This test is with the reducer mounted and with the CCD positioned 4.25" from the back of the OTA. The mounting is with the AP SCT adapter alone (no additional spacer). The reason the distance ended up at 4.25" (and not 4") is the FR was stopped by the field stop inside the OTA that protects the correcting lens. Note elongation in stars in the corners - but noticeably less than at 6".

Again, the FR was mounted on the camera at close to (+/- 2mm) the Antares specified 79mm distance.

Since the FR was inserted into the OTA as far as it would go, this is the closest the FR/CCD combination could be positioned to the OTA. So, a shorter SCT adapter will not help. The only recourse is to shorten the 79mm distance between the FR and the CCD plane, which will decrease the reduction factor, i.e., from 0.5x to something like 0.62x - which would be acceptable, of course. See next frame.