[Leica] 21.4 meters across and only f/8 !

[henningw at archiphoto.com (Henning Wulff)]

>>  >http://www.gmto.org/tech_overview
>>>best,simon jessurun
>>
>>Isn't that about 25m across (3 x 8.4m) and a focal length of 18m 
>>which results in approx. f/0.7?
>>
>>f/1 and larger (smaller number) are usual apertures in large mirror 
>>telescopes.
>>
>>--
>>    *            Henning J. Wulff
>>   /|\      Wulff Photography & Design
>>  /###\   mailto:henningw@archiphoto.com
>>  |[ ]|     http://www.archiphoto.com
>>
>"The final focal ratio at the straight Gregorian focus will be f/8.4 
>with an image scale of one arcsecond per millimeter"

I don't see that on the page for which you posted the link, but in 
any case that quote refers to auxiliary optical units which will 
increase the focal length. The mirrors themselves are much faster, as 
the data on the link noted.

-- 
    *            Henning J. Wulff
   /|\      Wulff Photography & Design
  /###\   mailto:henningw@archiphoto.com
  |[ ]|     http://www.archiphoto.com