Re: [ATM] Baffles

[johncdeitz@comcast.net]

Hello Nils:
> 
> So am I, I recall an Astronomy mag aricle mentioned in this thread . I only 
> have a vague recollection of having read an article advocating (what I claim 
> to be an incorrect) refractor-type baffling for reflectors. I have no 
> recollection of the author or if I still have the issue available - what 
> issue was your article???

 My article was in Sept. 1996 and was advocating Newtonian type baffles as seen in Telescope Optics (not refractor).



> Being inspired by this, I just did an experiment!
> 
> I took 2 pieces of slightly rough wood, painted with a not entirely flat 
> black. One larger piece I held to see it from a grazing angle (acting tube 
> wall), and a narrow strip held at right angles to this (acting baffle). I 
> held a strong lamp beside my head, shining at a similar grazing angle away 
> from me. Here, it was very obvious that the "tube wall", reflecting light 
> away from me, was significantly darker than the "baffle" itself. Repeating, 
> this time in front of a mirror reflecting the light from the lamp at a 
> grazing angle *toward* me, it was even more obvious that this grazing 
> reflection was far brighter than the baffle (though still illuminated from 
> its visible side). This was the case for a not too narrow angle of view.
> 
> Thus, with a minimum of material and in a few minutes I could demonstrate 
> that for *this* admittedly not the best material,
> 1) John's baffling scheme is, as I suspected, counter-productive,
> 2) Anthony's assumption of specular grazing reflection is too "liberal" and 
> that my more conservative assumption that a grazing reflection will add 
> light even if a specular reflection would miss the secondary, is indeed 
> justified.
> 

 
This is convincing evidence- thanks.

> 
> For a telescope, I would suggest taking a photo through the empty focuser 
> opening (or simply checking visually) during daytime to see if any 
> significant stray light is visible, and if so, identify the path.

Identify the path? Difficult! CCD flats with and without baffles would likely be better.

For an image of my "tube within a tube" see
bmaa.freeyellow.com/Constellation/NOV2000.html

John Deitz


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