From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


Hi Kevin
 I've not done and math on your design but there
is one thing you need to check. You need to look at exit pupil for each of
the surfaces. I had what I though was a real nice design, when I just
figured focal lengths. Once I analyzed exit pupils, I found that my eye
needed to be someplace inside of the telescope. Exit pupil changes when you
place other optical elements in the light path. You don't want to make
Gallileo's mistake.
Dwight

>From: kwhitefire{at}juno.com
>
>Of course, I'm always the theorist.  This is what I have:
>
>This design features 4 mirrors on-axis.  The field curvature is in excess of
250 miles with excellent construction and polishing techniques.  There are
no exotic curves, though the primary does have a huge perforation.  Field
of view is .25 degrees half-angle.
>
>All preliminary tracing done using Dave Stevick's Spotplot, Kevspot version,
which allows the operator to choose paraboloids as +1 or -1.  I used -1 in these
numbers to determine the figures.
>
>The data:
>Primary Mirror:
>D = 13.2 inches
>roc = 82.5 inches
>b = -.8305
>
>Secondary Mirror:
>D = 3.25 inches
>roc = -17 inches
>b = -.0148
>
>Tertiary mirror:
>D = 7.75 inches
>roc = 50 inches
>b = -.0949
>
>Quaternary mirror is a flat placed for convenient viewing between primary and
tertiary mirrors.
>
>Primary to secondary distance = 32 inches
>Secondary to tertiary distance = 64 inches
>Tertiary to quaternary distance = 26 inches
>Quaternary to focal point = 3.35 inches
>
>The results:
>f/D system = 6.17
>Astig = -.003382
>Coma 'S = -.000579
>Coma 'T = -.001738
>Field curvature = 1361912 inches
>Approximate tube length: 77 inches
>
>Newtonian comparison, same D and f/D:
>Astig = .0015
>Coma 'S = -.000583
>Coma 'T = -.001754
>Field curvature = 81.0424 inches
>Approximate tube length: 95 inches
>
>It looks a bit like this:
>---------------- )                  )
>        )------- )    /             )
>---------------- )                  )
>                      ep
>        2        1    4             3
>
>Kevin of Eastern Iowa
>Seeker of the Darkness
>

--- BBBS/NT v4.00 MP