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Guide to making an Auto Focuser


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Hi all,

Some of you may remember me a while back saying I was going to have a go at making an auto focuser. Well I have finally done it, well it got built a while ago but my 4 month old son decided he was more important and took most of my time :)

I took a lot of pictures during the build as pictures speak better than words. I wasn't sure how many pics I an upload here so I created a page detailing how to build it.

DIY Focuser

Hope this can be of some use to someone.


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May I ask why you kept the pcb from the servo ?

I got rid altogether and wired the batteries-pot-DPDT-phono socket then cable to the servo,-phono-servo

I use 2x AA's

Works very well as is tho but clearly you know your stuff ( unlike myself) and if I can improve it I'd like to

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There is no reason to keep the board, I was just too lazy to desolder the motor. Also I wanted the phono connector seperate to the servo. This way when unplugging and plugging in you are not putting strain on the mont the servo sits on.

For the batteries I found with 9V I had greater range on the pot before the voltage dropped off. See the following link for a pot calculator a tthe bottom of the page Potentiometer greater range on the pot means finer adjustment.

I don't know about knowing my stuff it's been over 13 years since I was a sparky :)

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I think I know how to attatch it to the scope and for linking the servo to the focus knob well....... I did wonder if a tractor tred from lego would work. Something to experiment with this weekend. Once I have it figured out I will update the web page, and include pics.

As for the 9V battery being too fast, it could be because I am using all the gears to slow the servo down as well as the pot. I did connect it to the motor direct but yes it was too fast.

Edited by Abernus
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  • 2 weeks later...

I have finally had time to get back to this one and look at the mount issue. I didn't want to drill any holes in the OTA, so was looking at other way to mount it. Good news is I have done it

Head on over to the guide and scroll to the bottom of the page to see the pics and write up.

It works a treat :)

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That's an excellent really well presented 'how-to'. I used the same approach last year but I'm too ashamed to display my terrible soldering to the world. I ended up using using some sticky pads to mount the servo to the back of a 127mm SW Mak. Unfortunately I haven't worked out how to connect the two together - things either slip or bind. For the voltage I'm using 4 x 1.5 AA which work OK. Thumbs up for a first rate guide

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