Posts Made By: Paul Krumenacher

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?

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?

I am new at planet imaging. This is my first attempt.

Mewlon 250
2X barlow
Toucam pro
1950 frames in Registax

Paul Krumenacher

Allen:

The M250 has 96% mirror coatings. So
9.8425^2 - 2.8346^2 = 88.8396
SQRT 88.8396 * 0.96^2 = 8.69" effective aperture.

Paul Krumenacher