Re: [ATM] More on my Mak-Cass project

[David Whysong <dwhysong@gmail.com>]

Hi Mike,

Thanks for the reply. I will study your article on Cassegrain baffling.

The idea behind adding the knife-edge baffles is to approximate the
conical shape by using a cylinder with "fins". I'm considering this as
a possible improvement over a simple conical baffle, because the
knife-edge "fins" should stop any grazing reflections from slightly
off-axis light. My concern is that this might cause ghosting from
on-axis light. The knife-edge baffles would have to be very, very
black.

Putting knife-edge baffles outside a cylindrical primary baffle would
stop light from reflecting off the outside surface of the baffle tube
at grazing angle.

Does that make sense?

- David

On Fri, 25 Jun 2004 19:55:31 -0500, Michael Peck <mpeck1@ix.netcom.com> wrote:
> 
> At 14:56 25-06-04, David Whysong wrote:
> >My question concerns the baffle tubes. In the schematic, they are solid
> >pieces with triangular cross-sections. I was thinking of making them
> >simple, straight tubes and adding knife-edge baffles (to the outside of
> >the primary / inside of the secondary baffle) to stop glancing reflections
> >from slightly off-axis light sources. But I am worried that this could
> 
> David:
> 
> In general the optimal baffle for the secondary will be conical in shape,
> assuming you want some non-zero size field to be both fully shielded and
> unvignetted. Depending on your application you could make it cylindrical
> and accept some vignetting, or make the secondary larger than it would
> otherwise need to be.
> 
> The primary baffle most likely could be made cylindrical without problems,
> but you really should raytrace the design to verify that. But why would you
> want to add knife-edge baffles to the *outside* of the primary baffle?
> 
> There's some published literature on baffle design, but what I've seen
> applies to designs with the stop at the primary. The math may be a little
> different when the stop is at the front of the OTA. If you follow my links
> I've simplified baffle design to high school algebra.
> 
> Mike Peck
> 
> _________________
> 
> Michael Peck
> email mpeck1@ix.netcom.com
> Wildlife photography page http://home.netcom.com/~mpeck1/index.html
> Amateur telescope making http://home.netcom.com/~mpeck1/astro/astro.html
> 
> 
> 
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-- 
David Whysong
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