Video courtesy "Innovations Foresight" our North America partner and reseller

This product is intended to measure accurately optical wavefront (> λ/55) coming from telescopes, refractors or any optical setup.

Or said more simply, it measures the optical performance of optical systems, based on Shack-hartmann wavefront analysis.

The product comes with a 5 megapixel camera and microlenses array, a visual aiming system and a set of collimators to acommodate with F/ number from F/3 to F/20. The next picture shows the uncooled version of the Shack-Hartmann. 

Measuring optical performance of a low cost Kepler newton F5 dobsonian telescope using a star.

Measuring telescopes and refractors optical performance with a flat mirror (Testbench tests).

System specifications

The next video is showing how to use this device

This system can be inserted into a 2" eyepiece holder / focuser, and It has an reticle eyepiece allowing star or source centering.

A reference pinhole comes with this product to calibrate the shackscope.

The idea is to get the resulting system wavefront in a simplest manner.

Three application cases are presented hereafter:

A low cost Kepler 12" dobsonian telescope has been tested. This telescope has no tracking capabilities so the polaris star has been used.

This is a magnitude 1 star, and this is possible to use it this way, because the star motion is very slow. Seeing/turbulence effects can be canceled out by the software so that only optical performance is measured.

The 40x40 shackscope was inserted into the telescope's focuser and the latter was aimed to the polaris star. This shows that even a very low cost system can be measured that way without any problem.

This telescope showed, after shack hartmann analysis, a basic astigmatism issue, and has a wavefront error performance of 126 nm rms. (λ/4.4 rms)

The strehl ratio is only 17%. To know whether it comes from the mirror, or from the mirror cell, another test needs to be performed by rotating the mirror by 45°

Measuring optical performance of a 10" RC type telescope

Advanced users or telescope resellers are using this setup. The telescope is put the front of a flat mirror. The mirror diameter exceeds the telescope diameter, and has a very good optical quality. This is called double pass tests, and the optical defaults from the telescope to test are multiplied by 2

The software can instantly delivers wavefront analysis, so that the telescope can be collimated and his quality beeing measured.

ALCOR-SYSTEM can deliver the whole set, including reference source, beam splitter , optical large flat mirrors. For such setup please contact us, so we can provide the quote for you of such a system.

On the other side, the shackscope 40x40 is installed to the telescope, and an additional pinhole source and beam splitter is used.

The ALCOR analysis software allows to remove the astigmatism, and displays how the mirror would perform without astigmatism

This is quite spectacular to see that the performance is now around 23 nm rms, and 92% strehl ratio can be reached.

This system has been validated and its performance compared with a very expensive metrologic interferometer from ZYGO, corp.

The shackscope 40x40 tests have been achieved by

Results are totally similar with Zygo tests, showing this tool capable of very accurate wavefront measurements.

The next telescope case, is a Ø 10" (254 mm) F8 RC type telescope. The origin of the optics is not known.

The 40x40 shackscope has been installed at the 2" telescope's output.

Wavefront map of the telescope optics

Point Spread Function of the telescope optics, astigmatism is really disturbing

Please, tell us what F ratio you want to be able to test/measure.

The next image shows from the camera the spots pattern, and also the central obscuration of the large secondary mirror.

Despite that fact, the software can compute the wavefront error.

The modal analysis (based on zernike polynomials) is showing a significant spherical wavefront error, that is really impossible to spot by naked eye.

The 213 nm wavefront spherical error is mainly due to a small distance error between the primary and the secondary mirror and can be fixed easliy by changing the distance.

The mirror distance has been increased by 4 mm and strehl ratio could increase from 28% to 70%

The shack hartmann helped to improve the performance

1"3/4 filters can be inserted, so that measurement can be carried out at different wavelengths

All images from Optique Unterlinden facilities.

Collimator can be detached and exchanged like the following image

We are open to custom designs. This product has been used for ophthalmology application.

Windows 7,8 and 10 software is available here, simulation mode can be used

To carry out such a test, a beam splitter is required.  ALCOR-SYSTEM can provide a 50-50 λ/8 PTV 25x25 mm beam splitter cube. Since the pinhole is very close to the cube only 12.5 mm is used and surface accuracy is better than λ/25 PTV (checked with Zygo)

This apparatus works with F/ ratio as low as F/4, and a F/3 is also available on request. 

Measuring mirrors during parabola figuring at center of curvature

It is possible to use this system to check parabola figuring at center of curvature, like this is achieved with a classical Foucault knife test. Say, for instance, a 400 mm F5, the test is carried out at 4m from the mirror, in the lab without any other optical device (no flat mirror).
In that case, the massive spherical aberation can be cancelled out, and thanks to the shack-hartmann dynamic range, the residuals defects
of the mirror can be spotted when it is figured, even with no aluminum coating. The next table shows for each diameter the F/ range that can be measured with this system. For lower F/ please contact us.

150 nm of 1st order spherical aberation is visible, as well as 210 nm of second order. The total performance is 110 nm rms, that is not so good. Nevertheless, no astigmatism is visible, that is impossible to detect with a classical knife test.

To be able to perform this test, a pinhole source, and a beam splitter used above in case #3. The nex plot shows the error profile and
where the glass needs to be removed.

As a test, a 200mm F4 was checked at center of curvature (i.e at 1600 mm from the mirror), and this is the result:

A ring to mount a M28.5 color filter can be inserted between the collimator and the shack hartman body, in order to perform measurements of sphero chromatism, or any aberration that has a wavelength dependency.  This ring is provided as a standard part.

Dynamic range for some aberrations

These figures are computed with a projected pupill diameter on the microlens equal to Ø 4.3 mm

A cooled version of the camera sensor that performs the analysis is proposed, allowing long exposures (say, 2 to 5 minutes). Instead of an eyepiece, a sighting camera can be installed (camera on top) for both systems (cooled & uncooled).

A cooled version of the camera, allowing long ewposure is also proposed, contact us for more information.

Cooled Shack Hartmann with 2.4m NARIT Thai Telescope

The national THAI observatory ordered by us a cooled 40x40 Shack Hartmann device, in order to characterize and collimate on Sky their 2.4 m AltAz telescope.

A new field corrector must be installed and its performance evaluated with our Shack Hartmann.

Please hereafter is the publication about this corrector and how it has been characterized with our shack hartmann

© ALCOR SYSTEM