Astrophotography Question.

roughplanet wrote:

Firstly, let me say that although I have read many books on
astrophotography, I am a rank amateur in terms of experience.
From what I have read (and it is, I suspect, common sense anyway), most
astro photographs, or at least many, are shot with the lens wide open.
But
almost all lenses are sharpest in the middle of their f-stop range, and
something I knew nothing about until recently; 'bokeh' or background
blur,
is prevalent (and in fact, desirable in portrait photos) in lenses with
larger apertures.
So which lenses are the most suitable for astrophotography, given the
above,
as obviously the uncorrected aberrations & bokeh present in (say) f1.4
50mm
or f2.8 135mm lenses would be quite undesirable for astrophotography.
Thanks in anticipation of your help.

"Robb Spring" wrote in message
...

Bokeh is best seen in a catadioptic lens. (the "cheap" 500mm lenses, on
ebay, that look like mak-cassagrain telescopes).
This is because the lens has a fixed focal ratio, usually F8, and a
factor of the mirror design, I believe.
With normal camera lenses, say an F1.4 50mm (a good overall lens), the
image will have problems around the edges of the photo, at 1.4 Fstop. Im
not certain why, I have read about it, but not experienced.
(I am learning astrophotography, too.)
You compensate by setting to F4 or F5.6, and increasing exposure length.
The 135mm will work too, but you will likely have to increase to similar
aperature settings.
Best overall webpage I found, for astrophotography, is the following:
http://www.darkskyimages.com/
The following page, is good, as well.
http://www.geocities.com/CapeCanaveral/Lab/6529/
Finally, read the following document at kodak's webpage.

http://www.kodak.com/global/en/consu...Contents.shtml

God bless,
-Robb

Thanks for the web sites. All of them have quite a lot to offer, and have
saved me wading through dozens of others.
Google can be such a pain nowadays, with 100's of sites for even the
simplest ask. What we need is a 'Condensed Google'; something similar to the
Readers' Digest's Condensed Novels :-).

Laurie