From: "James Lerch" 
To: "Michael Peck" 
Cc: "ATM List" 
Reply-To: "James Lerch" 


Mike and All,

Mike as always, excellent work, thank you!

As some perspective, we do have another data point form a different, but similar
optic (12.5" F/4.5")

Below values are Surface RMS in nm.

Optic A

Robo                              =  21nm
Couder Mask / Foucault =    3nm
------------------------------------
Difference                            18nm

Optic B
Interferometer    =    38nm (coma, astig removed)
Robo                   =    20nm
-------------------------------------
Difference                   18nm

So, same size, F/# optic, the difference between Robo and two different tests is
18nm RMS surface.  I must say that's something substantial, which shows a
systematic error with Robo...

Now, from the current intereferometry, CAN we calculate a best fit conic
constant (b), and the surface RMS?   If so, we can calculate how much Robo
has
to be off in either Zone radius or Longitudinal readings for this to be true.

As I see it (assuming Robo to be in error) we have three possibilities

#1  Robo can't measure Zone Radius or Longitudinal values with any accuracy

#2  Something about the Camera lens is changing the readings

#3 Digital knife edge testing is flawed.

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

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