DIY Helical Focuser

[samtheeagle]

A couple of weekends back I finally got around to making a simple focuser for my 50mm finder/guide scope. I did this because I found it VERY imprecise to simply slide the camera back and forth into the extension tube... I'm going to use a bundle of pictures here, I hope that they'll convey what I did clearly enough, but if not fire away with questions

The key component to this project was a plumbing widget from Wickes, which cost a grand total of 1.97! It was a step down adaptor from one pipe size to another... I just took along my 1.25" extension tube and found one that was pretty close. Here's the item I purchased: Wickes *–*Heating, Plumbing & Fires*–*Waste*–*Waste Fittings*–*Reducer Universal which converts from 40mm down to 32mm.

Let's start at the end, with the finished focuser:

Here are the constituent parts:

These next two pictures show the main part that requires fabrication. This is the main focus "shaft", which has a 1.25" nose piece adaptor embedded in it. This is the part that will move in and out as you rotate the focus knob.

To make this I cut the threaded part from the 32mm end of the adaptor before the pipe increased it's size up to 40mm... Then I affixed an appropriate length of 1.5 inch plastic pipe, which needs to be bored out a small amount to get it to fit over the exterior of the metal extension tube.

Next I needed to cap off the end of the tube so that I could affix the 1.25" nose piece. Carefully make a hole in the centre for it, so that it'll slide into the metal extension tube when in place.

I used no more nails for all these joins, and thus far everything seems secure enough.

This final picture shows the parts in an almost assembled state. I used the rubber washer part from inside the adaptor as a handy stop, to prevent the focuser "wheel" moving down the extension tube instead of pushing the shaft out. Of course this doesn't help when racking the focuser back in, for that you just have to apply an appropriate amount of pressure down against the stop. If you don't the wheel will just move up the metal tube instead of pulling the shaft back in.

I hope that kind of made some sense, it's a rather brief run down of the fabrication... Like I said, fire away with questions if something doesn't add up! It's a very cheap and cheerful solution, but it bloomin works!

[martor]

Great work! How much travel do you get with the focuser (end stop to end stop)?

[Merlin66]

Nice piece of DIY!

I thought the same for a spectroscope but with the Canon 350 hanging off the back, I ended up with the Baader Helical focuser from TS.

For lightweight webcams etc your solution will work well.

[samtheeagle]

Martor, I think it gives about 10mm of travel, I can measure more accurately tonight if you want? Basically the amount of travel is defined by the depth of the threaded parts and how long a slot you make for the thumbscrew to go through. You might be able to get slightly more travel, but I didn't want the threads coming apart if I racked the focuser back too much...

I already had a pretty good idea of the focus point for the web cam when slotted into the extension tube, so I just made sure that the middle of the focuser travel was at about that point. Now I can tweak it ~5mm either side to get a nice sharp focus

[beamish]

Great use of resources, both material and cerebral !!

[steppenwolf]

Very good indeed - a good project for a lightweight camera

[samtheeagle]

Thanks! It's amazing what weeks of cloudy horrible weather can encourage eh?

[adamsp123]

Brilliant bit of DIY!

[Digz]

I plan to make my own finder guider and whilst seraching the forum came across this. Looks like a nice piece of DIY, but Im struggling to follow it, any chance of a photo of the setup in use?

Cheers

[samtheeagle]

Yikes! I'll see what I can do, but I've since retired this from service... It might be in a box somehwere, I'll see if I can dig it out. But for now I'll try and explain how it's used...

If you refer to the first picture in the original post you can see the whole thing assembled. The silver part on the right is slotted into to the 50mm finder, where the EP would normally be, and the web cam is affixed to the threaded section protruding from the left handside. Then when you rotate the central part it pushes or pulls the part on the left that has the camera fixed to it, thus adjusting the focus... Nothing particularly fancy or clever... Hope that helps?

[Digz]

I think that answers the question I had, thanks for explaining to me