Optical metrology

This section presents public astronomical equipment test reports.

Starting on November 2015, report will be presented in French and English. For older reports that are only in French, please see the first bilingual report that contains the same type of measurements.

Usually those reports present the following information:

– Lyot test picture (reflectors only) : qualitative overview of the high frequency defects (ripples) of the primary mirror surface

– Wavefront map featuring PTV and RMS errors in several wavelengths (if refractors, otherwise measures are done at 635nm)

– PSF (Airy spot) with its dimensions and Strehl ratio (corrected at 0% obstruction)

– MTF with theorical cut frequency

– Focusing shift over wavelength (longitudinal chromatism, compound and refractors only)

– Spherochromatism (compound and refractors only)

– Sometime spherical aberration over color or backfocus

– field curvature and full light cone size

– Spot diagram up to 21mm from the axis, with and without field curvature (visual and CCD applications)

Note regarding best focus results :

New reports since 2013 mention the best focus wavefront error (WFE) in addition to the raw WFE.

The HASO delivers WFE at the null curvature focus position. In that sense, it’s a raw measurement as focus is not meshed with 3rd order spherical aberration. Although it is the good measure to evaluate precisely the optical performance versus its theorical ZEMAX design for example, it doesn’t reflect perfectly the real utilization on the field.

For visual or imaging utilization, the focus is done at the best focus position, the position that delivers the best result (minimum PSF size).

If some spherical aberration is present, part of it (about one third) can be compensated with some defocus. The best focus result takes that into account and it is the best position in real usage.

Astro-Physics

– Astro-physics Starfire 130EDF #1 #2 #3 #4 #5

– Astro-physics Starfire 155EDF #1 #2 #3 #4 #5

Alluna Optics

– Alluna Optics 410/4 #1 #2

Altair

– 102 F6.5 triplet

APM

– 80/480 triplet

– 107/700 Triplet

Astroprofessional

– 102/714