RE: [ATM] Movement of the Secondary mirror in a Newtonian system

["Treur, Harro" <H.Treur@wlb.amsterdam.nl>]

Hello Russell,
If I understand correctly, I think you have the same question that I had a
few months ago.
Have a look at the 28 inch telescope of Dan Gray.
http://www.siderealtechnology.com/28inch/
He uses a tilted secondary (I think about 30 degrees instead of 45 degrees.)
This secondary is a circle instead of elliptical.

I could not imagine this would work, so asked him a few questions about this
Offlist, which he answered very clearly.
Dan's experience is that the angle of the secondary does not matter!
The eyepiece height is lowered by about 0,50 metre, which is a wonderful
achievement
 

The only disadvantages are:
1 - baffling the secondary is difficult. But Dan managed to get a proper
baffling by using exotical baffle structures upon the spider.
2 - When looking at zenith, there is the risk of the eyepiece falling out of
the focusser.
3 - When looking at zenith you will have to strain your neck a bit.
4 - the obstruction is slightly more, but not noticable visually.
 
Hope to have given you the answer on your question.

Good luck

Harro Treur








> -----Oorspronkelijk bericht-----
> Van: Russell Jocoy [mailto:russjocoy@hotmail.com] 
> Verzonden: woensdag 3 augustus 2005 1:59
> Aan: atm@atmlist.net
> Onderwerp: [ATM] Movement of the Secondary mirror in a 
> Newtonian system
> 
> 
> 
> 
>     To all,
> 
>                 I am most likely treading over old found 
> facts of my insight 
> , or questioning a
>     rock hard system.. Basically a brain fart...
>           The basic idea of a Newtonian, or "dobsonian" scope 
> .. is that the 
> primary mirror reflects
>     incomming light to the secondary mirror (which is flat as 
> can be) and" 
> that" secondary mirror
>     being positioned at a 45 degree angle to the scope (or 
> light plane) 
> sends light to the eyepiece
>      through the side of the tube..
>               What if the secondary mirror was off axis from 
> 45 degree to  
> say 40 degrees. Would this
>         not aim the focuser back towards the primary mirror 
> (or to the 
> ground as in most scopes?)
>             What if you went to 35 degrees? I understand that 
> the secondary 
> would have to have it's
>           long axis measure adjusted , but does this work , optically?
>                           Rethinking something that has 
> already been done ,  
> I'm sure..
>     PS.. This would cut down on neck craining on top of the ladder..
>                                                         Russ Jocoy
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 
> 
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> ATM mailing list http://www.atmlist.net/
> 

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