Guiding a Dob?

[Kaptain Klevtsov]

Today we had some discussion about why you can't take photos with a Dob. mounted Newt., as well as some comments refuting the arguement. Well i got to wondering if it would be possible to build a platform to sit a Dob. mount on that could take it's cue from a guiding system like that used with a GEM.

The concept works like this, the platform has three supports, a pivot at the North or South end (roughly) and two other supports in the form of motorised jacks placed at the other two corners of an equilateral triangle. The two jacks would move constantly at a rate slightly slower than necessary until boosted into a faster movement by the guiding system.

The advantage of this system would be that the north / south alignment wouldn't need to be so accurate as the guiding system would compensate.

I'm not going to build one anytime soon and there's no Patent Pending issue so for the sake of discussion I throw this one to be torn to shreds by you guys who can see the flaws (or be bothered to do the sums).

So the question is:- Is this another dumb idea or what?

Enjoy.

Captain Chaos

[GazOC]

Couldn't you just use (say) a set of Meade DS GOTO motors on the Dobs alt/az and use the platfrom to track? Tell the DS system it was in EQ mode and give it the latitude....would that work? Does the base of the platform have to move at all then the scopes alt/az is?

[The Warthog]

I just put mine on a leash.... OH, a DOB! Sorry.

There are lots of designs around for motorised Dob platforms, and wedges for dobs. Sky and telescope last month or two months ago had an article on building a motorized, ball mounted, dob platform. Looks doable.

Here's a commercially available Dobsonian tracking system: http://www.telescopes.com/products/jims-mobile-jmi-nightrider-i-equatorial-platform-for-dobsonian-telescopes-46855.html

Most of these systems seem to take the Dob through part of an arc with the polar axis as the axis of the arc. The construction of all of them looks tearfully complex, although they all assure you that you can make them with simple carpentry tools. Right. Google "dobsonian equatorial tracking systems" and you will get quite a number of results.

[Jamie]

Just MHO CC but as soon as you alter the DOB platform it stops being a Dob right there and then.

[Ambermile]

Well, I don't know - installing GPS in a car doesn't stop it being a car you know

[Jamie]

Point taken Arthur but we are not talking cars here.

If you were to make so many changes to the build of a car that it became a van say "would you still consider it a car" i don't think so.

The whole point of a Dobsonian mount is that it is *the* simplest way of holding something to point upwards and look through.

Arthur

[Ambermile]

Well, it'd still get the wife to Tescos

[Jamie]

[The Warthog]

A Dob is, fundamentally, an alt-az mount. Many of us use alt-az mounts, and when we want to get tracking and go to functions, we usually buy an equatorial mount, or a fork-type goto mount. We don't mess about with out alt-az mounts to make them into equatorial mounts.

One of our members, I forget who, bought an equatorial mount for his Dob, put rings on the OTA, and put it on the mount. He was also able to use it as a Dob. For scopes of 10" or less, that seems to me to be the way to go.

I have been out lots of times and only bothered myself with the roughest polar alignment, as, if I'm not stopping to look at anything for long, I am just acquiring targets visually and with the finder scope - I might as well be using a Dob or an alt-az mount.

I think, if you really want to do photography, get an equatorially mounted scope.