5 stars for optical performance, I have compared this eyepiece against an Orion Epic 5.1mm and a combination of 2.5 Televue powermate with 13mm Nagler T6 (resulting 5.2mm and the Hutech 5mm shows clearer and sharper images. It shows great detail on my Unitron 75 f/16, on a friend Televue 76 (using a 2.5 powermate,and even more detail on a friend TMB 80mm f/6 apo Signature series, all at 240X!. This is a great eyepiece. The only downside is the little tiny hole where you observe, but I guess that is the price you pay to get the sharpest view. It may be the sharpest eyepiece under $300. I think I will buy also the 6&7mm.