Re: [ATM] Baffles

[johncdeitz@comcast.net]

Nils: You ask the important question-how much baffling is necessary. I think that must be answered with experiment.
As to baffle around the mirror and at focuser I have bothered to do this as well. While I am convinced baffling it is necessary for maximum performance, I have NOT been able to see the effects of different degrees of baffling. This may be a result of the bright skies at my site and ilack of experience.
John Deitz
 -------------- Original message ----------------------
From: "Nils Olof Carlin" <nilsolof.carlin@telia.com>
> Anthony Stillman wrote:
> 
> > It seems the problem has been redefined to include
> > multiple scattering reflections.  OK, I'll bite.  Just
> > don't hold your breath, I chew slowly.
> 
> As I recall, the start of this thread was the question "How is it that 
> making the mirror end of the tube
> larger in diameter will reduce the number of baffles?". By now, I think we 
> have clarified the geometry enough to answer this, even if we have had a few 
> slightly different approaches.
> 
> But the broader question is what problem(s) do we want to solve by baffling? 
> Some aspects of secondary obstruction or of collimation *can* be solved, and 
> it is it is all too easy to jump to the conclusion that they also are 
> serious enough that one *should* solve them. Maybe, maybe not.
> 
> In the case of baffling, we have discussed how to baffle for single grazing 
> reflections in the lower end of the tube, but we haven't discussed under 
> what circumstances they are serious enough to matter.
> When observing Venus or Mercury before sundown? Likely, but for safety 
> reasons, an external baffling such as a house to the SW might be an 
> important adjunct. When observing faint galaxies five or ten degrees from 
> the full moon? Doubtful. Reducing the skyglow coming as a veiling glare over 
> the sky background itself? Possibly, but how much might a few percent 
> reflection matter? That lower part of the tube is only diffusely illuminated 
> through a small hole - most of the sky does not contribute.
> 
> Also, how much of the problem stray light comes via the secondary, and how 
> much outside it directly to the EP (or camera of course)? I find it likely 
> that the baffling of the focuser is much more important(including a fixed 
> baffle in the tube inside it - and this, opposed to the tube botttom, is a 
> refractor type baffling where you see the unlit side of the baffles). Do you 
> observe in the vicinity of streetlights that can directly illuminate the 
> parts of the upper tube directly visible from the EP? If so, would it be 
> better to use an external baffle such as a garden parasol?
> 
> "Baffling" the lower end of the mirror box, if open, can be important too - 
> some light may sneak by from the ground behind the primary - would a bent 
> baffle attached to the rocker box be an answer?
> 
> What about the minimalist telescopes with a pole carrying the focuser and 
> secondary, but no baffling "behind" them at all? would they benefit from 
> having a "flag" of black velvet suspended by other means? Separately 
> suspended baffles might make the telescope much less sensitive to wind.
> 
> Lots to think over....
> 
> Nils Olof
> 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/


_______________________________________________
ATM mailing list http://www.atmlist.net/