I would say indirectly. For a Cassegrain if your secondary is perfectly centered, then the centering of illumination can tell you if the optics is collimated. However, if your secondary is not perfectly centered, say off by just a few millimeters, you can still
be perfectly collimated (if your secondary mirror is spherical) but in that case the field illumination will not be centered.
There are many other factors too. The uneven illumination can be caused by your filter, and the camera sensor tilt and displacement, etc. I have a perfectly collimated iDK but the illumination is never dead centered.
