[Dennis]

Originally Posted by janoskiss

John, I read it on the Baader Hyperion brochure or "data" (uhm advertising) sheet:
http://www.alpineastro.com/Eyepieces.../Hyperion2.pdf
which says that if you remove the barlow bit, the negative achromatic doublet, you end up with a 6-element Erfle.

Last night, with the 21mm Hyperion in the WO 80mm, the FOV was pleasantly sharp all over. When I unscrewed the (1 ¼”) Barlow, making the 21mm Hyperion it a (2”) 42mm, the view was only sharp in the central half of the FOV. Outside that circle, the stars were quite fuzzy. This was all through a WO 2" Dielectric diagonal.

Its worth noting that I am not a visual observer by nature, so my review of eyepieces would tend to be relatively unsophisticated and not supported by lots of hard experience.

Cheers

Dennis