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Optical bench design

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#51 BGRE

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Posted 17 June 2018 - 11:59 PM

Preferably without the typos (now corrected).

One method is to measure the wavefront error of a perfect sphere and use these results to correct the measured wavefront error.
Additional software is required to do this correction.

Since suitable perfect spheres are hard to come by and somewhat expensive its perhaps best to modify the setup so that the wavefront errors of the setup can be measured using lower cost methods.

#52 ToolMayNARD

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Posted 18 June 2018 - 02:48 AM

Hello to all,

I read all of you replies and will analyze them in detail later. Thank you very much, lot of useful info.

I noticed in the Edmund optics catalogue that plate beam splitters are offre also in 1/10 wave precision: https://www.edmundop...-beamsplitters/

Are they worth the cost? What are the drawbacks of a plate beamsplitter compared to a cube beamsplitter?

Cheers

Mauro

#53 BGRE

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Posted 18 June 2018 - 04:57 AM

Using a tilted plate beamsplitter in non collimated light adds coma and astigmatism to the transmitted beam.
Whilst the equivalent Zernike term amplitudes can be calculated the SHWFS software includes no means of correcting for this.
You'll also come across pellicle beamsplitters. These are fragile and have significant aberrations due to film thickness variations etc.
It is possible to design corrector elements for plate beamsplitters to correct their aberrations but these would be custom items.

It would be better to use a beamsplitter module (beamsplitter + lenses and source) that can actually be calibrated in a DPAC setup and use an external program to correct the measured telescope wavefront.

Alternatively the SHWFS could be used witha distant artificial star/ point source with fewer issues apart from the SA due to the finite object distance.

#54 ToolMayNARD

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Posted 18 June 2018 - 11:36 AM

Thank you BGRE. So cube beamsplitter is the way to go.

Bests

Mauro


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