Brunn 300 f/16 Schiefspiegler

[Chriske]

Someone made such a scope in the past...?

Edited October 16, 2022 by Chriske
Changed title

[markse68]

is the idea only to avoid the central obstruction in a newt/cass? How much of an improvement would you actually get given all the extra reflective surfaces and collimation of them all?

Mark

[Chriske]

It is indeed our intention to make an unobstructed telescope.
Not only that but given the fact that sinds 1981 we've build 'a few' telescopes we wanted to build someting completely different and most of all a long focus telescope.
 Meaning this telescope will be used exclusively for Moon and planets. These extra reflection is no problem at all because our 'targets' are all rather bright...😀

[Chriske]

This is how it will loo like.

 

[Chriske]

Mirror 2 and 3 have the same ROC, and will be grinded together. The tool will be mirror 2 and the mirror(as we usually call it, so the concave one) will end up as mirror 3 in this system.
Because a few of us will be making the same Brunn we're planning to make these two mirrors(2+3) completely different. We will be using large blanks, large enough to cut these smaller mirrors out of it using  these...

It will save us lots of grinding and polishing work...😃

[Astrobits]

I made my own tube drills for cutting elliptical flats some 25+ years ago. I turned and bored ( at a local college workshop ) a steel bar to length and diameter and sent them to a diamond coater for tipping. The longest would cut 150mm depth of glass which allowed me to cut 4-5 blanks in one go. I found that where the cutter exited the glass there would be some chipping of the edge of the blank so the stack of glass sheets were stuck together with a special optical wax. This way only the top and bottom edges of the stack would be chipped, with the interior surfaces unblemished. Edge chipping would not occur when cutting circular blanks of course.

I still have those tube drills somewhere.

Nigel

[Chriske]

Circular blanks also do chip a little bit when the bit reaches the lower surface, but just a little bit.
To avoid it I a put a extra glass disk under the mirror. So doing the chipping is absolutely minimal and sometimes non existing. I need to press the two disks very firmly against each other.

Thanks anyway...👍

[davidc135]

Looking forward to following progress. It'll be interesting to compare performance compared to a, for instance, 10'' f6 Newtonian with minimal diagonal.

David

[Chriske]

Meanwhile busy drawing and we all decided to build a 300mm instead of a 250mm.
So David, to compare ours with your 300mm Newt... Start grinding...!😁

This is only a prototype on paper. Lots of meetings and discussing ahead.
But we will start grinding optics very soon.

The scope will be build in two parts. So whenever we decide to go and observe at an other location, it will be easier to transport.

Some more drawing to do...

 

[Chriske]

Next (drawing)step.Secondary cage and also a small shield just below the secondary mirror
Between the trusses we will add cross-connection to make it all very stiff.

 

 

 

[Chriske]

For maximum performance the eyepiece of this scope needs a tilt of 8.88°
So this what it will look like.

On the left,
Focuser barrel,   8.88° correcting device,   2" to 1"1/4 adapter, and on top the eyepiece.

Every eyepiece needs it's own 8.88° adapter, except for the par-focal eyepieces of course.

[Chriske]

Crayford part of the focuser.
It has a dual speed knob. The two bolts are for adjusting tension on the barrel.

 

[Chriske]

This exploded view shows how it looks like inside the Crayford.
In the white part there's a ball bearing that fits over the brass rod.

[Chriske]

Maybe we'll go this way.
Two poullies and a timing belt. Reduction 1:4

[Chriske]

One more modification, added a belt tensioner(yellow)

About 25mm long

 

 

Bolt (M3) on the right is pivotpoint of the tensioner
Centre bolt is the pusher (brass)
Left bolt is the tensioning bolt