(meteorobs) Meteor photography and fisheye lens advice please

[Chris Peterson]

> I always thought that increasing the ISO would allow you to capture
> fainter meteors. Perhaps this is not the case after all then, and there
> is no need to lust after the latest DSLR's?

Increasing the gain beyond a certain point just equally amplifies the signal 
and the noise, resulting in no net improvement of S/N. It can be useful 
under certain situations, in particular where you need a short exposure 
under dim conditions. But with long astronomical exposures, those very high 
ISO settings are buying you nothing. You're still just counting photons, and 
once the gain is such that every photon collected contributes to the output, 
you've got all the information. Rather than thinking of the high ISO 
settings as high gain, you would be better off thinking of the low settings 
as low gain, useful when you have so much light you need to reduce 
sensitivity.

> How about the sensor's pixel density/size? I would expect the cameras
> with larger pixels to be better for light gathering ability/meteor
> photography.

Not a big issue for meteor photography, because you don't typically fill the 
available pixel well depth due to the short time the meteor actually spends 
on a pixel (and fireballs will generally saturate any sensor). With CCDs, 
and some CMOS sensors, larger pixels usually give greater dynamic range, 
which is very useful for typical long exposure astroimaging, but that's not 
what we're about with meteor imaging.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message ----- 
From: "Leo S" <l.stachowicz at btinternet.com>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: Friday, October 30, 2009 4:25 PM
Subject: Re: (meteorobs) Meteor photography and fisheye lens advice please


> Chris Peterson wrote:
>> Most likely for meteors you'll either be at ISO 400 or ISO 800.
>>
>>
> I tend to use ISO 800 or 1600 if it's not too light polluted.
>
> I always thought that increasing the ISO would allow you to capture
> fainter meteors. Perhaps this is not the case after all then, and there
> is no need to lust after the latest DSLR's?
>
> How about the sensor's pixel density/size? I would expect the cameras
> with larger pixels to be better for light gathering ability/meteor
> photography.
>
>> For exposure time, the longer the exposure, the lower your sensitivity
>> (sounds backwards, but for meteors it is true, because the sky background
>> washes out the meteor trail). So you want to make your exposures as short 
>> as
>> possible, keeping in mind that you lose some exposure time between shots,
>> and if too short you risk truncating meteor events. I'd consider 10-15
>> second shots, taken continuously.
>>
> This is what I aim for, for the reasons given above. The actual exposure
> time depends on how fast the sky-fog limit is reached.
>
> I would add, to keep the noise down in your exposures, you should
> over-expose very slightly. You don't want the background to be black, as
> this invites noise. Later on in post processing the actual levels that
> you want can be set.
>
>
>> If it's cold, the battery life will be annoyingly short, so get an 
>> external
>> power adapter if you plan on shooting over many hours. Make sure you 
>> shoot
>> RAWs, of course.
>>
> Agreed!
>
> Leo