From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


I made a 10" f/8 and it is not used today because it was not a very
portable instrument.  I also used a 10" f/10 with a 1" diagonal. 
I liked the f/8 better.  Planetary use is my main interest, and I find that
15% obstruction is on a par with 10%, i.e. indistinguishable.  The warnings
about the immeasurable edge condition of the secondary are valid, I think,
tho can't prove it.

Keep it simple and get a good ~1.5" diagonal for the 10" and
you'll be real happy. Your tolerances will relax and so will you.

I use a moveable step ladder with hand rails for most observing.  It helps
to steady oneself or sit on the top step, even for a 6" f/10.5, and
8" f/7 which are my usual instruments.  Don't worry about reaching the
eyepiece at zenith, just make a stepladder for your comfort.

Colin

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of Marco
Miglionico
Sent: Friday, May 16, 2003 2:47 PM
To: Goran Hosinsky; atm{at}shore.net
Subject: Re: ATM Planetary scope idea



Can a planetary scope not be satisfied with an F8 10in (250mm) mirror with
1in (25mm) secondary and low profile focuser? It would not  be
uncomfortable to use unless your planets are at the zenith all of the time!
(Or if you are very short).

Plugging in a few figures into 'Sec' gives a good indication of what might
be needed for a planetary scope. At the above specs you still get a Fully
illum. FOV to some arcmins'.

Texereau seems to think that 10% obstruction by diameter is good enough to
'cause no appreciable change in the image'. (only 2% drop in energy from
central diffraction disk compared with zero obstruction.)

With many optical elements introduced, the wavefront  and/or ease of collimation
may suffer, defeating the purpose of such a scope.

I would say this as I am scared of complex scopes.

Marco Miglionico.



----- Original Message -----
From: Goran Hosinsky 
To: 
Sent: Friday, May 16, 2003 3:33 PM
Subject: ATM Planetary scope idea


>
> Hello,
> I would like comments on the following idea for a planetary
> scope. The goals are: long focal length well baffled Newton,
> minimum secondary obstruction and comfortable viewing position.
> I think the goals can be reached with this solution but I
> might be missing something fundamental.
>
> -250 mm f/12 primary mirror, placed about 300 mm above ground.
> -Secondary 100 mm before focus at 3200 mm above ground
> -Tertiary mirror 230 mm from optical axis throwing the light
>    down parallel with the optical axis
> -50 mm acromat fl=380  600 mm from primary mirror focus This
>    will give an image 1050 mm further down from the lens with
>    3x amplification giving a f/36 system
> -flat mirror shortly before focus angling the light normal out
>    from the tube for the eyepiece mounting at about 1550 mm above
>    ground
>
> The above introduces 2 extra plane mirrors and one objective. The
> plane mirrors are near focus and should not be too bad for the
> image.
>
> Variations of this might be
>
> - use a singlet lens and color filter when observing
> - use two identical photographic objectives front - to - front.
>   The first with focus in primary focus giving parallel light
>   out, the second focusing this parallel light at a convenient
>   distance.
>

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