Yesterday I asked for opinions on this, especially cf a 300/4.5 + 2XA.
Thanks Chuck, C.H., Moose, Earl and Jeff for very helpful responses.
I'll explain a little more.
I already have a 300/4.5, and like it a lot (this was the lens that
brought me onto this wallet-opening list a couple of years ago).
In fact, I've used it a couple of times in TOPE entries:
http://www.tope.nl/tope_show_entry.php?event=17&pic=31
http://www.tope.nl/tope_show_entry.php?event=22&pic=4
The 300/4.5 + 2XA is the longest focal length I can do.
I've used this combination a little. The only one I have scanned was
taken a few minutes after the above TOPE22 pic:
http://www.cs.adelaide.edu.au/users/andrew/photos/moon.jpg
Now this to me is a touch fuzzy, especially around the moon.
For a moment I thought it might be the chroma CH mentioned, but more likely
non-optimal telephoto technique, plus possibly losing something with the 2XA.
So what occurred to me was that Sigma mirror might not only be lighter and
easier to use, perhaps even less susceptible to vibration, and might even be
easier to focus (at f8 rather than f9).
And that it might also give optically better results than the 300 / 2XA. I'm
still not enough convinced of this latter point to go for it on that basis.
I'm now reassured that the Sigma is a well built and capable performer,
with the low contrast a bit of a worry.
Now I've been thinking about what I want from "more telephoto". It would
be mostly to take pictures of small birds. Especially the highly elusive
wrens et al that flit frustratingly around our favourite campsite. So then
I would want to stick the 2XA on the mirror lens to get an unfocusable
1200/16. :(
So I'm going to pass on this one and do some more background work.
There are some interesting things in the spreadsheet Chuck kindly sent
me offline, like the 1250/10 Celestron. More dollars of course ...
The 600 that prompted all this is actually on eb*y, item 7531541381.
Aus only, but if anyone OS is really interested I would volunteer to
take delivery, give it a thorough "test" and post it on. :) Noting
that it's located in the far north of our wonderful state of South
Australia, I'd check first that it has not been exposed to dust -- the
infamous red bulldust of the outback. Unlikely but ...
regards
Andrew
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