[ATM] Long Focus Refractor

[Ken Hunter <atm_ken_hunter@yahoo.com>]

Richard wrote...

Actually, with a refractor, it is not as bad as that.
Using, as an example, a B270 iso-convex doublet, at
one degree off-axis, the net change in the
incoming-to-outgoing tangent is only 0.0000034.  The
image would shift about 0.004 inches.  Still, I think
that may
be difficult to follow.


*******************

This may be true for the difference in FOCUS POSITION
but an AXIAL ray diverted one degree will be displaced
1.745 feet laterally on a 100 foot radius.

The first Formula I used is for the circumference of a
circle,

pi x Diameter = 3.14..... x 200 = 628.318 feet

This is the length of 360 degree circumference so,

628.318 feet / 360 = 1.745 feet / degree at a 100 foot
radius. 

You'll get the same results by multiplying the Sine of
the angle (one) times the length of the side (100).

1 (Sin) = .01745  x 100 = 1.745 feet

The moon's image would be .872 feet wide (1/2 degree)
at the focal plane. That computes to 10.5 inches
diameter.

Ken Hunter





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