[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

Re: [ATM] My scope

Mark Holm wrote:
> Gerald Clay wrote:
> 
>> BTW it's an 8" mirror.  What focal length would be good for viewing the planets and deep sky images?
> 
> Focal length isn't so critical a variable as you might think in 
> observing performance.  

but central obstruction is.  good planetary scopes have a tiny or no central 
obstruction (5-10% vrs 30%+ for a DSS).  tiny central obstructions that match 
the light path means high f-number.  There is nice cass design (referenced in an 
earlier message) that has a high f-number but a short tube.

> If the planets aren't big enough, and the mirror is good enough to make 
> the higher magnification usable, treat yourself to a shorter focal 
> length eyepiece in addition to the 25 - 27mm or so that you should 
> probably start out with.

with most dss (deep sky scopes) you go from small fuzzy to big fuzzy where as a 
pls (planetary scopes) go from small sharp to big fuzzy.  :-)



-- 
Speech-recognition in use.  It makes mistakes, I correct some.
_______________________________________________
ATM mailing list http://www.atmlist.net/