The topic at hand, the ED-100.

The last thread about this scope got badly off track and I am hoping to start
anew and this time I hope we can stick to considering the ED-100 and just where
it might fit into the scheme of things.

My thinking...

One can judge a scope based on the design parameters and in so doing an 4 inch
F9 with an ED objective is not something that appeals to me at first glance.
My initial reaction to this scope was, too slow, too long....

I had guessed (and posted several times), based on the ED-80, that any 100mm ED
scope from Orion would be about F9.4, not the 100mm, F6-7 scope that everyone
dreams of.

But in reality the 900mm focal length is not as bad as it sounds, in fact it is
not bad at all. When making the field of view calculation for the terrestial
section, I realized this scope can give some nice widefield views, in fact,
this scope has about the same capability because of the 2 inch focuser as a
500mm FL scope with a 1.25 inch focuser.

With a 42 mm widefield eyepiece, it will be at 21X with a greater than 3 degree
FOV and a 4.6 mm exit pupil, that really should be quite nice. And if it lives
up to its potential in color free performance, this should be a scope that
could not only do the widefield stuff with a nice well corrected field of view,
but also operate at high magnifications as well. May be TeleVue wasn't so
silly with the TV-102.

Three Degrees is Good, color free at 200X is good.

There are plenty of folks who are quite happy with their Celestron 4 inch F10
refractors, they seem to do a nice job on double stars and reasonable job on
the planets, this new Orion Scope would be a natural upgrade that should
hopefully just fit right into place and provide a significant improvement in
color free performance.

So, while I do like Newtonians for a variety of reasons, I also know that a
refractor like this does have some real advantages, especially when EQ mounted.
Certainly the robustness and closed tube of a refractor is nice, no worries
about dust on the mirror and no worries of damage while cleaning it. Cooldown
and collimation are also non-problems.

Another advantage of a refractor like this is that it is not so big that it is
out of the question to use it for long range birding or other terrestial
viewing. One is certainly not going to hike down a canyon with it but setting
it up along a water way or at the top of a canyon should be great fun. With a
42 mm widefield eyepiece, it will provide 21X @ greater than 3 degree FOV,
certainly a reasonable low power for doing birds, 3 degrees is certainly doable
and the higher power stuff should be nice.

And as someone who has tried birding with a variety of Newtonians, (including
my 12.5 incher) the erect image of the refractor plus the eye piece position at
the rear is certainly far more ideal since most targets are about horizontal or
even below the scope.

My experience with 4 inch F9 APO's is limited to a few quick looks at Mars
through Ron Bee's TV-102, certainly those were nice and sharp and color free to
my uneducated eye. But as we know, Ron has done a lot of serious viewing
though his "Light Cup" and it has allowed him to develop into a talented
observer.

So the bottom line for me is that this scope surprised me because itactually
has a lot of potential as to do just exactly the things I like to do. Wander
about the night sky with a competent scope just enjoying.

It seems it has the potential to be a great general purpose astronomy scope,
short enough focal length to give some nice widefields of view but long enough
focal length to allow the ED objective to perform nicely at high
magnifications.

While it is not a scope I would necesarily choose, it is a scope that I think
will be very popular if it is comparable to its smaller brother, and then it
should provide some real pleasure and joy to just about everyone who uses it.

Best wishes and Clear skies

Jon Isaacs

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