Inside Focus

Inside Focus

Outside Focus

Outside Focus

Eyepiece: 6 mm Zeiss Abbe ortho EP (411x magnification)

“This is a triplet Super-ED Apochromat , airspaced and fully multicoated.
The starimages show no false color at all. The inner fresnel rings show a very minor difference due the a minimal amount of chromatic aberration. The outer rings are equal and show an extremely smooth lens which is confirmed by the interferometrical testresults above. This lens is made near to the theoretical and practical limits”

Markus Ludes (APM-Telescopes)

This test was done on an inside focus image (green-channel). Although many rings are visible, being a refractor means that counting the rings (in a well-corrected instrument) is nearly always a clear guess of the amount of defocus. In this case the defocus was just over 4 1/4 waves. The well defined structure of the diffraction image made simulation rather easy. About 1/10 wave undercorrected LSA and 1/10wave overcorrected HSA seems to be present. The total wavefront error therefore would be around 0.16 (1/6) PTV and 0.035 RMS (1/29). Both are not in agreement with the interferometric test-report so the testprocedure is clearly not flawless.

Cor Berrevoets