GOTO Mounts.

Post by **weixing** » Tue Jan 20, 2004 9:44 pm

Hi,
The field derotater will only compensate the field rotation, but it doesn't help to track accurately.

Actually, I think there isn't a mount in the market that will track accurately for long exposure yet. Since all current mount are "open-loop", so they will need a guide scope and a Auto-guider to close the loop.

Have a nice day.

Post by **Airconvent** » Wed Jan 21, 2004 1:00 am

Vince wrote:Thanks for all your replies. It means that the Nexstar 130GT will still be unusable for me coz I kinda intend to do AstroPhotography with it as well as piggyback AP. Darn...that means that if I go for the GOTO EQ mount, I'll still have to manually polar align first...darn..why can't they come up with something that doesn't require polar alignment and is relatively accurate for long exposures at higher magnifications!?!?

Btw, checked with Binoculars.com, the price is US$359/= (shipping was another US$230) compared to S$1350 if I get it locally.

The OTA is relative huge and its a single-fork-mounted design, so I'm sure vibration will be an issue especially during focussing and when there is wind. If the mount is anything like the Nexstar GT80, etc, then it will also be quite flimsy too...its still good for visual but not too sure if its suitable for serious astrophotography...

You need to align to polaris so that your scopes' rotation will be in sync with the earth's rotation. You can actually polar align without needing to see Polaris. You do this by observing the movement of stars and projecting where Polaris is. This takes time of course....
You can join the dempsey sessions when it happens and ask Chuang Yee to teach you. He is quite familiar with this....

rich

Post by **VinSnr** » Wed Jan 21, 2004 2:13 am

The field derotater will only compensate the field rotation, but it doesn't help to track accurately.

I didn't say it will track accurately. The original poster wants to know if there are scopes that need not polar align, yet could be use for AP. LX-200 + field derotater will do exactly that.

For tracking, no mount in the word is perfect. You still need to guide it. But doing digital AP with short exposures + stacking will do away the headache of guiding it for long.

addy · Post by **addy** » Wed Jan 21, 2004 5:48 am

U mean even the losmandy's and AP mount wont track accurately for long exposures.. then why on the earth they cost so high.. I thought the high end AP and Losmandy's are designed to track accurately for long exposures... hmmm

Post by **weixing** » Wed Jan 21, 2004 9:43 am

Hi,
A good mount can "place" the object in the Field-of-View for a very long time, may be one or more hours. This is very good if you are using it for visual observation, but not good enough for astrophotography. Astrophotography are very sensitive and demanding in tracking, especially at long exposure. Even a slight error will be reflected in the images.

But a good mount does help when come to astrophotography. A good mount will minimize the number of correction that require to only may be one or two correction every few minutes during the long exposure and the mechnical parts are so good and smooth that you can do the correction manually, without using any motor drive. You won't be able to do that on a lousy mount even you use motor drive.

Anyway, a good mount does make a great difference in visual and astrophotography, so that why they are so expensive.

Have a nice day.