Motor Drives

[AndrewSellek]

Hi all,

I'm looking at buying a new telescope on a budget of £300-500. I've come to the conclusion that a compromise on things such as GOTO, aperture etc somewhere will be necessary and I'm happy to sacrifice the GOTO - I know not everyone likes them anyway! However, I'd still like tracking.

I quite like the look of the Skywatcher 150P or 150PL which come with an EQ3-2 mount. You can buy motors for these mounts to enable tracking: either single axis (RA only) or dual axis (RA and Dec). I can't see when you'd need to track Declination though as while RA moves across the sky, Dec stays at the same level, so I'm lost for why you need a dual axis motor for tracking. Can anyone advise me or point out something obvious that I'm missing!

Thanks,

Andrew

[JamesF]

Having DEC motorised is handy if you're imaging or the scope suffers from vibration when you're moving the slow-mo controls.

If you want not to touch DEC at all you'll need very good polar alignment (and thus probably need the additional polar scope for the EQ3-2), but there's no reason for visual use that you couldn't motorise the RA axis and leave the DEC axis manual.

James

[Oddsocks]

For manual tracking you wouldn't need a dec motor as long as you achieve really good polar alignment, the object would stay centred.

But if you have poor or marginal polar alignment then the star will gradually move out of view and you would have to continually correct the dec axis.

Now it gets really complicated to try and work out how to move the mount to correct the drift, is it going to be a manual turn of the DEC fine hand control or release the clutch and push? or is going to be a press of the motor control button on the RA axis?

Same if you want to move to a new target, you have a motor control movement as well as a manual movement to make and it gets quite confusing managing the two operations.

To get a good enough polar alignment that will not drift the object in the dec axis using a high power eyepiece, or a camera, can take half an hour (using the drift method).

But a basic polar alignment and maybe a brief push of the motor control once a minute or so to keep the object centred only takes a minute or two.

For this reason, you would find it easier to have two motors and make all movements from the one motor control hand box.

So not essential, but a lot less stress!

William.

[Bizibilder]

My EQ5 has dual axis motors and is well polar aligned - the main advantage of the dec motor is for fine centering of your target or for moving around an extended object like the disc of the Sun or Moon. Very well worth having. Saves an awful lot of faffing about with slow motion knobs or clutches and allows you to sit with complete control of the scope and no vibrations being transmitted every time you touch the scope. For the same convenience I made myself a simple electronic focusser, now I dont touch the scope at all once set-up.

[AndrewSellek]

Thanks for all the useful advice. It only costs about an extra £10 so it seems to me that it is worth getting as it is less hassle. Am I right in saying then that it makes things easier to manually keep in view without proper tracking as I wouldn't expect the drives to be able to know how fast to track Dec, or does it generally have enough speed control that you can find something very close?

Andrew

[JamesF]

The motors only have three speeds, but it's not too hard to keep things in the field of view. Once I'd got my EQ3-2 moderately well polar aligned (just on the polar scope, no drift alignment or anything like that) I could keep a planet on a webcam sensor quite easily which is probably far more tricky than keeping it in view with an eyepiece.

James

[AndrewSellek]

Hi all, one last question:

Some people seem to doubt the quality of the mount and recommend an EQ5 instead. However, if I were aiming for an EQ5 then it's cheaper just to buy it with the 200P instead. What does anyone think about the comparative merits of the 150P + EQ3-2, 150P + EQ5 and 200P +EQ5?

Thanks,

Andrew

[AndrewSellek]

Also, how do these compare to a CG-4?

[Bizibilder]

If you are considering upgrading your kit then I would strongly suggest saving your pennies for something that will be future proof. Mounts are expensive but also about the most important part of your whole kit.

If you have a 150P then the EQ5 will be about the minimum adequate for visual work and maybe planetary/Lunar/Solar with a webcam (or DSLR for the Sun and Moon). If you want to go for a 200P then the HEQ5 is really the sensible minimum. Skywatcher have a habit of putting the largest scope they can on the smallest possible mount!! It keeps the overall package price down . If you want to be future proof (and save money in the long run) an HEQ5 is the minimum, even for visual.