Re: [ATM] Looking for information on a telescope design

[David Weinshenker <daze39@earthlink.net>]

oh diepoes wrote:
> 
> Other option: Folded Newton:
> Parabolic primary, flat circular secondary and elliptical flat tertiary.
> http://johanneswilm.org/mike/telescope/

The 2-mirror folded design on that page looks interesting also - a
clever means of getting the eyepiece nearer the aft end without
secondary magnification or inordinate obstruction!

-dave w


> 
> Rgrd,
> 
> Yigal
> 
> 2007/8/28, dave w <daze39@earthlink.net>:
> > Steve Chambers wrote:
> >
> > > Hello,
> > >
> > > I am thinking about building a large (~30") scope.  I remember reading
> > > about a nice design that kept the eyepiece at a comfortable height.  The
> > > scope looked like a large Dob but observing was done through a refractor
> > > near the base.  The light cone was somehow folded and collimated before
> > > entering the refractor.  Does anyone know what I am talking about?  The
> > > name of the design and a link would be great.
> >
> >
> > Sounds like you're thinking of something like what is often called the
> > "Nasmyth" configuration: it's basically a "Cassegrain", with a convex
> > secondary mirror near the primary focus that partially diverges the
> > focused beam and reflects it back toward the primary, but instead of
> > passing through a perforation in the primary, it is reflected, by
> > a small diagonal mirror, to an eyepiece location at the side of the
> > telescope near the primary. Nasmyth's original telescope of this type
> > passed the optical path through one of the elevation bearing shafts -
> > his mount had a seat mounted on the azimuth turntable and a pair of
> > handwheels within easy reach, with which he could aim the telescope
> > at any point in the sky while looking through an eyepiece that
> > remained stationary with respect to the seat.
> >
> > This layout could be applied to a large "Dobson" style mounting, with
> > an eyepiece located at a convenient point on the side of the mirror
> > box... it would make more sense than the usual "Newtonian" layout
> > used with such mountings - which, for a large telescope, places the
> > observer on a tall ladder! (Would this configuration be called a
> > "Dobsmyth"?)
> >
> > -dave w
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >
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