EQ Tracking with a DOB??

[Screwdriverone (Chris)]

Hi All,

Forgive me for this question in advance as I think I know the answer but I thought I would ask anyway:

Is it possible to make a dobsonian telescope "track" like an EQ mount by elevating its base to the angle of your latitude and then use the Azimuth bearings only?

What I am suggesting is a wedge type box that props up the base to e.g. 35 degrees and allows "tracking" for longer on Planets etc.

The reason I ask is that I have seen some Meade ETX and Ioptron alt/az mounts that have a side slider that jacks up the mount to EQ height by tipping it over and then the mount behaves like an EQ mount. Is there something else going on in the electronics of the GOTO mount here where the computer senses the tilt somehow and automatically corrects itself as it tracks?

Therefore, the question re the dob above.

Thanks for contemplating this for me, any answers would be helpful.

Cheers

Chris

[prova]

Hi there, here is one option I know of -

http://www.roundtableplatforms.com/default.php

[Screwdriverone (Chris)]

Thanks Prova,

That option seems to be a clock driven power turntable, not quite what I was asking, think tilt to 35 degrees then spin manually on azimuth bearings only. Obviously this then needs the tube to be "locked down" in altitude to remain stable.

Chris

[tnott]

I think you would have problems with the balance. A dobsonian is held in place by gravity, so putting it on a platform tilted at 35 deg might make the whole scope fall over, change the pressure on the teflon pads or make the alt. bearings pop out of the rocker box for example.

The equatorial platform solution is possible to make yourself or can be purchased from a variety of makers.

[AlexN]

Yeah, the eq platform as linked in above posts rotates the base, so all you have to take care of is the altitude.

The ETX and Ioptron setups electronicly control altitude and azimuth.

With the wedge or tilting slidey thinggo they have, the azimuth axis is lined up with the SCP so as it rotates around in AZ, you get the correct field rotation on the scope. the altitude of the scope is automatically adjusted aswell...

You can get GOTO systems for dob's but they are not eq, and not suitable for photography.. they do offer tracking (some do anyway.. Search the forums for bartelized dobs) but, these systems can not compensate for field rotation... I have no doubt with the right tools and a very technical mind, you could probably do it.. but not cheaper than you could buy a HEQ5 Pro or EQ6 Pro...

[Screwdriverone (Chris)]

Hmmm, thanks Alex, that pretty much confirmed my theory then, it was the image rotation that I was missing, I thought the similar "tilt" mode of the Alt/Az mounts might be able to be reproduced with the DOB to allow longer tracking only on the AZ axis, but it seems its a bit of a pipe dream.

I wasnt trying to replace the idea of an EQ5-EQ6 mount (by the way Andrews now has the EQ6 for $1499) with a DOB tube on board, but thought if I ever buy a dob, and get the "you know whats" with having to nudge it constantly, that maybe there is a fudged method of getting more viewing time when visually tracking something.

Thanks for the replies everyone.

Chris

[AlexN]

Mike had very very good results imaging Jupiter/Saturn through his 10" dob and one of those EQ platforms.. I'll say, doing it the way I do it is frustrating to say the very least. and every single mm more focal length only adds to the frustration... getting jupiter in the FOV without a barlow is simple.. doing it with a 3x barlow and extention is pushing my buttons all the wrong ways.

[rmcpb (Rob)]

You are talking about a dob wedge and I had a play with this for a while BUT it took lots of rebuilding of the base to get it to work well.

Have a look at this item on CN.

Cheers