[ATM] FW: two mirror folded newtonian

["McHatten, Shawn" <Shawn.McHatten@aliant.ca>]

Hi Folks
	Here is another link I was sent. Looks like a pretty good
implementation with decent baffling. Shane this is the link we were
looking for that goes along with the pics you sent me.

Thanks
Shawn

-----Original Message-----
From: Treur, Harro [mailto:harro.treur@waternet.nl] 
Sent: Friday, March 03, 2006 11:18 AM
To: McHatten, Shawn
Subject: RE: [ATM] two mirror folded newtonian


You can also contact  mike_fallwell@yahoo.com
He built an 18 inch long focus newtonian with tilted secondary. 
He has a website but I don't know the link to it. Try Google.

And another very good example is :
http://www.siderealtechnology.com/28inch/
the 28 inch of Dan Gray uses a tilted secondary with much succes.
I contacted him about this. See below:


If I ever built a new big telescope, I will certainly do a tilted
secondary.
 Good luck with your project

Harro Treur - Netherlands




>Treur, Harro wrote:
>  
> Hello Mr Gray
>  
> You have done a great job with the building of your progressive
> telescope and the website around it. My compliments!
>  
> I understood that the secondary is tilted in an unusual way. This is 
> very interesting and the perfect answer to a much asked
> question: "How can I lower the eyepieceheight?"
>  
> I would like to know the following:
> - Is optical fieldcorrection needed?
> - is this method restricted to a certain type of primary-mirror or
> f-ratio?
> - why is this method not used by the rest of the world?
>  
> best regards
> ****
> **Harro Treur**

Van: Dan Gray [mailto:grayarea@tms-usa.com] 
Verzonden: vrijdag 8 april 2005 15:21
Aan: Treur, Harro
Onderwerp: Re: question about the tilted secondary

They say every telescope is a compromise. This is so in a tilted 
secondary scope too.
The obvious advantage is lowered eyepiece height.
Another advantage is balance, and less strain on the scope frame.

To answer your questions, No, no correction is needed, your secondary 
just has to be flat.
No, it will work on any F-ratio.
It is not used for the following reasons I think:

1. Baffling has been a huge problem in the past.  I think I created a 
fairly cool solution, but baffling is still probably the hardest problem

to solve.
2. Straining you neck when looking near the zenith.
3. Danger of eyepieces falling out if not locked in properly (I have not

done this yet).
4. Use of slightly larger secondary blocks slighly more light than a 
conventional design, and causes a bit more diffraction
(I believe 4 to be fairly insignificant.

Dan Gray.


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