From: "Frank Q" 
To: 
Reply-To: "Frank Q" 


Hi All

>
> > >>"What are the optical advantages of short focal length.

It is not clear to me exactly what list members mean by "optical
advantage".  Some of the things listed below could be classified as
some type of (dis)advantage.

Constructional advantages - smaller, lighter - it is easily transportable, you
don't need a step ladder to get to the EP. Harder to collimate. You usually
need a bigger diagonal (bigger obstruction).

Figuring advantages - Fast mirrors are harder to figure. More work in
grinding it. (Negative advantages)

Viewing advantages - Some might be called Rich Field Telescopes. You get
"spectacular" views of star clusters etc.

Photographic advantages - shorter exposures

Optical characteristics - coma sets in more quickly compared to the same
mirror with a longer FL. I don't know off-hand how this relates to useable
angular field of view. In some instances, the focal plane is more strongly
curves (eg Schmidt camera). Might need more exotic eyepieces to cope with
the strongly convergent light cone.

Cheers
Frank Q

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