Re: [ATM] Betr.: 48" Dob at OMI

[Alexis Cousein <al@sgi.com>]

Don R Surles wrote:
> I do not understand what is being said in this post...but, you guys can 
> view with your naked eye and I will view with my 25".
> 
No argument from me. But it's not because the surface brightness is
larger that it looks better, but because every feature appears *larger*
- particularly important for night vision which isn't very sharp.

The point is that for large objects, though, there *are* diminishing
returns - there's no way  you can fit *the whole* of M42 in a 25" f/4ish
with an efficient exit pupil (not unless you invent the 180° apparent
field of view eyepiece first), so if your goal is to see the whole loop,
a scope beyond a given size no longer helps.

In fact, in a very dark sky, nothing can *quite* beat the aesthetics
of an 8" f/6 with a 2" eyepiece for looking at *the whole* of M42
floating in the space around it (and with the running man in full view).

There *is* a reason for wide field scopes, and even I have a
Starblast as a finder on my 16" Dob.

The 25" will still beat a 16" when you want to observe smaller contrast
detail on parts of M42 (in fact it's almost the ideal scope for looking
at M42 on a dark site, as in a 31T5 you still tend to see enough of
M42), but a 48" isn't going to show you the Big Picture at all on M42,
even though they tend to give spectacular views of the trap region.

Next time you pick an example, try M51 - you need quite a large scope
for that thing to overflow out of the field in a 31T5 Nagler ;).


-- 
Alexis Cousein                                  al@sgi.com
Senior Systems Engineer/Solutions Architect     SGI/Silicon Graphics
--
<If I have seen further, it is by standing on reference manuals>

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