[ATM] mirror support points as collimation points (was steel tubingfor mirror cell)

[Jay Kirkland <jaykirk2@compusmart.ab.ca>]

    Dick:
    Actually, if I remember correctly, there was also concern raised in 
at least one previous thread that the torque of turning the 
collimating/support bolts might also be transferred to the mirror 
itself, possibly also inducing flexure (?), hence several list members 
search for various bearings to be used at the point of contact with the 
support plates.
    I don't believe in edge supports either. I use silicone.
    The author of the mirror flexing article was Ernie Pfannenschmidt, 
Nov '03 S&T.
    Jay

 If the edge support

isn't well-nigh frictionless,

Who says you need edge support?   Some guy from the time of Adolf 
Hitler?   Eliminate the edge support and you eliminate the friction.   
While you are at it, you can also eliminate those evil mirror clips.

Long ago I build a mirror cell that works fine, does not require a 
foundary and machine shop, is easy to make, and has zero friction.   But 
I will not comment on this further; I am tired of pissing against the 
wind.   Let all the "experts" have their egos.

    In the S&T article, the writer judged the adjustment and accuracy of

his micro-flexing by watching how the image of Jupiter changed.

Unflexed, it looked okay, possibly the way it looks through most scopes

to most observers. He finished flexing when the image was really stunning.

If the author was Bill Kelly, I stayed at his place in Cottonwood, 
Arizona last week.   I owe him some mirror stress calculations.

    Anyway, I think it's a possibility. No direct evidence, just

anecdotal. It's simple to build a mirror cell using the three support

points as adjustment points, but it adds an unnecessary level of

complexity to the cell itself. I must say those three points have always

worked just fine for me with my small scopes. Big and thin mirrors more

prone to friction/stiction unknowns... I just don't* believe* in it.

Well, just stick to your belief.   After all, your belief, your 
religious faith, is a greater truth than any scientific or engineering 
knowledge.

I wish you luck in your future observing; you may be the first observer 
to discover an angel, djinn, or other spiritual being.


    And moving to an orthogonal system makes collimation both easier

(you only have to move the mirror in right angles - up/down and left to

right) and more precise (the wider stance between adjustment points). By

themselves, I think they makes changing over worthwhile.

If you want orthogonal adjustments on a larger or thinner mirror that 
requires more than three flotation points, plop yourself a six point 
flotation with 5 points at the 80% zone and one point in the center.   
Such a cell requires three levers, and the three centers of those levers 
are very nearly a right triangle.  You can assemble the whole thing with 
frictionless silicone pads as pivots, and with the glass bonded to the 
silicone, you don't need edge support or mirror clips. This 
configuration is only slightly less efficient than the usual six points 
at 78% zone flotation.

. . . Richard Schwartz


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