# Knowledge Corner

SpotOptics is pleased to present information on the principles of their wavefront sensors and wavefront sensor based systems. You can learn more on Zernike polynomials, Shack Hartmann wavefront sensor comparison with interferometers, aberrations and photo gallery on aberrations. FAQ on SH test is also available

## Exceptional accuracy and precision of our Wavefront Sensors

SpotOptics Shack-Hartmann wavefront sensors results have been compared with results from the most popular interferometers : Zygo, Veeco, Fisba, 4D Technology

## Questions on Shack-Hartmann test

### What is the Shack-Hartmann test and how is it different from the Hartmann test?

It is an extension of the Hartmann test. In the Hartmann test, a screen with holes is put in front of the primary mirror, and a photographic plate is placed near the telescope focus to record a pattern of spots. An analysis of the position of these spots gave the aberrations of the telescope.

## Importance of using lenslet arrays with long focal length

#### Shack-Hartmann image of aspherical lens fl=50mm taken with OMI lenslet array fl=22mm and fl=11mm

 Shack-Hartmann image taken with OMI-22 (lenslet array with fl=22mm). The diamond turning marks are clearly visible Shack-Hartmann image taken with OMI-11 (lenslet array with fl=11mm). The diamond turning marks are hardly visible

## Zernike polynomials in SenSoft

 Zernike polynomials used in Sensoft – our wavefront sensor software Zernike polynomials represent a particular phase aberration W  at a point P on a circular pupil and they are generally expressed in terms of the normalized radius r of the  pupil and  the  azimuthal  angle φ,  by the following expression:    rn cos (m φ + φ0)