Re: [ATM] What is that Image size in Calculations

[Alexis Cousein <al@sgi.com>]

Geogre Nikolidakis wrote:
> Considering that one of my low power eyepiece is the 35 mm panoptic with a
> field stop about 39 mm ~ 1.56", then illuminate the 0.5" that is about 33 %
> of full field stop of the panoptic. 
> Then what is the benefit using the 2" eyepiece than one of 1 1/4" ?
> 
Illumination doesn't suddenly drop to zero beyond the fully illuminated
zone. Newts are frequently designed to illuminate the edge of field of
something like a Pan 35 only 70% if they are to be used visually, and
SCT owners frequently use eyepieces where the edge is only illuminated
40%.

40% of the light still shows you more than a black field stop ;). 70%
illumination corresponds to the light collected by a scope with an
aperture that is 84% a large as the original aperture...

My f/4.5 scope also has a fully illuminated field "only" that large,
but at the edge of my 26T5 illumination is still 86%. My 16T5 has its
field stop illuminated 95%.

It all depends on the f/ratio - slower and smaller scopes have
illumination that drops faster beyond the fully illuminated
field.

Only Newts designed to use for astrophotography with large
sensors tend to be designed to fully illuminate a very wide field.

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