Re: [ATM] Collimating, the eccentric way

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Rob wrote:


> Wait a minute,

Seems we've waited about 4 months - no worry ;-)

> I want to agree, that the precise alignment of the secondary
> 90 degrees to the optical path is not necessary, but imagine the cone of
> light that is reflected, less or more than 90 degrees, even a small
fraction
> would distort cone, would it not? And aren't we talking about the nano
level
> here?

Distort? If not 90 deg, the secondary (designed for 90 deg, with a sqrt(2)
ratio of axes) will look ever so slightly elliptic from the focal plane, and
the fully illuminated FOV (the cone cut at the f.p.) will also be slightly
elliptic. This would not really be noticeable - not with the kind of
deviations to expect of a normal geometry (the offset is typically around
1%, perhaps 1.5% for a very fast scope) meaning e.g. that if you have the
sec. centered but offset collimation, the deviation from 90 deg if the
focuser is perpendicular to the tube will be about 1 deg, and the secondary
will appear about 2% wider than its height seen from the focuser. Can't
believe this is a serious problem. If the focuser looks tilted, it may be,
but even so, it must be pretty skewed to be a problem (if you still can
center the secondary). I would say a non-offset collimation would mean a
much more serious effect on the fully illuminated part of the FOV.

Or do you refer to something entirely different?

Nils Olof


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