Re: ATM paramythioti telescope

[Nik Cain <nikcain@yahoo.co.uk>]

Hi Bob,

Here's the stats according to the magazine;

Ouverture: 160mm (optimale pour la turbulence moyenne des sites européens, dont
le paramètre de Fried ne depasse pas 13cm). (I don't know who Fried is, but
from the F/D the primary mirror must be 130mm diameter, and the 'Ouverture' is
referring to the aperture of the scope's tube rather than the mirror diameter)
Focale: 960mm; F/D = 6.  
Champ apparent: 1º
Miroir primaire: sphérique
Miroir secondaire: sphérique
Obstruction centrale: 23% (en proportion de diamètre du miroir primaire)
Pouvoir séparateur: 0.72"  (I'm not sure what this means in english, focusser
travel p'haps - and I don't know why they's changed units either).
Grossissement minimal: 30x
Grossissement maximal: 360x
Tube en fibre de carbone: longueur 54cm en prototype, et 42 ou 34 cm en version
définitive. Tube-allonge au coulant 50.8mm avec un porte-oculaire au coulant
31.75mm. (tube is 54cm long, and the final version will have a collapsable tube
34cm long?).

I haven't tranlated all of it because a) it looks pretty obvious, and b) my
french is appalling ;-)

>From the rough diagram they give, the separation of the primary and secondary
is a bit more than 3/4 the focal length of the primary, so that the focal point
lies slightly closer to the primary than the secondary (but that's not to say
that their diagram is exact at all?). The relay lenses they've drawn are pretty
abstract, but basically they've put a square near the entrance which seems to
collimate the light, then a concave-convex lens (backwards C shape), then
another square close to that, followed by the eyepiece like (warning! bad ASCII
art time!);

                       \
                       |
 \                     |
 |           .   �    ) �  >   
 /                     |
                       |
                       /

. is focal point, the > is my attempt at an eye, and I hope the squares come
out.

nik


--- Bob May <bobmay@nethere.com> wrote: > 
> The initial look shows a lot of spherical abberation and I am not finding a
> solution where the spherical is minimized and that means that he's also got
> to get rid of the spherical abberation in the lenses and that's going to be
> a problem because he is now going to have to deal with color problems (relay
> lenses by thier nature, tend to minimize the color errors but do nothing for
> the spherical abberation) that are going to pop up.  Sounds to me at this
> point that somebody hasn't done thier work properly.  I might note that any
> convex secondary increase the spherical error rather than lessening it.
> A scope design it may be to some but it's just an arrangement of mirrors and
> lenses that reflect the light about and it unfortunately as I have looked at
> (considering your short description of the arrangement) the design is not
> worthy of anything as it's design doesn't come to even a marginally decent
> focus.  Changing the curvature of the mirrors to a paraboloid would change
> it to the already well known Mersenne scope design as Mr. Bone has so nicely
> done.
> If you have some better info as to the details as to what the spacings,
> radii, etc. of the design, I'll look at it again.  Optics Workbench makes
> slapping designs together very easy.  It took me about 5 minutes to explore
> the design.
> Bob May
> My new web space address is http://webu.wigloo.com/bobmay/ or
> http://nav.to/bobmay
> and my new email address is bobmay@nethere.com
> Bob May
> 
> 


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