Here are comparisons, first in blue, from full aperture/no Chromacor to 7"aperture/with Chromacor U1 and then at focus in green between the full aperture sans Chromacor UI and stopped to 7" with the Chromacor UI.
The lens is indeed, decidedly more civil in SA performance (meaning straighter lines) stopped to 7" + the Chromacor than at the full 8" aperture without the Chromacor.
What's not shown though is that with the 7" stop and Chromacor in place, when I focused to the green null you see in the picture and then carefully and precisely changed out the green LED for the red and blue ones along with their matching color filters (all the same brand), I was still seeing nulls in red and blue. This means all three colors were focusing pretty much on top of each other. Without the Chromacor in place, the red and blue focused measurably further out than green by maybe 5 to 6/64" or so.
So here you have non subjective proof that the Chromacors really do work when properly implemented. They not only reduce the longitudinal CA (due to focus differences from red to blue) but also the spherochromatic contribution to CA (the changes in spherical aberration from red to blue).
I have a feeling that, once I get the scope out under the stars and a good view of the Moon, and barring any significant astigmatism and coma, the views at 7" aperture with the Chromacor U1, though dimmer, will be considerably sharper and with significantly less "CA" that at full aperture without the Chromacor.
Another great use for DPAC!
Edited by Jeff B, 16 January 2020 - 06:40 PM.