Skywatcher Auto-tracking dobs

[Vartigy]

I've just noticed this range of auto-tracking dobs on the skywatcher page.

http://www.skywatchertelescope.net/swtinc/product.php?id=159&class1=1&class2=109

I'm rather intrigued, seeing as I'm looking at going down that path for astrophotography.:question::D:camer a:

Anyone heard anything about these? Or seen them in Aus yet?
I wonder if they'll offer refit kits for those that already have the scope.

[mswhin63]

Can have a look at BTOW http://www.btow.com.au/telescopes-skywatcher%20reflector.shtml

[Vartigy]

Thanks Malcolm.
Yeh I bought my 8" off Keith.

I'm just wondering whether anyone on here has had the chance to play with one of these yet.

I'm rather curious as to how it holds up to astro photography.
Particularly the speed ranges. Wondering whether when used for imaging, there is the chance of blurring due to target moving at a rate not similar to the set speeds.
Or is this a common thing with all motorised mounts?

And I'd love to learn more on how this actually does the tracking.
Also, what does 'slew and track' mean exactly?

[mswhin63]

Not sure on that, I purchaced my DOB before the extra came out so I am making my DOB track. Might be worth to look at US site for reviews like www.cloudynights.com (http://www.cloudynights.com) or some other if there is anything at all. I have not noticed any comments as yet at least in OZ.

[Vartigy]

If you don't mind me asking, how are you planning on modding yours to track?

[mswhin63]

Firstly building and EK box for locating, then a Mel Bartel box for drive GOT and Tracking.

[Vartigy]

Building from scratch. Impressive, fair enough you must be a bit of an electronics guru as per your siggy.
Would love to see the final product of that.
Tough to construct?

[mswhin63]

Actually the EK is not hard at all. I have nearly finished. The most disappointing is serial communications on a non serial laptop. I am going to have the same prob on Mel Bartels with parallel connection.

[Peter Ward]

Unless you have a field de-rotator it will be rather useless.

[AlexN]

It would be ok for planetary work providing the tracking is accurate enough to keep a planet centered in the FOV for about a minute at very high focal lengths, but for DSO's, Peter is right, Useless..

[mswhin63]

I have OK on planetary and especially the moon without any tracking. I hope with the Bartel I will be able to enjoy viewing more so without having to re-adjust the scope, but with Bartel and EK I also believe that I may be able to do some good deep-sky with the right camera but not exceptional but a good starting point. Ultimately I wish to do Astro Photography but I like the opportunity to learn the sky by viewing. Also save the penny's

[Vartigy]

How so? Whats the function of it, and what does it correct?

[gary]

Hi Aaron,

Equatorial mounts are essentially the same as Alt/Azimuth mounts, such
as a Dob, except in an equatorial mount the Azimuthal axis is 'pushed over'
in elevation so that it is, for us in the Southern Hemisphere, then pointing
toward the South Celestial Pole.

One advantage of this is that the scope then only need track primarily in one axis,
namely the Az axis which is now called the RA axis on an equatorial mount,
in order to follow a star.

The other primary axis is known as the Alt axis on an Alt/Az mount and it
then becomes what is known as the Dec axis on an equatorial mount.
As the star tracks across the sky, the scope then need not move in Dec except
to compensate for small amounts of apparent motion that are caused by
atmospheric refraction.

If one uses an Alt/Az scope to track the stars, its motors need to be driving
both the Alt and Az axes simultaneously and what's more, the rate at
which those two axes have to be driven at is constantly changing. As a second
side-effect of tracking in Alt/Az mode, if you were to observe a field of stars through
the eyepiece over time as the mount tracks, they will appear to rotate around
an axis through the middle of the field of view. If you were to attach a camera and
take a time-lapse, rather than steady pinpoints of light at the same location, the
stars would appear to rotate within the field of view. This is known as
field rotation.

Some mounts add a third motor to where the eyepiece is to rotate the camera
as the mount tracks. Such a device is called a field derotator.

On large Dobs we have customers who take short exposure photographs of
DSO's and then stack multiple shots in software and use software field de-rotation.
The key then is to keep the exposure times short, which is at odds with the
desire to keep the exposure times long but beneath the noise levels to capture
the maximum amount of information. Nevertheless, some of these customers
have produced fabulous results with, for example, servo motor driven telescopes with
apertures in the 20" F/4.5 class.

Though most of the world's large professional scopes are driven Alt/Az and
use field de-rotators, it is not common to see field de-rotators in use when
you walk around the field of a star party. What are more common as
an imaging platform are then true equatorial mounts.

Because of the effects of atmospheric refraction, even equatorial scopes have
a limitation in that if the exposure times are long enough, some field rotation will
still occur. Some exotic telescopes, used for photographic sky surveys,
use an equatorial mount but then drive the scope in elevation (altitude) as well
to compensate for field rotation phenomena. For most enthusiasts, exposure
times are sufficiently short that any residual field rotation on an equatorial
mount does not impact the final image by any discernible amount.

Some Dob owners purchase or construct a device called an equatorial platform or
equatorial table. This is a motor driven 'wedge' that the Dob then sits on and it converts it
to an equatorial mount.

[Vartigy]

Gary, you are truly remarkable. Thanks for breaking it down so easily.
You've opened my eyes even more to the variety of options I have.
If these forums had the Karma rating going, i'd be giving you a hefty chunk of good karma for that post.
Thanks.