Re: ATM 3-Vane or 4-Vane Spiders

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

Richard,

> Sorry, even with no vanes at all there will be spikes caused by the edge of
> the aperture.  However, because the aperture edge is curved, the spikes are
> spread uniformly around each star image.  These edge spikes, as well as the
> spikes from spider vanes, might be suppressed if there could be a gradual
> blended shading around the obstructions.  Of course, there may be other
> undesireable consequences.

The particular spike caused by the edge of the aperture is, as opposed to spikes
caused by vanes, seen from the direction of the spike point. The view is called 
the "Airy disk". The remedy is simple though: do not use an aperture limiting 
edge on your mirror.
> 
> It's too bad that physics actually works.

Yeah, too bad. Then again, this distinguishes physics from politics, FWIW.

Nils Olof