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Re: (meteorobs) Normal lens



George Zay wrote:

>Ed,
>Okay....if we used a 35mm camera with it's normal lens...the 50mm at f/1.4
>for example. Would you get a good spectra with a variety of emission lines as
>good as let's say if you used a telephoto 135mm f/2.8? This is assuming that
>a sufficiently bright meteor crosses the field. Would you see more lines with
>the 135mm than the 50mm? How about a 200mm at f/3.5 compared to the 50mm? I
>know for the 200mm that the area of coverage is smaller, but would you see
>more lines if the meteor was bright enough?
>George Zay

You could use a 35mm Camera with a 50 mm fl lens for spectroscopy but I
would not recommend it.  The normal meteor spectrograph covers a region from
350.0nm to 650.0 nm.  This is 300.0 nm long or 3000A.  With a 600g/mm
grating on a 50mm fl lens you will have a dispersion of around 323A/mm
approx.  Lets say, 300A/mm.  This will give you a spectrum about 10mm long.
The H & K lines of Ca11 will barely be resolved.  They are at 3938A (H) and
3934A (K) lines, only 4A apart.  Other compound lines will just be blends as
they will overlap each other.  You will not get much info from such a
spectrum.  Using a telephoto lens will increase your dispersion but your
field of view will be so small, that you would be very lucky to record a
spectrum.  It's difficult enough as it is. The minimum format I would use is
2 1/4 square with a 75mm fl lens.  Even that is not great.  4X5 format with
a 150mm fl lens would be much better.  High resolution spectra are what is
needed.  Ed

  
-----------------------------------------------------------------
Edward Majden                         epmajden@mars.ark.com
1491 Burgess Road                     Meteor Spectroscopy
Courtenay, B.C.                       CCD's - P.E.P.
CANADA  V9N-5R8                       Amateur Astronomy