From: Mark VandeWettering 
To: Marco Miglionico 
CC: Goran Hosinsky , atm{at}shore.net
Reply-To: Mark VandeWettering 




Marco Miglionico wrote:

> 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).


For most of us, the ecliptic falls well short of zenith, so this is even
less of an issue than it would be for a telescope that you used for more
generic viewing.


> 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.


Some of the best planetary views I've ever had have been through a 10"
f/10 that was certainly nothing to look at, but provided great views
through.

        Mark


>
> 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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