"Anon" wrote in message
...
I will soon be taking delivery of a new Meade 16" LX200 GPS model and
have some fundamental decisions to make about its set-up.

I want to get more involved in imaging and plan to buy a CCD imager
after I have familiarised myself with the 16".

I have one basic question: Alt-Az or equatorial mount?

My understanding of the need for an equatorial mount is to assist with
tracking accuracy and avoid the field rotation inherent in anything but
short exposure imaging.

But, these days, with stacked multiple-short-exposure CCD images, can
the alt-az mount achieve the same results as an equatorial, especially
if the telescope is fitted with a field de-rotator?
Not really.
To actually 'record' an image, exposures must be long enough, for some
signal to be detected above the noise level. You can do amazing things
with a sequence of relatively short exposures, possibly getting one or two
magnitudes 'deeper' than would be achieved in single short exposures, but
the longer the baseline exposures (within the limits imposed by the
skyglow etc.), the deeper the 'set' will go.
The problem with using a field derotator, is that the tracking accuracy of
the final result, is dependant on three motors, all tracking together, and
tripling the error sources. It is also nearly impossible to use with a
guider, since the corrections that need to be applied are also rotating.
It's advantage is that it is quicker to setup. To get good results, there
is no substitute for multiple long exposures.

This would also avoid the difficulties of equipment clearance/eyepiece
position associated with aiming the scope towards the SCP which is the
region of some of our richest sky objects.
However the length of the derotator itself, adds other problems, and
decreases the rigidity of the whole setup. It is perfectly possible to
make a great setup using a derotator, but you need to be looking at
seriously more solid units than the ones commonly sold, especially when
using a reasonably large camera, and combining it with custom software, or
a seperate guide scope, to handle tracking. Generally, the accuracy of the
mounts sold on most scopes, are poor enough, that adding two more movement
errors is not the way to go.

I am going to build the pier myself, so it makes no difference to me
which one I build, but I would like to get the choice right before I
starting cutting and welding.

regards

Colin James
You will get better results with the scope polar aligned.
I'd have really asked this question beore buying the LX200!. You'd have
none of the camera clearance problems, using a GEM, and something like an
AP1200, with a C14, might well have been an easier permanent setup, than
trying to mount the 16" Meade on a wedge. You should be talking quite
heavy engineering for the wedge (1" plate), and remember that no matter
how accurate you think the work will be, you will need adjustment, so
welding all the joints is not an option.

Best Wishes