Re: [ATM] Plop Flop

[mdholm@telerama.com]

I reran the cells with 1.625 inch thickness and Pyrex as the glass type.

The K & B 18 point cell comes out a little marginal now.

RMS 4.03 nM  (1/124 wave)
P-V 14.5 nM  (1/34.5 wave)

This is still usable.  You won't be able to detect optical deficiency due to the
se deformations.  One point, this cell gives a deformation plot looking a little
like the plot of parabolic correction: low in the center, high in the 70% zone
and low again at the edge.  If your mirror is a hint over corrected, or has a
trace of turned edge, this might not be a good cell, because the cell induced
deformation would add to the existing errors.  On the other hand, if the figure
is quite good, you won't notice the effect of the cell.  If the mirror is a bit
undercorrected, or has a high edge, this cell might help a little.

The Plop optimized 18 point cell still looks pretty good at 1.625 inch thickness.

The RMS deformation is 1.04 nM (1/480 wave).  The P-V deformation is 7.8 
nM (1/64 wave).  The focus shift is -0.107 mm.

The dimensions of this cell are (stated in the same terms used in K & B):

Radius of outer support points      7.818"
Radius of inner support points      3.899"
Base of triangle (isosceles)        4.047"
Altitude of triangle                3.652"
Balance point from vertex           2.435"
Length of bar connecting triangles  6.334"
Radius to center point of bar       5.485"


The 12 point design still looks pretty good too.  It now looks better than the K
& B 18 point.

I have used Jeff Anderson-Lee's 12h layout as shown in the 12-point 
section at http://pong.telerama.com/~mdholm/atm/cells/index.html

Optimized for your mirror, this gives:

RMS deformation  2.11 nM  (1/237 wave)
P-V deformation  14.4 nM  (1/34.8 wave)
Focus Shift -0.107 mm

These are also quite acceptable numbers, indicating very good support.  

The dimensions are:

Radii of the 3 inner triangle mirror support points    83.97 mm
Radii of the 6 outer triangle mirror support points   189.24 mm
Radii of the 3 bar mirror support points             183.10 mm

Triangle base (Isosceles)    142.10 mm
Triangle altitude             91.43 mm
Triangle pivot altitude       30.48 mm
Triangle balance point from vertex   60.95 mm
Radius of triangle pivot      144.92 mm (this is the distance from the 
cell center to the attachment point between the bar and the triangle)

Bar Length                   167.31 mm
Bar Pivot point              125.48 mm
Bar Pivot Radius             137.42 mm  (this is distance from the cell 
center to the attachment point from the cell back structure to the bar)

Mark Holm
mdholm@telerama.com
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