RE: [ATM] RE: ATM Schiefspieglers in Oslo LT

["Donald Good" <donald.good@comcast.net>]

OSLO Help file says this about the Distortion Plot: 
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
vvvv
This function plot a distortion analysis of the current system in its
current configuration, with 3 graphs: 

The distorted image of a perfect grid. The user is given a choice between
many different outputs (plot reference grid, plot symbols only, link
distorted grid to reference points, etc.). The grid size can be defined in 3
ways: 
	Automatic: the grid is given a square shape, whose diagonal matches
the ray height at Full Field (i.e. Field Angle or Object height) 
	Field Point Set: If field points are defined in the field point set
with BOTH non zero FBYs AND non zero FBXs, those values are used to set up
the image shape of the rectangle. 
	User-Defined: enter the values of the X and Y dimension for
analysis. For example, 24x36mm. 

The distortion curve in PERCENT, taken along the diagonal of the defined
rectangle. 

The distortion curve in MICRONS, taken along the diagonal of the defined
rectangle. 


NOTE: The results are incorrect for a curved image surface.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^
The above NOTE might mean that the Distortion Plot is meaningless if you
have a curved image surface.  I know that the image plane is not
perpendicular to the optical path at the focus.  It has about a 7 deg tilt.

Also, from the OSLO web site at http://www.sinopt.com/
Online documentation has this to say about distortion:
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
vvvvv
In addition to ray-intercept curves, optical design programs usually display
field sag plots showing the locations of the tangential and sagittal foci as
a function of field angle, and distortion curves. In the case of distortion,
there is the question of what to choose as a reference height. It is
generally easiest to refer distortion to the paraxial chief ray height in
the final image surface, but in many cases it is more meaningful to refer it
to the centroid height of a bundle of exact rays from the same object point.
Again, it is important for the user to know what the program is computing.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^
It may be that due to the off-axis design of this telescope, the wrong
reference height was used.  I did not choose one explicitly.  I don't even
know if OSLO (or in this case OSLO EDU a.k.a. OSLO LT) allows you to choose.
I choose to ignore this particular plot because I don't know what the
program is computing.  

I can't believe that there would be a 10000% (i.e. 100x) distortion from
some reference, if the reference were chosen correctly, given that the scope
has been constructed and that David Stevick and others report on its
excelent performance.
Don


-----Original Message-----
From: Michael Lindner [mailto:mikell@optonline.net] 
Sent: Thursday, June 10, 2004 2:43 PM
To: Donald Good; ATM
Subject: Re: [ATM] RE: ATM Schiefspieglers in Oslo LT

On Thursday 10 June 2004 07:01 pm, Donald Good wrote:
> I sent the following OSLO evaluation graphs of 8" Stevick-Paul 
> telescope to ATMsite.org, but it was never posted.

Sorry it didn't get posted. I don't recall seeing it.

Anyway, it looks fantastic, spot-wise, but in the ray trace analysis, I see
the "distortion" has a bump near the center of field at 10000%! Do you know
what that means?

--
Michael Lindner
http://www.starastronomy.org *** http://home.att.net/~mikel
http://www.atmsite.org *** http://www.atmlist.net

_______________________________________________
ATM mailing list http://www.atmlist.net/