Re: [APML] Leonid Film Queston

[Jerry Lodriguss <jml@astropix.com>]

>
>I'll be shooting the Leonids next month with three Nikon lenses:
>
>1) A zoom lens at 35 mm at f/4, 5 minute exposures, pointed at the radiant;
>
>2) a standard 50 mm at f/4, 5 minute exposures, pointed at the zenith;
>
>3) a zoom lens at 100 mm at f/5.6, 1 hour exposure.
>
>For the one hour shot, I'll probably use hypered RG200 per the recent
>discussion.  What do you recommend for the 5 minute exposures?  The goal is
>to capture the faintest possible Leonid.


Hi Dave,

If at all possible you should re-think how you are going to do this... You 
really need fast film and fast lenses.

The hypered film won't help at all except for capturing the background like 
a normal deep-sky shot, but you would have to be exceptionally lucky to 
perfectly frame a really bright fireball in that small area to have any 
chance of capturing a meteor. You won't capture any faint ones, or even any 
medium ones at f/5.6 with 200 speed film.

The 35 and the 50 have to be faster than f/4, don't they?

If anything, I would point the longer lens at the radiant because if you 
capture anything there it's going to be head on, and will be just a point, 
so if you imagine the meteor coming right at you, the length of the time it 
is visible it will be on one spot of the film, so should accumulate photons 
there, so you can get away with slower film and f/stop. But even still I 
wouldn't shoot 200 speed film, even hypered. Hypering won't really help at 
all for the meteors.

The length of the exposures don't really matter in terms of capturing an 
individual meteor because you could think of the meteor as a flash 
exposure. Only the f/stop will matter there. If you goal is to capture the 
faintest meteors possible, you need the fastest lenses you can get and the 
fastest film.

There is an optimum combination, I think this was previously discussed by 
Robert Reeves.  It boils down to aperture, film speed, angular coverage on 
film, brightness of the meteor, speed of the meteor, and, I think, luck. <G>

Wide angle lenses keep the meteor on a shorter portion of the film for a 
longer period of time, which helps with the exposure per film grain, but 
the physical length of the trail on the film is shorter.  Long fast 
telephotos with big apertures (in absolute terms) will capture the faintest 
meteor (think of them as a point source that moves), but cut down on your 
chances of capturing one mathematically because you are covering less area 
of sky.  Choose your own poison.

I know you probably know all of this already.  I have some more info on a 
web page at:

http://www.astropix.com/HTML/I_ASTROP/METEORS.HTM

Jerry



Jerry


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