PDA

View Full Version : Tell me one good reason to ...

ebann
19th of November 2008 (Wed), 11:41
... get a 40D instead of the simple XS (aka 1000D) for astrophotography at prime focus using Live View.

The affordable models with Live View are: XS, XSi, 40D, 50D.
troypiggo
19th of November 2008 (Wed), 11:53
Can't help with your question, but you've posted this in the "astro photo sharing" section. Think you'd get better responses in the "astro talk/discussion (http://photography-on-the.net/forum/forumdisplay.php?f=126)" section?
ebann
19th of November 2008 (Wed), 11:57
Can't help with your question, but you've posted this in the "astro photo sharing" section. Think you'd get better responses in the "astro talk/discussion (http://photography-on-the.net/forum/forumdisplay.php?f=126)" section?

Oops... if some kind mod can move this I'd be grateful!
Olli
22nd of November 2008 (Sat), 03:43
Moved. :)
timeasterday
22nd of November 2008 (Sat), 08:47
Depends how picky you are about focusing. Personally, I prefer a measured FWHM through software. But that means having a laptop outside and all the extra cables and such. I still think the XT (350D) is the sweet spot for pixel size and noise when doing astrophotography. You could pick one of those up cheap and use the savings to get software or a knife-edge type focusing aid.
ebann
22nd of November 2008 (Sat), 09:22
Depends how picky you are about focusing. Personally, I prefer a measured FWHM through software. But that means having a laptop outside and all the extra cables and such. I still think the XT (350D) is the sweet spot for pixel size and noise when doing astrophotography. You could pick one of those up cheap and use the savings to get software or a knife-edge type focusing aid.

Hmm... what aids are these? Never heard about FWHM... what is it? I heard about knife-edge when grinding one´s own mirror...
timeasterday
22nd of November 2008 (Sat), 09:47
Here's a brief technical discussion of FWHM: http://www.noao.edu/image_gallery/text/fwhm.html

Basically the software measures the diameter of a selected star, and you keep taking test shots and adjusting focus while the software graphs the FWHM value. When you get to the lowest value, you have the best focus.

The usual hardware-type focusing aid I hear about is the Stiletto. There may be others but that's the one mentioned a lot. Have a look here:

http://www.stellar-international.com/digitalfeaturessf6.html