I performed the tests on Wega and mostly Altair ( more comfortable to observe:-) I used my Leica WW ASPH Zoom 18 mm for lower magnifications (42X), the same Leica with Zeiss barlow for higher magnifications (190x) en my Pentax XO2.5 for highest ones.(290X)
The lenshood has an extra central opening of 110mm. One can choose to observe with the full 150 mm or the 110 mm opening. In the last case it becomes a
Low magnification (42X)
- BBHS mirror.
The colored halo at the size of 11X the Airy disc was blue.
Scattering was present but moderate.
- Zeiss prism.
Halo was not noticeable smaller or intens.
Scattering seemed a tad less.
High magnification (190X)
- BBHS mirror.
Halo was noticeable less then at lower magnification. Less blue, far more moderate, seemed shifted to gray. Same size as at 42X. Slight orange / blue rim around Airy disc depending of eye position
Scattering was bigger than the faint blue colored halo, moderate though and gray.
- Zeiss prism
Halo seemed noticeable less than with 42X. Seemed shifted to gray. Same size as 42X. Slight orange rim / blue rim around Airy disc depending of eye position. Scattering a tad less intens than with mirror, but same size.
Highest magnification ( 290X)
In both accessoires the blue halo had almost turned into gray, except for a slight blue /orange somewhat irregular rim around the Airy disc ( Not the first diffraction ring), depending on eye position. I suppose I described Spherochromatism here. I could not see the difference between a colored halo and the scattering any more. Scattering was a tad less intens in the Zeiss.
We are talking about marginal differences though. Only visible at a direct comparison when accessoires can be changed quickly. The differences in intensity in halo and scattering could only be established with the star outside the field! With the star inside the field its brightness overwhelmed all differences. Edges of in-and out focussed stars could not help me any further.
At what magnification was the transition from blue to gray and at what magnitude?
Did the presence of the grayish halo have effect on the observation of let's say double stars?
It did not on double star SAO 84572, magn. 7 and 7.8, separation 1,2". At 190X I could see them both with ease, clearly separated, with a small dark split between them. Delta Cygni, magn. 2.9 and 6.3, separation 2,8" was clearly separated, never seen it like that before, but one could see a slight gray halo around the main star. I can imagine that Sirius B would be more difficult....