[meteorite-list] Geminid pic / photographing meteors

From: John Hendry <pict_at_meteoritecentral.com>
Date: Thu, 16 Dec 2010 13:51:23 -0700
Message-ID: <C92FB708.A319%pict_at_pict.co.uk>

Chris,

To be clear about how I personally was looking at this; the length of time
the shutter is open has no bearing on the sensitivity to the meteor
exposure. That I thought was entirely controlled by aperture and ISO
sensitivity (i.e. "film speed"), along with the velocity, brightness and
trail persistence of the meteor. Camera field of view might also have a
bearing as the meteor image will spend a longer time over a particular
pixel sensor with a shorter focal length (i.e. wider field of view) and
thus be brighter in the image (though smaller). When you say "the longer
your exposure, the less sensitive you will be to meteors" then I can see
this from the point of view that the meteor exposure can be progressively
obscured by scattered light in the sky (from the
sun/moon/streetlights/background starlight) and from sensor noise in the
case of digital cameras. With sensor noise cancellation and a pitch black
sky, I would expect exactly the same meteor image from a 5 second exposure
versus a 30 minute exposure at the same f-stop and ISO, though the lower
magnitude stars (specifically those that haven't fully reached the cameras
upper exposure limit with the shorter shutter) will appear brighter as the
shutter is kept open longer. Is this about right or am I missing
something? I'm just not clear why I would lose fainter events with longer
shutter speeds other than for the reasons I outlined above.

I like your video idea... you could edit out all the dead action and make
something that looked like a much more exciting bombardment... though
jumping stars would probably give the game away unless you're using a
tracking mount. Plenty of scope for fun. Love your telescope images. M51
is just fantastic.

Cheers,
John





On 15/12/2010 11:34, "Chris Peterson" <clp at alumni.caltech.edu> wrote:

>Keep in mind that the longer your exposure, the less sensitive you will
>be
>to meteors. For maximum sensitivity to meteors, you'd like your exposure
>time to be no longer than a typical meteor lasts- say a couple of
>seconds.
>Anything more and you'll start losing fainter events. But with most
>cameras,
>if your exposure gets too short you spend more time between exposures
>than
>you do imaging the sky, and you start missing meteors or catching partial
>trails. 30 seconds is probably a good compromise.
>
>Using video is another solution. It maximizes sensitivity, but at the
>expense of total pixel count.
>
>Chris
>
>*****************************************
>Chris L Peterson
>Cloudbait Observatory
>http://www.cloudbait.com
>
>
>----- Original Message -----
>From: "John Hendry" <pict at pict.co.uk>
>To: <Meteorite-list at meteoritecentral.com>
>Sent: Wednesday, December 15, 2010 11:20 AM
>Subject: Re: [meteorite-list] Off topic- the weather IS getting worse +
>On
>topic Geminid pic
>
>
>> Thank you Carl. I did set out to capture half a dozen emanating from the
>> radiant with something earthbound in the foreground, but just too much
>> light pollution to hold the shutter open more than a couple of minutes
>> even looking completely at the sky. I think I'd cut it back to 30 secs
>>or
>> so during the successful frame to avoid blowing the glow on the clouds
>>too
>> much. I'll try again at the next promising opportunity, and make plans
>>for
>> a more rural location. I think you either have to shoot for a shortish
>> shutter exposure/wide angle to minimise star trailing or use a long
>> shutter speed to emphasise the trails. To my eye, very short star trails
>> make it look like you've got a dodgy tripod. I may keep my eye open for
>>a
>> used Meade and adapt the equatorial mount, but that approach would
>>cause a
>> smeared foreground if there were terrestrial objects in frame, though I
>> could get round that with multiple exposures.
>>
>> Regards,
>> John
>
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Received on Thu 16 Dec 2010 03:51:23 PM PST