What do I need for astro photography?

But isn't the image at prime focus really tiny ?

Depends on the instrument that delivering the image. My C-14 @ f/11
delivers a very respectable image scale whereas my ED80 @ f/7.5
doesn't.

The focal length is what determines the image scale you'll get. Prime
focus is pure but adjustable via optical amplifiers (which make it
less pure). If the image is too small, then you'd use a Barlow or
PowerMate to increase the effective focal length but the power of the
amplifier. Conversely, if the image scale is too large for your tastes
you'd use a focal reducer.

There are practical limits to how far you can push a telescope and
whether the image scale it's delivering is optimal for the chip
capturing the light.

So, can you tell me in more detail what the parameters are ? I have an f/5 12"
reflector and an EOS 350D (sensor size 22.2 x 14.8 mm), is this a reasonable
combination of focal length and sensor size ?

And how exactly is focussing done, trial and error or what ?


Cheers,

Boo

On Thu, 08 Mar 2007 12:04:49 GMT, Boo wrote:

So, can you tell me in more detail what the parameters are ? I
have an f/5 12" reflector and an EOS 350D (sensor size 22.2 x 14.8
mm), is this a reasonable combination of focal length and sensor
size ?

And how exactly is focussing done, trial and error or what ?


Trial and error, I think.
I found it to be a total pain in the arse on my first try the other
night. I had to line up the target in the eyepiece, flip the mirror to
the camera, and then try to focus it through the camera viewfinder.
Only thing is, it's so small and dim that you can't make much out at
all. I ended up with the Orion nebula looking like a cluster of orbs
and saturn looked like a street lamp.

On Thu, 08 Mar 2007 12:04:49 +0000, Boo
wrote:

But isn't the image at prime focus really tiny ?

Depends on the instrument that delivering the image. My C-14 @ f/11
delivers a very respectable image scale whereas my ED80 @ f/7.5
doesn't.

The focal length is what determines the image scale you'll get. Prime
focus is pure but adjustable via optical amplifiers (which make it
less pure). If the image is too small, then you'd use a Barlow or
PowerMate to increase the effective focal length but the power of the
amplifier. Conversely, if the image scale is too large for your tastes
you'd use a focal reducer.

There are practical limits to how far you can push a telescope and
whether the image scale it's delivering is optimal for the chip
capturing the light.

So, can you tell me in more detail what the parameters are ? I have an f/5 12"
reflector and an EOS 350D (sensor size 22.2 x 14.8 mm), is this a reasonable
combination of focal length and sensor size ?

And how exactly is focussing done, trial and error or what ?

Hi Boo,

Rather than me witter on about it, take a look at this page and it's
linked pages. There is loads of information to be had here...

http://starizona.com/acb/ccd/advimagingdetail.aspx


--
Pete
http://www.digitalsky.org.uk

Pete Lawrence wrote:


Rather than me witter on about it, take a look at this page and it's
linked pages. There is loads of information to be had here...

http://starizona.com/acb/ccd/advimagingdetail.aspx

Also check
http://www.astropix.com/

http://starizona.com/acb/ccd/advimagingdetail.aspx
http://www.astropix.com/

Thanks to you both for the excellent links.

--
Boo