R: ATM Focal length

[" Gianluca Carinci" <g.carinci@iol.it>]

-----Messaggio originale-----
Da: Wouter van der Schagt <frenzyr@writeme.com>
A: atm@shore.net <atm@shore.net>
Data: venerd́ 9 luglio 1999 23.26
Oggetto: ATM Focal length


>
>Can somebody please explain to me the idea of a longer focal length, and
the
>relevance with the diameter ?
>
>Thanks,
>
>Frenzyr,.



Hi, Frenzyr
surely, focal lenght and entrance pupil are between the most important
parameters wich at first describe a telescope, but  to say more you should
at least say the type of telescope and application in wich you are
interested !
At now, in fact, few is to say apart from the fact that their ratio defines
the "speed" of the system, id est the capability of the telescope to bring a
more or less bright image of an object at a certain scale on the focal
surface.
Depending from several others parameters, F.L. and D have also influence on:
- focal surface ROC
- full illuminated field extension
- aberrations blurs on and off axis
- performance with a certain eyepiece type
- instrument overall dimensions and weight
- optics (and related mechanics) price
- good or poor performance for a certain application...
- ...more and more...
let us know and, in the meanwhile,
Clear Sky to you all