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Re: [APML] Photographic help with the upcoming Gemini's
Hi Chris,
The short answer is: Lots of very fast lenses.
50 - 85mm seems to be the sweet spot.
I have extensive information here:
http://www.astropix.com/HTML/I_ASTROP/I06/I0604/I0604.HTM
I'm sure you know most of it though.
Here's a shot of my setup that I used for the 2001 storm as well as some
detailed notes on what I learned:
http://www.astropix.com/HTML/F_COMETS/LEONID1.HTM
Here's a section from the first page that you might find interesting:
Meteors are essentially point sources. And recording, or seeing, point
sources is dependent on aperture. So the faster your lens, for a given
focal length, the more aperture it will have.
Extended sources, like nebulae, are dependent on focal ratio or the "speed"
of the optical system With extended objects, the faster the optical system
the better.
The fact that the meteors are moving adds other considerations.
A wide angle lens will capture more sky, increasing your chances of
recording a meteor. But the trail will be smaller because the image scale
will be smaller.
Lets look at the example of the same meteor captured on two cameras, one
with a wide angle lens, and one with a moderate telephoto, assuming that
the trail is short enough to fit inside the frame of the telephoto.
Since the meteor is essentially a point source, aperture is what counts here.
Don't be fooled by the apparent diameter of the front element of your lens,
in the 16mm fisheye, it is about 3 inches, but the true aperture is only 5.7mm.
You can go about 1.5 magnitudes fainter with each doubling of aperture. So
if I were shooting the 16mm at f/2.8 at 5.7mm aperture, and an 85mm f/1.8
shooting wide open at an aperture of 47mm, that would be about a little
more than a three times doubling of the aperture. So the 85mm can record
stars that are about 4.5 mags fainter.
However, the situation is complicated because the meteor moves. On the
telephoto it is on a given part of the film for less time. On the fisheye
it is on a given film grain longer, effectively giving it more exposure.
This is also complicated because the brightness, speed, and trail length of
meteors vary.
So, on one hand, you can record much fainter meteors with larger aperture
telephotos, but you have much less chance of recording one in any given
section of sky, not to mention framing it correctly.
I observed visually during the exposures I made during the 2000 Leonid
shower. I would guesstimate about 1/4 of the total time. In that time, I
visually observed around two dozen meteors, about 2/3 of which were
Leonids. So extrapolating, I would guess there would have been about 100
meteors total that night (adding in a compensation factor for not being
able to observe the entire sky visually). I know there were many faint
meteors in the frames of some of the cameras, yet they were not recorded at
all on the wide angle lenses, probably because the lenses just did not have
enough aperture.
Conclusions: if you have multiple cameras and lenses, be sure to shoot at
least one very wide angle and hope for bright meteors. If you have
unlimited resources, set up a gigantic cluster of 50mm lenses, and shoot a
mosaic of the entire sky.
Practically, you use what you have, you shoot wide open with a fast film,
you point it somewhere. Pay your money and take your chances.
Just be sure to go somewhere dark!
Jerry
At 01:55 PM 11/26/2004, you wrote:
>Hi all,
>
>A meteor photographer I am not, and I hope to hone my skills with the
>upcoming Geminids in mid December. As you may recall, I used my 28mm f/2.8
>lens and Konica 400 for gobs of 10 minute exposures pointing roughly east
>for two nights recently. Got one sporadic.
>
>So I ask all you meteor experts out there, What can I do different on the
>next run of meteors, to increase my chances of success? Faster film?
>bigger lens? Rub a rabbits foot? What's your "secret"?
>
>
>Novice meteor photographer,
>
>Chris
>
>---
>
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