Re: ATM 16" F/33 valid design?

[Joe Mayenschein <mayen1@mwt.net>]

Hi Frank,,

Thanks for the reply,,

I agree f-70 would be crazy,, that's where I was hoping  some of the ray trace
guru's could play with it some.  See with that say 10" f-6 primary,  how "Fast"
you could make it with simple "Edmund" Specials lenses used as the convex
secondaries (spherical of course)  how fast (low of a f- ratio) can it go before
undesirable image degradation occurs.

In other words,, a primary with a standard parabolic f-6 primary. and a
spherical secondary using a off the shelf lens as is. for the cass secondary.
how slow can you go before it falls apart.?

a no figure the secondary scope.

Joe

Frank Ward wrote:

> Joe,
>
> Nick Loveday designed a system in the early 80's that
> accomplished what you want to do with a second convex
> parabolic mirror replacing the diagonal. S&T June 1981
> page 545 Gleanings for ATM's A "Folded Newtonian" with
> Dual Focal Lengths
>
> The center of the primary hidden by the diagonal shadow
> was used a second time for the reflection from the secondary.
> The rays  then returned thru the secondary to a diagonal and on to
> the focuser.(600X with a 12.5" and a 10mm WA eyepiece)
>
> In a conversation with him last year he admitted that no one had
> constructed a working model of his design. (I have made the optics
> and they are aluminized, but I too have not constructed the upper
> cage necessary to install them with the precision necessary to get
> the possible f/18 the design allows.) He attributes the lack of interest
> to the comment Andy made in a post earlier today or yesterday.
>
> In today's world the quality eyepieces and barlows available and the price
> charged so "low" compared to a full scope fabrication that the same
> wonderful results can be obtained without resort to multiple surface
> reflections.In your very innovative design I count five reflections, for me
> an "unacceptable" light loss on objects viewed at f/70, where there
> will be next to no light as it is. In your design a 32mm eyepiece would
> be your lowest useable eyepiece considering a 50X useful limit on mag.
>
> I am not trying to disuade you. Far from it. Your thinking "outside the box"
> by including two focusing mechanisms is quite elegant and cries out to be
> used in >some< fashion.  I hope you get back many replies from designers
> far better than I with far better and more constructive comments.
>
> Oh, and thank you for taking the trouble to present your ideas and drawings
> in such a clear fashion. If you lived in Atlanta I'd like to be a neighbor
> of yours.
> A few Friday nights with feet up on a sofa bouncing around ideas like that
> would do me a world of good.
>
> Best wishes,
>
> Frank Ward
> Atlanta, GA
>
> ----- Original Message -----
> From: "Joe Mayenschein" <mayen1@mwt.net>
> To: "Andy Saulietis" <iss@pvtnetworks.net>
> Cc: <atm@shore.net>
> Sent: Tuesday, January 15, 2002 7:03 PM
> Subject: Re: ATM 16" F/33 valid design?
>
> >
> >
> >
> > Andy Saulietis wrote:
> >
> > > At 08:12 PM 1/15/02 +0100, you wrote:
> > > >
> > > >
> > > >Attention focal length extremists...
> > > >
> > > >This matter of sanity in focal length choice comes up
> > > >periodically. I recall The Simak paper in Astronomy
> > > >magazine in April 1984 mentioning that focal length
> > > >of 120"
> >
> > {snip}
> > Please check out the below page of a project of a EXTREME long F-Ratio
> > scope I was thinking of trying.  what's everyone think?
> >
> > http://www.qsl.net/wb9sbd/path.html
> >
> > Joe
> >
> >