Virtual Couder Screen

[Hans-Heinrich]

Hello,

my name is Hans-Heinrich, I live in Austria/Europe.
Please let me draw your attention to a software that I have recently written: VCS-Virtual Couder Screen - Version 2
When parabolizing my 350mm 1:5.8 mirror some years ago I decided to use a webcam in order to display the Foucault shadowgrams on a computer's display. This was very comfortable but I was not satisfied with the commonly used couder screens positioned in front of the mirror. All those problems with difraction in small zones, difficult brightness-comparison of related zones, the great number of visible zonal apertures and so on.
This is why I wrote a software that emulated couder screens directly on the computers display. There was no need to have a real mask any more! The software really worked very well, as there was of course no diffraction at all and thus I could realise very small zones.

Recently I have improved the software. The most important new functionality in this Version is 'Auto Compare', providing a fully automatical real time comparison of zones - much more exactely than a visual comparison!

Other benefits are:
- Automatical comparison of zone brightness exactely along the effective radius. A great advantage e.g. when measuring the outer zone. An eventually existing sunken edge is visible but it does not influence the measuring results at all.


'Anti Seeing' mechanism
Count of zones can be varied arbitrarily
Flexible zone radii according to Texereau, Couder, N.O. Carlin, Pin Stick plus free radius definition
Comfortable management of readings (automatic averaging)

If you are interested please watch this introduction video:
http://www.youtube.com/watch?v=mCI0J2ua2Xw

Here a video showing how 'Anti Seeing' works:
http://www.youtube.com/watch?v=nIbwSSVkY18

And here is the link to my website:
http://www.sonderloesungen-wenk.at/index.php?id=vcs (http://www.sonderloesungen-wenk.at/index.php?id=vcs)


Alois Ortner, a very well known austrian optician has tested VCS and writes in a german forum (http://www.astrotreff.de/topic.asp?TOPIC_ID=130724):

"VCS is fast and accurate. ... I was astonished when making repeated readings, could hit the center (I measure without a central obstruction) with +- 0.01mm, the zones with +-0.006 mm and the edge with 0.003 mm"

Greetings from Austria
Hans-Heinrich

[clive milne]

Nice work Hans-Heinrich,

I like what you have done here.
If I could ask a question; have you considered adapting your set up to show a synthesised or inferred null?

You could use software to build up an image of the entire optic using multiple images from different zone radii correlated to knife edge position.
This would of course require a motorised precision linear slide. Being that we are in the age of affordable CNC hardware, the electro-mechanical side of it should be pretty straightforward.

regards,
~clive.

[Shiraz]

Hi Hans-Heinrich. Really interesting - thanks for posting this information. Regards Ray

[Hans-Heinrich]

Hello clive,
interesting idea! I have to think about that :screwy:

[Hans-Heinrich]

Hello,
I have now released version 2.1.0 of my Program 'VCS-Virtual Couder Screen'.
Most important new feature is an autómatic evaluation of measured values by longitudinal and transverse aberration as well as a surface error profile. Results are shown graphically and can easily be stored as reports.
Additionally there is a possibility of automatic optimization by minimal transverse aberration, the progress of which can be followed in the graphs.

It is important to mention that this evaluation is according to the algorithm used by Jean Texereau.
No doubt, this approach has its limits in terms of absolute accuracy, but - despite that - gives a good impression of the mirror's current quality and instantly tells the mirror maker where the surface needs further retouching. Looking at the optimized transvers aberrations graph you can immediately say if your mirror already meets the Raileigh Criterion and the wavefront error is less than Lambda/4 PV.

The benefit is that it's now possible to evaluate the mirror instantly within the application and not having to transfer the readings to other applications every time.

To my mind these evaluations are sufficient for a great part of the parabolizing process. When finishing the suface, it is of course recommended to transfer the readings to other evaluation programs that are specially designed for this purpose and thus deliver more detailed results (Strehl etc.) - not least to take advantage of the high precision of measured values provided by the Auto Compare Mechanism.


Furter informations here: www.sonderloesungen-wenk.at/index.php?id=vcs (http://www.sonderloesungen-wenk.at/index.php?id=vcs)

regards
Hans-Heinrich

[scopemankit]

This is a superb piece of software. I shall test it on a recently finished mirror and use it on a 10" I am polishing at the moment. How long is the trial period?

[Hans-Heinrich]

Hello Chris,
Thanks! Trial period is 8 seperate days.

[Hans-Heinrich]

Short information:
I've just released VCS-Version 2.1.2. Download here:
http://www.sonderloesungen-wenk.at/index.php?id=14#c360

2.1.2 contains a bugfix for incorrectly calculated absolute values of 'Surface Error Profile' and also incorrect diagram 'Transverse Aberration / Diffraction Disc Radius'. SORRY for that!!

But there also is a new feature:
VCS now calculates the 'Surface RMS Error' and additionally offers an automatic optimization for minimal RMS (just as other programs as Figure XP or FTA do)
Details here: http://www.sonderloesungen-wenk.at/index.php?id=vcs#c394

regards
Hans-Heinrich