Re: [APML] Meteor Photography Questions

[Jerry Lodriguss <jml@astropix.com>]

Alson,

Shoot wide open!  If you want meteors, that's the only way to go.

You simply can NOT make up for the reduced aperture and reduced ability to 
record faint meteors by exposing for a much longer time before reaching skyfog.

You have two separate exposures going on here at the same time, the meteor 
and the sky background. The meteor exposure is essentially a flash exposure 
that will be governed strictly  by aperture and f/ratio and film speed. The 
length of the exposure has nothing to do with recording an individual 
meteor. You could shoot all night at f/16 based on your thinking, but you 
probably wouldn't capture any.

The only possible argument for long exposures is that you want to capture a 
lot of meteors on one frame, but to do that you should be thinking of using 
a film with a LOT of reciprocity failure, so you can still expose long, but 
do it wide open.

If you want a really picaresque background, like with deepsky objects in 
it, then you'll have to use a film with good reciprocity failure, but 
you'll just have to bite the bullet and keep making shot after shot of 11 
minute exposures.  But imagine how little noise the image will have if you 
stack 16 of them!

I agree with Matt, then you just mask the meteors and stack the exposures 
(like Tony did last year), and it will look like a three hour exposure 
worth of meteors, if you want, and are lucky enough to actually get, a lot 
of meteors.

Jerry




Jerry



At 10:52 PM 10/30/2001 -0800, you wrote:
>I understand the benefit of using maximum aperture, but that also means 
>that the exposures must be shorter before reaching skyfog.  With ISO 800 
>film with p = 0.71 at f/1.8 and skyglow of mag. 20 per square arcsecond 
>(roughly the amount of skyglow at our site), ASTREXP estimates an 
>11-minute exposure for reaching skyfog.  At f/2.8, it's 40 minutes, and at 
>f/4 it's 1.8 hrs.  Thus, going one stop from 1.8 to 2.8 allows the 
>exposure to be almost four times as long, and going to f/4 almost ten 
>times as long, so I'm wondering if I can make up for the reduced aperture 
>and reduced ability to record faint meteors by exposing for a much longer 
>time before reaching skyfog.  I would not have the faint meteors, but I'd 
>get more bright ones because of the longer exposure.
>--
>Alson Wong
>Riverside Astronomical Society
>      <http://www.rivastro.org/>http://www.rivastro.org/
>Visit my Web page at:
> 
><http://home.earthlink.net/~alsonwong/index.htm>http://home.earthlink.net/~ 
>alsonwong/index.htm
>
>----- Original Message -----
>>
>>From: <mailto:reeves10@swbell.net>Robert Reeves
>>To: <mailto:astro-photo@seds.org>astro-photo@seds.org
>>Sent: Tuesday, October 30, 2001 7:52 PM
>>Subject: Re: [APML] Meteor Photography Questions
>>
>>There are a number of factors involved in successful meteor photography, 
>>and most of them are compromizes.  Stopping down your lens will rob you 
>>of the ability to record many meteors.  You need maximum aperture.  Also, 
>>wide angle lenses may increase sky coverage, but their smaller apertures 
>>limit the number of meteors you can record with a given film.  These and 
>>other factors are addressed on my web site at 
>><http://www.robertreeves.com/metphoto.htm>http://www.robertreeves.com/metp 
>>hoto.htm
>>As for films. personally I'm going to a dark sky site and use Superia 800.
>>
>>Robert 
>>Reeves                      <mailto:reeves10@swbell.net>reeves10@swbell.net
>>520 Rittiman 
>>Rd.                   <http://www.robertreeves.com>www.robertreeves.com
>>San Antonio, Texas 78209    210-828-9036
>>USA                                     29.484  98.440  200 meters

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