C8 advanced vs. Nexstar 8i

Looking at these two scopes: Nextstar 8i and C8 Advanced SGT, both with XLT
coatings....can anyone outline the basic differences. Which is the better scope
for photography. I know the Nexstar is more portable and lighter.

Thanks!

Robert

"Bobsprit" wrote in message
...
Looking at these two scopes: Nextstar 8i and C8 Advanced SGT, both with
XLT
coatings....can anyone outline the basic differences. Which is the
better scope
for photography. I know the Nexstar is more portable and lighter.
This is the 'Gem' versus 'fork' question (though the 8i, only has one arm
of the normal fork). To take photographs with a scope, using exposures of
more than a very few seconds, without 'field rotation' on the images
(where the stars at the edge of the image show curved trails), requires
that the scope is actually being moved round an axis parallel with the
Earth's rotational axis. With the fork mounted scope, this requires either
moving to the North/South pole, or putting the scope on a 'wedge', so that
it's base is parallel with the base of a scope standing at the North/South
pole. Hence to image with the fork mounted scope, you move away from it's
normal convenience, adding the wedge, and have the tripod, then a wedge
assembly on this, which has to be adjusted and aimed to put it in the
right position, and then the scope on top of this, sitting at an angle,
The Advanced SGT, instead is 'Gem' mounted. With this, the main (RA)
rotational axis of the mount, is adjustable, so you can set it to be
parallel to the Earth's rotational axis. This is made easier, by adding an
(optional) polar alignment scope, which fits inside the tubular shaft of
this axis, and allows reasonably good accuracy to be obtained in only a
couple of seconds. The assembly is 'three piece', as normal, with the
tripod, then the mount, and then the optical tube which attaches to this.
There is therefore the 'three part' assembly all the time, instead of the
'two parts' of the non-photographically mounted fork. That being said, the
extra time is tiny. For normal use, the heaviest component is lighter than
with the fork mounted scope, and normally people who are used to Gem
mounts, can be set up in no more than a very few seconds more than those
using a fork system.
In use the two 'photograhic' setups (Gem, or fork on a wedge), have their
own advantages/disadvantages. The fork is awkward to use near the poles,
with the eyepiece/camera, then having to sit directly above the base of
the scope. The Gem, avoids this, but has when you reach the Meridian, the
whole system has to 'reverse', and flip from one side of the mount to the
other.
I'm not sure whether the 8i, has an autoguider port as standard (the SGT
does). If not, this is another plus for the SGT.
The SGT, is closer to being useable as an imaging platform 'out of the
box'.

Best Wishes