(Chris Greene) wrote in message om...

OK, I have a Pronto which I've truly enjoyed owning and using.
Recently I was all set to buy a TV85 when I was told by Dave Nagler I
wouldn't see that much of a performance pop between it and my Pronto
and would want a 4" to get a good step up. However, the Tak guy at TNI
said the 20mm boost of the Sky90 would be quite noticeable.
...
Anyway, I wonder what you all think about the above scopes in
comparison to the Pronto - is there enough of a performance boost to
make an net expense of $700-1300 make any sense? The *primary* use of
this scope (or any replacement) is my grab and go wide-field scope.

Boy, is that imponderable! Mostly, I suppose, it depends how much
$1300 means to you. It also depends how much the (rather severe)
chromatic aberration of the Pronto bothers you. You say that it
is OK, but if you put (say) the TV76 side-by-side against your
Pronto at 200X, the difference would be painfully obvious!
I try to avoid doing that, so I won't be tempted to spend more.

If you are serious about wide-field, then I would say no. After
all, all of the scopes listed above have max FOVs equal to or
smaller than the Pronot. But of course you are not -- you cite
the Moon as a primary target for your Pronto, and the Moon
*certainly* is not a wide-field target.

Between the extra aperture and the vastly better color correction,
the TV85 is certainly a big step above the Pronto for lunar and
planetary observing. Not so for wide-field astronomy, where
color correction is nearly irrelevant, and you will be getting
just a 20% increase in aperture. Not quite enough to justify
buying a new scope, as far as I am concerned. My rule of thumb
is that if you are going to make an aperture jump, you should
increase at least 40%, to feel that you are really in a
completely different league.

I recently bought Orion's Astroview 100mm F/6 refractor OTA as
a supplement to or replacement for my Ranger -- which has
identical optics to the Pronto. Despite significantly worse
color correction, the 100mm F/6 has so much more aperture --
twice the light gathering -- that it is really and truly in
a different league, especially for deep-sky observing but
also for planetary and lunar observing. It is also much
cheaper than the Ranger, which has its attractions!

On the other hand, it is also in an entirely different portability
class, more than twice as heavy and much bulkier. Of course, the
Pronto is also much heavier and bulkier than the Ranger. And
portability is more a matter of the mount than the OTA; as long
as your mount can handle the bigger scope, there is little loss
in portability.

- Tony Flanders