Re: [ATM] lensmaker for a very long focus objective

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Michael Lindner wrote:

> However, a flagpole bends in the wind. Without something to keep the two 
> components (objective and eyepiece) a fixed distance from and square to each 
> other, viewing would be impossible. A 1 degree tilt of the objective would 
> result in the focal plane moving about 1.5' to the side!
> 

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.

-- 

Rick S.

http://users.rcn.com/rflrs

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