Focuser Complete

The focuser is complete!

Actually it has been complete for a week, but I have been too busy enjoying the sky to post about it.

Turns out that I am not yet genius enough to design something to work first time just yet: during construction there were some improvisations I had to make with the original design that I will go through below.

Now that the focuser is working the difference in viewing quality is enormous. Being able to get the focus exactly (okay, not quite exactly) right without shaking the entire scope, as my friction fit focuser did, means that I can get sharp images without the telescope moving itself away from a target.

This will hopefully mean that I can finally start using the telescope to the limit of my optics. This is a welcome change from the limiting factor being something that I have done (or not done!).

The focuser

The focuser still needs a bit of touching up, at the moment the axle bar is a threaded rod which can lead to interesting interactions with the securing bolt and tends to shred the eyepiece holder. It is also 1mm too thin - I am probably going to take a quick trip to the hardware store soon to find a replacement and solve these issues.

Additionally, I managed to find a PVC plumbing fitting that fitted my required dimensions, but now is acting as a brilliant reflector of stray light into the eyepiece - I am going to have to paint it black at some point.

Finally my method of attaching the focuser to the scope can be seen above, it is not very pretty, but works well enough, for now. At some point in the future I may get around to improving the mounting mechanism.

Shot straight through the eyepiece slot. One of the things that did work were the four bearings which, due to a combination of brilliant datasheets from RS and the precision of the laser cutter, are precisely where they need to be.

The revised fastening mechanism. It seems to work quite well.

 One of the things that changed dramatically was the fastening mechanism. I turned out that I had not left enough room for the spring in my design. Looking around the web at other homemade focusers revealed that a surprising number simply used a bolt pressing on the axle to secure it. This also solves the longer term problem of the spring wearing out as the spring is now provided by the structure, it also saves me a wing nut for use in future projects.
I have epoxied a nut on the axle side of the back plate to hold the bolt, with a cannibalised section of the original pusher plate used to provide extra counter-torque on the nut. One of the problems that has arisen from the threaded rod being used as an axle is that it likes to move left to right (up-down in the photo above) when it is turned while under pressure from the bolt. This is usually fine, but can be a surprising pain.

Mirror holder - modified!

The final modification was probably the scariest, and is likely going to require more work in the future. Because the new focuser is about 3cm taller that my old loo-roll eyepiece holder, I needed to shorten the tube of the telescope by about this amount to move the focal point of the mirror. By pure chance, when I had originally put the tube together I had made the main spars out of two shorter sections of wood bolted together. This meant that shortening the tube was a simple matter of swapping out the shorter of the two pieces with an even shorter piece (as seen in the photo above). I was a bit sad to say goodbye to some of the last remaining original and reliable components of the telescope.
Unfortunately, because he tube shortening only occurred at one end, and the current setup does not allow me to slide the mount attachment point around, this has thrown the balance of the telescope off. Even with the proper mount, the front of the telescope really wants to drop. While I could revert to the old method of hanging a bag of rice from the mirror cell, I think that the longer term solution is going to be rebuilding the telescope tube assembly as this will also allow me to incorporate some of the lessons I have learn't (like having a movable pivot point).

One quick project down, how many more to go?