Re: Diffraction rings

From: Jerry (jerry_at_a5.net)
Date: 11/29/04 

Date: Mon, 29 Nov 2004 01:52:33 -0600

The distance you must travel inside or outside of focus to achieve
DR's varies with focal length; differs for the 80mm widefield refractor
vs the longer focal length lx90. Rack the lx90 further in or out to
find the diff rings vs. your 80mm refractor.

Steve Maddison wrote:

> Hi all,
>
> I've been reading up on optical theory, but can't seem to find any
> answers to a query or two I have about diffraction rings.
>
> I've had a Meade LX90 for several months, but to this day never seen any
> hint of diffraction rings around the Airy disk of any stars, regardless
> of brightness. I never thought anything of it, but I recently got my
> hands on an Orion 80mm ED refractor, and in this scope the rings are
> obvious, epecially at powers above 100x.
>
> I'm trying to get the reason for this straight. From what I've read, I'd
> expect the rings to be more obvious in the LX90, due to the central
> obstruction, whilst the opposite is true. I'm curious as to which
> factors affect the diffraction pattern of a scope. I can imagine things
> like the quality of the optics and collimation have something to do with
> it, but can't seem to work out how this all fits together.
>
> Whether or not such rings are visibile doesn't bother me too much - I
> find a nice, sharp, ringless disk pleasing enough, although a disk with
> rings also has a certain beauty to it. Is there an ideal or prefered
> situation?
>
> Any, even partial, explanation would be most appreciated, as would a
> link to a web site which covers such topics in detail.
>
> Thanks in advance, and clear skies to you,
>
> Steve
>
> --
> Steve Maddison
> Den Haag, The Netherlands
> http://www.cosam.org/

Relevant Pages

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