Electric Focuser

Hi all,

Is there anyone useing Electric Focuser with their scope?
Would like info on this subject as I am thinking of purchasing same.

I find that I cannot focus precisely with my ETX125EC as the image drifts in & out of focus continueously.

This may be down to the fact of cooling down time.

I think its 20-30mins for very inch of focal length.
Thats a long time by any standard.

In our temperate climate the scope would have too be left out for great lenght of time before viewing begins. Hope the rain holds off.

Then again having a dome or some kind of outside observatory would`nt be a bad idea.

I will leave it with you.

Many thanks in advance.

Regards,

Yagis.

Hi Yagis,

Sounds like image shift. One way of checking for sure is do the following:
-Focus the image
-Turn the focus two revolutions clockwise. Note which way the image has shifted.
-Refocus the image.
-Turn the focus know two revolutions anti-clockwise. Again note the direction.
Ideally try this experiment on Jupiter. Try and estimate how many Jupiter diameters the image shift is. This will indicate how serious or minor the problem is.
If the image has shifted in opposite directions in these two tests then you have what's called image shift. Try this test and let us know the result.
I had a similar issue with my scope. Electric focusers are very expensive. Instead I invested in a Borg non-rotating helical focuser and 1.25" adapter. I'm extremely pleased with it - so much so that I'd recommend every SCT owner to invest in one even if you don't have an issue with image shift. It allows extremely smooth and accurate fine focusing - far superior to the standard focuser. I consider this the single best accessory with my scope.

Michael

"I find that I cannot focus precisely with my ETX125EC as the image drifts in & out of focus continueously:

I hope it is image shift otherwise its mirror flop, which is a much more pain in the head the image shift, of course presuming what you are witnessing is not just changes in the seeing ??

Does the focus change without you turning the focus dial ? i.e. by itself ?? especially if you move the tube.

As for 20-30 mins for every inch of focal length, that doesnt sound right to me, otherwise it would be 60hrs for my scope. Usually 2-3 hours is good enough for most scopes, just doent let it get cought in the rain.

Hi,

I've a JMI motofocus for my scope.

With my scope, Meade LXD55 10", at high magnification even the slightest vibration can cause the image to bounce all over the place. And turning the focuser would cause the image to go out of view! So I got the electronic focuser so that I could focus without having to touch the scope and minimise the vibrations.

Btw my scope takes about 3 hours to cool down properly.

Cheers,
~Al

Hi Albert,
I didnt think that the rack and pinion focuser would move the object out of the field of view in the LXD, do you mean that the vibration is enough to make it wobble out of the field of view or are you describing some sort of shift in the focuser??

I use the old meade electronic focuser (no good for Lx90s or LXD scopes)which moves the mirror, I had contemplated getting a micro focuser, but thankfully the image shift I get is about a saturn diameter (+ rings), so with a barlow I just about manage to keep saturn on the chip of the toucam pro, mind you I cant image at such a high mag as saturn fills half the field of view, I only use it on Venus.

Hi Albert,
I didnt think that the rack and pinion focuser would move the object out of the field of view in the LXD, do you mean that the vibration is enough to make it wobble out of the field of view or are you describing some sort of shift in the focuser??

The focuser is fine.

Its a schmidt newtonian so when you touch the focuser you are moving something about 50cm away from the mount. At high magnification that little bit of force you use to turn the focuser can cause the image to wobble in the field of view and makes focusing really annoying and hard. And the mount isnt up to handling the scope at high magnification like that really, though anti-vibration pads and the focuser have almost completely removed my vibration problems.

Cheers,
~Al