Re: [ATM] Baffles

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

Anthony,

I see from your images that you assume specular reflection by the ray that 
hits the edge of the primary, thus disqualifying a ray that passes by the 
edge of the tube opening to the opposite edge of the primary - it will hit 
the tube wall lower than the ray you have depicted, but by specular 
reflection it will miss the secondary. I have been more conservative here, 
expecting that the reflection in the latter case will be scattered widely 
enough that some significant light can reach the secondary and eyepiece.
My approach will be more demanding of baffling, but I don't know which 
assumption is the more realistic - it may depend on roughness of surface and 
paint used. A coat of velvet covering the relevant part of the tube may even 
be a better solution...

Nils Olof

------
> Using the parameters John supplied, and the values I
> was already using for everything else, I made some
> more drawings.
>
> The first drawing shows an 8 inch tube only.  A single
> baffle is needed.
> http://www.atmlist.net/contrib/atmer-at-flash-dot-net/6f8T8.jpg
>
> The second drawing has the tube inflated at the mirror
> end.  The powder purple and dark red lines show that
> no baffle is needed.
> http://www.atmlist.net/contrib/atmer-at-flash-dot-net/6f8T1025.jpg
>
> I drew a more accurate depictions of the 6 inch f/5
> with an 8 inch tube
> http://www.atmlist.net/contrib/atmer-at-flash-dot-net/6f5T8.jpg
>
> And did the same for the f/12
> http://www.atmlist.net/contrib/atmer-at-flash-dot-net/6f12T8.jpg
>
> The baffles Nils Olof identified in his last post are
> depicted in these images.  The smallest possible
> baffles are also depicted.  Their distance from the
> primary and extension into the tube are enumerated.
>
> Note that the extent of sky light that can reach the
> image by way of the tube and primary mirror is
> constrained.  These constraints are the upper end of
> the tube, the opposing edge of the primary, the edge
> of the secondary, and the edge of the field.  The
> secondary can play a dual roll in that it may limit
> the entrance rays as they head toward the opposing
> edge of the primary.  This is made apparent by the
> green line in the f/5 drawing.
>
> It's still baffles one, big tube zero.
>
> Anthony


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