I have recently acquired a Takahashi Mewlon 250. This design (Dall-Kirkham cassegrain) is known to be a very sharp narrow field instrument. For visual use Takahashi states a usable field diameter of 21mm. When I use a 2"
55mm plossl (46mm dia field) the outer 50% of the field is out of focus. This is mostly due to field curvature since I can sharpen it up by refocusing. I think with a well designed zero power field flattener/corrector with around 150mm backfocus (for 2" eyepieces) this scope could be a superb deep sky performer as well. This would result in a sharp field of about 1 deg. Any thoughts on how to make a suitable lens assembly?
55mm plossl (46mm dia field) the outer 50% of the field is out of focus. This is mostly due to field curvature since I can sharpen it up by refocusing. I think with a well designed zero power field flattener/corrector with around 150mm backfocus (for 2" eyepieces) this scope could be a superb deep sky performer as well. This would result in a sharp field of about 1 deg. Any thoughts on how to make a suitable lens assembly?
