[AZ-Observing] Re: An Eyepiece for the LXD75 10" ?


Brian Skiff wrote:

>>> ...long focal length eyepiece for my f/4 Meade LXD75 10". A
>>> number of years ago I bought a 55mm University Plossel...
>>> ...focal length is so long that the I have to look around the shadow of the
>>> secondary.
>>>      
>>>
>
>     Do the "eyepiece math"!  A 55mm fl eyepiece in an f/4 optic
>produces a 14mm exit pupil, and thus it is no surprise that you end up
>seeing the secondary shadow.  If you assume "low power" means something
>like a 5 to 7mm exit pupil, at f/4 this means an eyepiece between 20 and
>28mm focal length.  Notice that this barely takes in the 26mm eyepiece
>you rejected.  Do the arithmetic and consider again.  Remember also that
>at f/4 you'll need a fancy eyepiece to get sharp images, but on the
>other hand your eye is no good at large exit pupils, and one tends not
>to use such eyepieces for very long while viewing.  
>

Maybe (on this as well as the exit pupil being double the eye pupil of a 
good eye), but it is a new experience to me (since my observatory 
telescope, the only telescope I owned, is an f/15) to almost have Vega 
and the Double Double in the same field of view.
Stan.



--
See message header for info on list archives or unsubscribing, and please 
send personal replies to the author, not the list.

Other related posts: