I hold it while meteor observing from the top
 >of my observatory. 
 
 >>You will have to be very quick to open a shutter in time.  Professional
 systems have used photoelectric detectors to do this.  There is a problem
 using your eyes to do this.  The brightness of a meteor can be very
 deceptive.  I've seen meteors cross my cameras field that I was sure was
 photographed, but nothing was recorded on the film.  Also, I've recorded
 meteors that seemed too faint to be recorded. <<

yes indeed...very quick and it takes a lot of practice...and I do think I was
opening the shutters in time if....everything else was cooperating...that is
in the camera's field and bright enought. I figure that if I'm going to catch
a bright enough meteor to make spectra, it's going to be a fireball...and in
these cases, they are a little longer lasting. Hopefully giving me enough
time to catch at least part of it.  I practice by making exposures on
occasions on "the next meteor of any brightness that appears".  I'm not too
picky on magnitudes when I try to do it for "reals". Just about any meteor
that seems to be in the neighborhood of -1 or brighter I squeeze the bulb
automatically without regards to it's location or consideration of adequate
brightness to make a spectra. I haven't tried for spectra yet this way during
major showers...just too busy as it is. Perhaps I will this year if I'm
making longer open exposures.  I wanted to work out some other bugs first.  I
think acquiring a 4X5 lens of adequate size is what I need...now to convince
the wife...after I find the lens. 

 >>The eye is most sensitive to
 the green region of the spectrum and meteor radiation is generally stronger
 in the blue region where the eye is not as sensitive.  This is especially
 true of high velocity meteors such as the Perseids as the Ca+ lines are
 strong in high velocity meteors.<<

You are right about the green sensitivity for eyes... also blue and
Ultraviolet region being where most of a meteor's radiation is the strongest.

  >>Photoelectric detectors can be a problem
 also.  Gale A. Harvey from NASA/LRC found that lightning on the horizon
 would set off his camera shutters.<<
  
These critters are out of my capabilities in a variety of ways...that is the
photoelectric detectors...You've also given me some other ideas to kick
around.

I got another question about the box you made for your lens and 4X5 film
holder...how do you focus it? Is it pre-focused for one spot on your film
holders film plane? Can you somehow make minor adjustments? That is does the
lens somehow move back and forth? Do you have a fresnel lens mounted somehow
to see what your focusing?

What kind of film you use? You mentioned in a previous post about using Pan
1250 I believe?  I think this is the same thing as black and white Plus-X 125
in the 35mm format? Would you recommend another film with a little faster
film speed...such as HP-5 developed in Tmax as ASA 400? Have you ever tried
Light Hypering film for spectra purposes?

George Zay