Matt,
I'm not sure if I'm following you. You mention you enjoy imaging planetary nebula which on average are small in angular size, thus requiring a considerable focal length. This would rule out a wide field APO. Have your imaging goals changed? Do you want to do more wide field work? Typically anything under 1000mm is wide field (some would say 1500mm). I'd consider deep space going beyond 2000mm (equipment demands of DSO imaging are considerably higher). Of course this is open to interpretation.
Quote:
Originally Posted by beren
I"ll zip in and mention the Pentax range of refractors {in hope of feedback about them  } |
I've had the pleasure of using the 100 SDUF Quadruplet APO. At F/4 its a very quick scope and fun to use. It provides a large flat field and vignetting is keep to a minimum with its 88mm image circle. Actually, its optical configuration is a copy of the legendary Takahashi FSQ created by Yuyama-san, thus has similar characteristics. The SDUF is poor scope for visual work, but outstanding for imaging.