Motorised focuser for NexStar 4SE

[Baz6170]

Hi all

I've got a NexStar 4SE that I really want a motorised focuser for, but looking around the net hasn't really provided any answers. I've taken a pic of the standard focuser as it stands on the scope, which is visible below.

From looking at the pic, do you think it'd be possible to buy/make some kind of bracket that could be attached to the scope using the same mounting points as the finderscope (ie fit between the scope and the finderscope), where the bracket could then hold an off-the-shelf remote controlled motor drive which would turn the focuser via a drivebelt?

I really want to find a solution for this as I'm currently using the scope to image planets with a SPC900 and even though I use a bahtinov mask, getting fine focus with the 4SE is pretty tough due to the basic nature of the focus mechanism.

Thanks all, here's hoping someone out there can help and point me in the right direction re parts etc!

Baz

[knobby]

In the mean time you could try a peg on the focuser, at 90 degrees... If that makes sense

[mikehab]

In the mean time you could try a peg on the focuser, at 90 degrees... If that makes sense

I've heard of people using a clothes-peg to provide more 'fine-tune' tweaking of the focus knob - does that really work in practice or is it just an April-fool / gimmick?

[Demonperformer]

Yes, it works. The principle is that it effectively turns the focussing knob into one with a larger diameter and therefore circumference. Therefore, if you can move the circumference by the same amount, it converts into a smaller angle, and therefore finer tuning.

HTH

[AllanJ]

I use a 22mm pipe collar to extend the focuser diameter. Works a treat.

PlumbSure Pipe Collars White For 22mm Pipe 5Pk £3.49

(a 5 pack may seem a lot, but the plastic lugs can break)

Allan

B&Q site

http://www.diy.com/n...?skuId=11988303

[Baz6170]

Thanks for the advice all, I'll give Allan's collar solution a go, see how I get on. I've been doing a bit of research on the motorised option and if I go ahead with it at a later date I think I'll get the Skywatcher Auto Focuser and adapt that. The pipe collar could come in useful as if I make the circumference grippy, the motor could drive the focuser directly ie wheel to wheel rather than me having to set up a drive belt solution. Thanks all for your help!

[mikehab]

I'm having similar problems focussing the 4SE when trying to image planets via webcam - the real problem for me is that just the slightest touch of the scope/focus knob causes the image to jump around all over the place, so it's virtually impossible to focus the image as you can't actually see a stable image. Even the clothes-peg or pipe-collar options above require you to touch the scope/focus knob - so I don't think this would help much with the violent shaking that ensues. Hence I too am looking for a motorised solution that might help with this... plus of course it would also have the added benefit of my being able to control the whole scope completely remotely from a nice warm room

As per original poster, I've also tried focussing on a star first using a bahtinov mask, and then slewing to the planet, but I always find that the planet isn't in focus and needs re-focussing... is this normal to have such a focus difference between planets and stars? I know the planets are a heck of a lot closer than the stars ... but even so, I would have thought that difference wouldn't have been 'astronomical' (sic) in terms of focussing close to infinity?

Thanks,

Mike

[mikehab]

I just stumbled across this article which explains how to create a "battery free motorized focusser"... some interesting lateral thinking there... just need to work out the physical logistics of how to attach one of the servos to the focus knob on the 4SE ... but I do quite like the idea .. it's still 'manual' adjusting but without having to touch the focus knob itself... hmmm...

http://homepage.ntlworld.com/telescope/Projects/ElectricFocuser.htm

[fluffkat]

I know this is an older post however I have made a Bracket for the Nexstar 4se which can be 3d printed. The project is based upon Ardufocus and is fully ASCOM compatible and controlled over usb. More details are on the project page:

 

https://www.thingiverse.com/thing:3144339

 

Hope this helps someone out!