Re: SV: ATM eyepiece focal length

["B. Pepin" <atmjedit@conceptsnet.com>]

Easier than guessing, use a millimeter scale to measure the diameter of the
bright circle of the exit pupil at the eyepoint, using a simple magnifier or
objective of known focal length and clear aperture. Exit pupil = objective
aperture/magnification.

.
----- Original Message -----
From: James W. Burrows <burrjaw@halcyon.com>
To: <atm@shore.net>
Sent: Monday, October 09, 2000 7:36 PM
Subject: Re: SV: ATM eyepiece focal length


>
> At 23:44 2000-10-09 +0200, Nils Olof Carlin wrote:
>
> >Do you have the binoc objectives? If so, try focus some long distance
> >object (moon, skyline) and measure the distance from the middle of the
> >objective to the image - then divide by 10.
>
> Another possibility is take any old magnifying glass, measure its focal
> length as Nils suggests, then use it as an objective with your eyepiece,
> look at something far away and guess at the power P (number of actual
> telephone poles = image telephone pole).  Then eyepiece focal length =
> objective focal length/P.  Even handier, if you have one, is a removable
> camera lens.
>
>
> -- Jim Burrows phone 206.244.2933, fax .0294
> -- mailto:burrjaw@halcyon.com
> -- http://www.halcyon.com/burrjaw/
> -- Seattle N47.47233, W122.36620 (WGS84)
>
>