250mm f/10 Stevick-Paul

[Chriske]

Hi,

Busy drawing/building a scope my dear friend Marc was 'in love' with but never found the time to actually built it. Marc died only two weeks ago.
It is a rather odd looking scope, but is optically the best ever designed.
Looking at the spot diagram, no other telescope will ever beat this telescope type.
Anyway, this is what it will look like when it is finished. This scope is 1.7m long.

The large arrows is the COG(according to Autodesk-Inventor)

Taking a way one side panel, it looks like this

 

[Dr_Ju_ju]

Not seen the design, so I take it that using flat mirrors set at the appropriate angles would even out any chromatic aberrations ??

[johninderby]

Have read a lot of threads on CN on the design but not many have actually gone on built one. Think the complexity puts them off. 

Will be interested to see how you get on with the project.

Edited December 31, 2019 by johninderby

[Chriske]

Hey Julian,

There's no lens involved, so there's no chromatic aberration present.
There's only one flat + 2 concave and 1 convex mirror.
You couldn't possibly see that of course, my mistake, I should have mentioned more about the configuration, sorry again.

[Chriske]

11 minutes ago, johninderby said:

Think the complexity puts them off.

Think so too.
Been pushing glass for over 35 years now, so I like a challenge...😁

[Gina]

I reckon if anyone can do it Chris, you can!

[lukebl]

Interesting but surely, with four mirrors to deal with, collimation would be an absolute nightmare?

[Gina]

That's a thought.

[johninderby]

Considering this is an old design dating back to 1935 surprising that there are so few of them around. 

[Peter Drew]

26 minutes ago, lukebl said:

Interesting but surely, with four mirrors to deal with, collimation would be an absolute nightmare?

It would have been pre laser collimation.    😀

 

 

[Mick J]

Go for it Chris,  what a good idea and great way to remember your friend Marc.

[lukebl]

58 minutes ago, Peter Drew said:

It would have been pre laser collimation.    😀

Is that good or bad?

[Chriske]

1 hour ago, Mick J said:

Go for it Chris,  what a good idea and great way to remember your friend Marc.

That's the idea Luke...

[Chriske]

2 hours ago, lukebl said:

Interesting but surely, with four mirrors to deal with, collimation would be an absolute nightmare?

Not only standard collimation will be a nightmare Luke.
First thing to do is arranging the mirror so they're at the correct distance, within a millimetre or less. That's is a very important issue.
So all mirrors should not only be adjustable with their three 'standard' bolts but on top of it also moveable away from each other(or nearer)

[Peter Drew]

With spacings being critical I would expect that focal lengths of imaging surfaces to be equally precise.     🤔

[Gina]

Maybe I won't build one then 🤣

[Chriske]

9 minutes ago, Peter Drew said:

With spacings being critical I would expect that focal lengths of imaging surfaces to be equally precise.     🤔

Indeed.!
That is why for this kind of precise work I always use a 120mm diameter spherometer combined with dial gauge capable of measuring 1/1000 of a millimetre.
Still during polishing constant monitoring all FL is required.

[wimvb]

On 31/12/2019 at 22:04, Chriske said:

Indeed.!
That is why for this kind of precise work I always use a 120mm diameter spherometer combined with dial gauge capable of measuring 1/1000 of a millimetre.
Still during polishing constant monitoring all FL is required.

So you won't be building this in wood then, as the drawings suggest. Carbon fiber? What will the fl be? 

[Chriske]

Comparing with other telescope types, when all is correct : FL, distances between mirrors and angles, nothing can beat a Stevick-Paul.
This ray traces reveals it all :
The small circle in the centre is the Airydisk.
FOV is always 0.5°

Original Stevick-Paul

Because of its length, almost 2.5meter, I have chosen to use the folded version.
Not perfect but close.

Compare it with a Newt, even at F/10 it has severe coma.

A Original Cassagrain

Dahl-Kirkham

 

 

 

[wimvb]

Impressive. I'll be looking forward to the progress. 

[Peter Drew]

Whilst acknowledging the superiority of the Stevik-Paul system, I'm surprised that the plots look so bad for the Newtonian and the Dall-Kirkham. I have a 12" F8.5 Newt and 12" F20 D-K and don't notice coma over a 0.5 degree field visually.   🤔

[Chriske]

3 minutes ago, Peter Drew said:

Whilst acknowledging the superiority of the Stevik-Paul system, I'm surprised that the plots look so bad for the Newtonian and the Dall-Kirkham. I have a 12" F8.5 Newt and 12" F20 D-K and don't notice coma over a 0.5 degree field visually.   🤔

Take a picture with it an you'll see. A starfield will reveal that typical Newt error
Visually you should not see it as in the ray trace.
But there's a tool to get rid of that coma, coma-correctors.

This is the ray trace is of your Newt Peter.

Most probably there's corrector somewhere in that Dahl-Kirkham of yours.
Without that  corrector it would look like this :
I know it's a 10" f/18, but the longer these DK are made the worse it gets.

[Peter Drew]

My two 12" Dall-Kirkhams and 10" Dall-Kirkham-Dall are self built, the DK's contain no correctors, the DKD has an erector transfer system.  Looks like visual use is, thankfully, much more tolerant of aberrations  than imaging.    😀 

[Chriske]

11 hours ago, Peter Drew said:

Looks like visual use is, thankfully, much more tolerant of aberrations  than imaging.    😀 

Indeed.
At the very centre these DK's are very good..!

[Chriske]

Together with my son Steven busy grinding the optics for this telescope.