Re: [ATM] Newbie Eyepiece Question

["vladimir sacek" <vlad@copper.net>]

Bryan,

You can quickly figure out approximate size of fully illuminated field
and ~50% illumination field diameter (still acceptable edge illumination
for visual observing) from the diagonal size and width of the converging
cone at the diagonal. The cone width is obtained by dividing
diagonal-to-focus distance by F#. In your case, diagonal minor axis is 1.5"
and width of the cone for, say, 8" diagonal-to-focus separation is slightly 
over 1".
Field of full illumination (diameter) in this case would be
1.5-1~0.5", and approx. diameter at which illumination drops
to 50% would be 1.5+1~2.5".

While the actual diagonal-to-focus separation for your scope is likely
somewhat different, size of sufficiently illuminated field is still
larger than the minimum necessary for even widest 2" eyepieces. At 0.8" 
off-axis
(all one really needs to care about) field illumination is likely to be 
~70%.

Vlad




> My main scope is a homebuilt 8" f7.73 reflector. It's my first scope
> and serves me quite well. I am considering buying a 2" Panoptic
> eyepiece. ... Admittedly I am a bit
> foggy about the light cone from the 1.52" secondary as it relates to
> the view in the eypiece.
>
> Any advice would be much appreciated.> 


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