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(meteorobs) Video LM and Rates (was The Leonid Meteor Outburst of 1997)
On Tue, 20 Jul 1999, Sirko Molau wrote:
> only be done when the limiting magnitude is the same. Then I agree that a
> video system will be superior, since it has no 'dropouts' - it records
> everything (you only have to find the meteors on the tapes, which may
> bring you back to the original problem - visual meteor detection :-).
But you can have action reply. (-:
> You can modify the behaviour of a video system easily by changing the
> lens. When I put an 2.8/20mm wide angle lens at my camera, the fov is
> about 60 deg with lm near 5 mag. My 2.0/35mm lens gives an fov of 40 deg
> with lm near 6 mag. Finally, with the standard lens of my camera
> (0.75/65mm) I achieve about 8.5 mag at 20 deg fov. Thus, I can record in
> many different magnitude ranges. However, I made the experience that the
> overall number of meteors recorded per time interval is in the same
> order regardless of the lens, since the loss in fov levels out the gain in
> lm.
This was my expectation, but in light-polluted skies I did wonder if
the detections would be easier at higher magnifications because the
contrast improves. The angualr speed is only 2-3 times faster,
whereas for my telescopic observations it's twenty times.
On my system, until the Newvicon broke, I was seeing +7 with a 28deg
field (0.95/55mm) and a 2nd gen tube. However, I was more interested
in going fainter for the telescopic meteors and doing two-station
imaging with Geoff Grayer's similar system. When I inquired about a
fast catadioptric 135mm lens from STANO they never replied. Can people
please suggest sources of fast (<2.8) 100--150mm lenses?
Malcolm
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