Skywatcher Explorer 130P autofocuser

[ballme1]

I am trying to find out if there is an autofocuser that will fit a SW 130P GOTO telescope, or if not, one that can be modified to fit ?

[discardedastro]

Depends what you want to achieve and what you're using it for!

Autofocus is a bit of a misnomer, usually, since the scope/focuser itself has no way to tell what good looks like. What you need to do is first motorize the focuser - Skywatcher sell (rather confusingly named) a DC Autofocus motor which should fit, from memory, the 130P. This isn't a great motor, but the 130P's focuser isn't terribly fantastic anyway, so it'll be alright. With just the motor you can achieve pretty precise focus control by hand and eye using the supplied controller, and that's a great start if you're just doing visual observing - it will make it easier to focus as you won't be bashing the tube, and it'll give you more control than the single-speed focus knobs will. Pair it with a cheap Bahtinov mask and you'll be able to get superb focus for observing.

To achieve auto focus for imaging, you need to involve a computer and a camera. There are various bits of autofocus software out there, mostly commercial; INDI is free/open source and I think has autofocusing support, but not sure how good it is. However, the 130P focuser and DC autofocus motor isn't very repeatable - something that's a key feature for accurate computer autofocus for imaging. So if you really want to achieve good autofocus you're likely going to want to swap the focuser and use a stepper motor controller. That's a huge step up in cost. There are some DIY approaches to this that might be worth exploring, and having said all the above I manage OK with the Hitecastro DC Focus and the Skywatcher motor on my 200PDS.

[ballme1]

I am trying to set up my scope so that I can have the scope outside but with me inside the house using a wi fi adapter to control the mount (wirelessly) from my laptop. In addition I will be adding a webcam to the eyepiece (with extended lead) with the other end connected to my laptop.

To finish this set up I wanted to add an autofocuser (with extended lead) so that I can also focus inside the house.

I was not sure if the Skywatcher autofocus motor will fit my 130P as all adverts do not show this fitting my 130P ?

This is what the adverts mention -  

Can be used with the following telescopes - as long as the focus knobs have the centre screw: 

Evostar models 90/102/120/150

Startravel models 80/102/120/150

Skyliner models 150/200/250/300 

Explorer models 150/200/250/300

[wimvb]

I have used the sw "autofocus" dc motor focus together with my 150PDS (with Crayford focuser) and INDI. Ekos, the INDI client, has a very good autofocus routine. Unfortunately, the dc motor has quite a bit of backlash in its gears. You will also need to replace the motor hand controller with a computer link. I made mine with an Arduino.

Hope this helps

[ballme1]

Thanks for the information. I was only intending to use the autofocuser with the handset on an extended lead, rather than direct from the laptop (although that sounds a great idea, but too technical/costly for me, as a beginner)

Still not sure if the Skywatcher Autofocuser will fit my scope as the focus controls seem different to your 150 ? See attached photo

If it needs modifying, does anyone know what I will need to do to make this work with the Skywatcher autofocuser ?

 

[discardedastro]

Fairly sure you'll be fine attaching it - the kit includes two brackets, one for the DS versions (though I found some filing/cutting of the bracket was required to let me adjust the focuser with the bracket fitted) and one smaller one for the regular versions that looks like it'd fit that.

[wimvb]

As @discardedastro wrote, the smaller bracket should fit. Remove one of the knobs and attach the motor first. Then attach the bracket to the base of the focuser and to the motor.

If you want a longer cable between the hc and motor, any RJ10 cable will do. (Although I found the one showing in my pictures a bit heavy, to be honest.) Computer control is only necessary if you want to automate your setup for imaging. But do keep an extra 9 V battery handy in cold weather.

[ballme1]

Thanks all for the info. Just the issue of removing the knob now, as these are not held with grub screws, but seem to be glued on !!  Just worried that I am going to damage the focusing knob and shaft.

[wimvb]

I don't have this scope, but maybe the focus knobs have a small cover which hides a nut. Or the knobs can be screwed off?? If you hold both knobs and gently try to turn them counter clockwise, one may loosen. Just don't force anything.

[ashortfallofgravitas]

Avoid a DC focuser if you can, get a stepper one.  Also, NINA has a great autofocus tool.

[discardedastro]

Stepper focusers are great, but aren't available "out of the box" for the Skywatcher focusers. You'd need to swap the focuser out or build your own, and frankly it'd be a bit mad to put an expensive focuser with stepper on a 130P! Making your own is doable, but you need to make a bracket, driver, controller, and you still are at the mercy of your focusers' quality as to how repeatable a focus you'll get. I've dismantled my 200PDS focuser entirely, flattened the flat on the drawtube to as close to perfect as I can get, tensioned/balanced the pressure plate, and it's still not fantastic.

[adyj1]

On 06/02/2019 at 10:05, ballme1 said:

Thanks all for the info. Just the issue of removing the knob now, as these are not held with grub screws, but seem to be glued on !!  Just worried that I am going to damage the focusing knob and shaft.

This scope's baby brother, the 1145p has knobs which screw off - no grub screws used. 

I was in the same position as you, but once I realised there were no grub screws to be found, I took upon the task of unscrewing them. They did come undone, but not without a 'very firm' amount of force - more than you might feel comfortable with, but not enough to bend anything... 

It *might* not be the same for the 130P, but I'd suggest a little bit more force... 

Ady

[wimvb]

11 hours ago, adyj1 said:

I'd suggest a little bit more force...

I didn't want to go there and be the cause of a mishap. But you're right of course, it usually takes quite a bit of force to loosen knobs like these. I don't know if a hot air gun will help. But it may damage the plastic/rubber ring on the knob.

[adyj1]

2 hours ago, wimvb said:

I didn't want to go there and be the cause of a mishap. But you're right of course, it usually takes quite a bit of force to loosen knobs like these. I don't know if a hot air gun will help. But it may damage the plastic/rubber ring on the knob.

Hot air is another good idea. 

I know what you mean about not suggesting potentially damaging advice, but for me that was the only thing that would work. 

Read the warnings, and try at your own risk... 

Ady 

[ballme1]

It was so tight that I did not risk it.

In the end I built my own auto focuser using an old radio control servo/belt and a hand held unit, with just a hard foam wheel over the existing focusing knob. Works a treat and I can go back to my existing set up if needed !!