Re: [ATM] PLOP_Obstruction parameter_What's wrong?

["Robert Houdart" <robert.houdart@cruxis.be>]

Rugo,

> There must be a problem with the way I am interpreting the contour
data. I
> would appreciate if someone could check this out and advise me, and
others > who might also be struggling to get the best out of PLOP.

With your data: Diameter: 508 mm (20"), Thickness: 41 mm (1.61"), Focal
Length: 2286 mm (90"), Secondary Size: 108 mm (4.25"), Material: Pyrex
7740,
PLOP gives the following results:

With obstruction:
Visible P-V Error: 5.72e-06 (lambda/96)
Visible RMS Error: 0.94e-06 (lambda/585)

Without the obstruction:
Visible P-V Error: 8.88e-06 (lambda/62)
Visible RMS Error: 1.12e-06 (lambda/490)

I read these values directly from the "Run Plop" window.
Is it possible that you read the values from somewhere else (the Color
Plot?), and that you're not excluding the zone that lies in the shadow
of the secondary?

Robert



-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
Of rugo@iinet.net.au
Sent: maandag 5 maart 2007 5:36
To: atm@atmlist.net
Subject: [ATM] PLOP_Obstruction parameter_What's wrong?

Hello all
Can someone enlighten me about a possible 'anomaly' I have found using
PLOP.
I appear to find when I run PLOP with, and without, including a figure
for an
obstruction (secondary diameter) I get different results. I get a better
result when calculating a cell that does not include the secondary
diameter.

For example, the mirror is pyrex 20 inch, 1.61 thick and f/L 90 inch. I
want to
design an 18 point cell.

Factoring in a 4.25 inch secondary there is a 1/47 wave PV across the
mirror,
with a 4 inch secondary it is 1/49 wave PV while with no obstruction
factored
into PLOP the result is 1/52 wave PV.

Some may think that the difference is too small to be an issue, however,
I do
not believe David Lewis would have gone to the trouble to include in
PLOP the
obstruction parameter if it added nothing of value.

Cheers
Rugo

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