Herschel telescope on a stick

[Chriske]

Made a small telescope for our youngsters. At the moment it's only a 'paper version', Just started printing the parts.
It is a 75mm f/20, So basically to watch the Moon and maybe a few planets.
The pole is 25mm thick aluminium.
Main issue was to make this little thing as cheap as possible.
The mirror I made for this scope was a 250mm f/6 spherical. After final polishing I used a 75mm diamond coring bit to drill out  7 smaller mirrors.
I chose this f/value because it has a rather good spotdiagram. The central spot fits exactly in the airydisk(somewhat smaller in fact, not absolutely perfect), but good enough imo.

The focuser is of own design. There's no focusing knob. Focusing will be done by pushing the eyepiece barrel very slowly up or down. While moving up or down I need to rotate that barrel very slowly to have a smooth action. I did something similar in the past and it works very well.

To tune the scope the very first time you need to lay the scope on a flat surface. All three parts do have a plane at the side. Pushing the scope firmly to the flat surface you need to fasten these three parts(mirror holder, bearing part and the focusing unit) to the main pole. Next you need to collimate the optics.

This is the plane at the primary mirror holder.

 

Focusing unit and secondary mirror combined in one part.

To hold the eyepiece barrel in place there's a spring involved

 

Focusing unit,  friction between the unit and focusing barrel should hold the eyepiece in place.
Cost to print this focuser : 0.36€

Scope seen from the business end ...

[Chriske]

Collimation of the primary mirror is a classic push-pull system.
Secondary mirror is a completely other system. There was not enough room for a push-pull so came up with something completely different. I've actually used the classical push-pull principal, but in completely different way.

This is the scope with it's top cover on.

Top cover removed and the scope tilted to see inside the collimation part.
All collimation holes, side by side.

 

 

Seen from the other side.
The red parts is mounted in the big telescope unit and rotates in only one direction. It is secured with one push-pull set of bolts
In the lower right drawing you see two parts. At the far right in the 'assembly2 drawing' you'll see somewhat smaller hole. That hole allows the blue part to rotate just a little bit. The rotation in the drawing is strongly exaggerated of course. The rotation of that  blue part is done with the two push-pull bolts at the far left. That central hole there has noting to do with that last collimation.
For that last collimation I only needed one set of push-pull now that I come to think of it.

 

 

The difference between the classical collimation system is that I tune in only 2 directions instead of three.
And again I could remove on set of holes in the blue part.