mad idea no 14704

[rowan46]

I have had so many mad ideas since starting this hobby. The problem with this one is it may actually be possible. a bigger problem however is I have no engineering knowledge, tools, or aptitude.

The brief. making my nexstar mount capable of imaging dso's.

solution putting another motor and encoder on the mount so that the scope is capable of rotating round the top of the mount at an angle 90 degrees to the angle it already does thus negating field rotation. any ideas

[brantuk]

It allready tracks in alt and az. What you need to track in a single plane (RA) is a wedge to tilt the whole thing at the correct angle to polar align. Here's an example of my dual fork setup:

http://stargazerslounge.com/members/brantuk-albums-telescopes-picture5733-cpc-4.html

[tonyh66]

You would have to get something custom engineered, sounds expensive. You'd be better off getting rid of the Alt/Az mount for an EQ.

Or sticking a wedge into the mount as suggested above

[steppenwolf]

Does the controller have an EQ mode though? If it doesn't then it will still track as though it is an Alt./Az mount so movement will be in RA and DEC and it will all go horribly wrong! On the other hand, if it does have an EQ mode then the wedge would be a great idea.

[brantuk]

Steves correct - here's the one Celestron used to do for the Nexstar series - you might find one second hand:

DISCONTINUED: Wedge, NexStar 6SE and 8SE (item #93658) / Tripods & Wedges / Accessories / Products / Celestron.com

(might need a software upgrade)

[rowan46]

Told you it was a mad idea. solving a problem that doesn't exist. onto mad idea 14705

[tonyh66]

Ok how about standing the entire tripod on a massive barn door tracker and not using the Alt/Az tracking at all......

[rowan46]

Ok how about standing the entire tripod on a massive barn door tracker and not using the Alt/Az tracking at all......

That's madder than my idea I like it

[Earl]

A good GEM is the best idea HEQ5 or better

[rowan46]

I know this earl but i need something portable that I can carry, trolleys make too much noise at 2 in the morning so i need to be able to walk it to my darker site My back garden is impossible but cheers for the advice

[JamesM]

Dave, one alternative is to make a wedge out of plywood but it would seem that the general consensus was certainly not to buy the 'real' one and this subject was discussed on here in January.

Here

Clear skies

James

[theodore]

Put it on an EQ wedge and disconnect the dec motor.

[Macavity]

Meade do a field de-rotator... At a nice price.

I did some tests with my Ioptron Alt-Az. I think DeepSkyStacker WAS doing the de-rotate in software OK-ishly? But I sense that the mount movement works best for visual observation, and is a tad "irregular" - Either in the hardware or software? Upshot was, I bought an HEQ5. More expense. <sigh>

I presume, the success of, adding a WEDGE. depends on the ability of the mount's Azimuth axis to function (friction-wise?) outside the horizontal plane. I understand that even e.g. "Giro" type mounts struggle...

[Mike Hawtin]

I've aready tried this idea out by removing the Dec axis from my CG-5 (a very simple operation)and bolting a mounting plate to it with three holes to suit the Nexstars tripod bolt holes. I was hoping to use it as a portable set up to image with my telephotos and a finderguider from a dark site. The thinking was that I could use the CG-5's polar scope to speed up alignment, this actually worked very nicely but in the end the whole idea failed due to the really poor autoguiding capability of the Nexstar mount, huge amounts of Dec backlash and only about +/- 6 arcsec in RA at best, not good enough really even for a 300mm telephoto.

[rowan46]

mad idea 14704b coming up then. It seems that a portable wedge is problematic for accurate setup and the weight necessary would stop the mount being portable. So If the spur gears were replaced by friction drive at the same ratio thus getting rid of the backlash. the tube could perhaps be made to rotate about its own axis. thus turning it into a field derotator and a portable imaging system is born

[FraserClarke]

. the tube could perhaps be made to rotate about its own axis.

There is no need to rotate the whole tube (it's rotationally symmetric after all) -- just rotate the camera.

[BinocularSky]

I'm pretty sure Mel Bartels's site has stuff for a DIY de-rotator (eyepiece/camera end) somewhere -- I think it's what Al Kelly used to use on the Danciger telescope (but is scalable to yours).

[Psychobilly]

Have a look at this...

http://stargazerslounge.com/imaging-discussion/125522-nexstar-6se-wedge.html#post1650307

there are some "plans" there for a 6SE wedge that I drew up for a member a few years ago... I used a "prototype" plywood wedge (19mm exterior ply) for a few months with the CPC800.. before making it in scrap ally plate and ultimately incorporating the design into a combined pier and wedge for the obs...

Compared to working in ALt/Az anything close will be an improvement.....

Peter...

[themos]

De-rotator is what the big boys use in the professional telescopes (which are alt-az).