🚀 go-pugleaf

In article <1993Jan12.224443.1547@linus.mitre.org> chaloux@mandolin.mitre.org (Dave Chaloux) writes:

>An images of a star in focus consists of an Airy Disk and diffraction rings
>around that disk. An unobstructed telescope like a refractor can, if it is
>perfectly made put about 84% of the light into the central disk. Any obstruction
>(or under or over correction of the optics) puts more of the light into the
>diffraction rings.

...

>The answer isn't this simple however. Obstructed reflectors of larger diameter
>can be gotten for much less money than equivalent refractors. If the reflector
>is well made, the larger diameter of the mirror can more than make up for the
>loss of the light due to the obstruction. Doug McDonald has said on numerous
>occasions on the Net that given perfect optics, a Reflector of size a and
>with an obstruction of size b will perform as well as a refractor of size
>a - b/2. 

This reminds me of a (possibly naive) question I have on this topic:

Some people use this argument (obstructions causing more light in the
diffraction pattern to be in the outer rings) to argue that small refractors
have an intrinsic advantage over significantly larger reflectors.
Is it possible for a larger, obstructed scope to be largely immune to
this effect (more light in the rings) on the diffraction pattern, when
compared to a smaller, unobstructed telescope, like a refractor?
True, obstructed scopes dump more light into the rings, but the diffraction
pattern of a large scope is so much smaller that this would seem to have no 
real effect -- especially if the larger scope is sufficiently larger that
the diameter of its first diffraction ring is less than that of the Airy
disk alone of the smaller scope.  Is this reasonable?


I'm not an optics jock, so i'll yield to those who are.
-- 
David Nash                  | Gradual Student, Chemistry
                            | University of Illinois (Urbana)
(dnash@uxa.cso.uiuc.edu)    | This .sig is made of 100% recycled electrons.
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