Monday, May 27, 2013

Since The Weather Is Bad Anyway...

I mean, it snowed here on Wednesday!  And the weekend has been nothing but clouds and rain.  Once I successfully adjusted the spider legs to get the diagonal mirror centered in the telescope tube, I was able to collimate the telescope quite quickly.  But when I changed the angle of the telescope so that it was no longer horizontal, the collimation was off again.  I am pretty sure that the reason is that there are two parts of the diagonal holder that are too flexible:

1. The legs are made of .0325" aluminum -- and that is probably too flexible.  I can replace them with 20 gauge steel, which would be the same thickness (and optical path interference) but three times as stiff.  I may also go from 2" front to back to 3" front to back, which would improve stiffness even more.  The steel will weigh more, but only an ounce or two.

2. The central body of the diagonal holder is made of acetal, which is easy to machine, but has about 1/20th the Young's modulus (flexural deflection) of aluminum.  I think I will pick up 3" of .25" ID aluminum tubing, perhaps 1/8" wall, and use that as the new central body.  That should improve stiffness substantially with no  real difference in weight.  (The existing acetal part is fairly thick, so probably about the same net weight.)


  1. Snow? What happened to all that Global Warming we were all supposed to be worried about?

    (Yeah yeah, I know that the new term is "Climate Change." But why let that get in the way of a good joke?)

  2. You could also stiffen the spider legs by putting a crease in them. (kinda like how they make sheet metal stiffer for lunch carts by creasing a diamond pattern in it.)