[Stefan Buda]

I've been making Corrected Dall-Kirkham astrographs commercially for a while and prospective buyers often ask if the instrument is also good for planetary imaging. Unfortunately I have to disappoint them by explaining that the 50% linear obstruction, while perfectly ok for deep sky imaging, disqualifies the CDK for planetary imaging.
So I decided to design a complementary instrument of the same aperture, that is as good as theoretically possible for planetary imaging.
The case for the Dall-Kirkham:
My main criteria in deciding the type of instrument were, aperture, focal length, secondary obstruction size, thermal behavior, portability and maintenance (collimation).
The aperture had to be set at 250mm as that is the maximum I can manage with my equipment.
Focal length for this aperture needs to be around 6000mm for imaging at the theoretical limit, but that would mean an f/ratio of 24, quite possible but not very nice from a manufacturing point of view.
A typical SCT telescope has a linear obstruction of at least 32% and I wanted to do a bit better than that.
Thermal behavior means that the instrument needs to track ambient temperature changes well without trapping warm air or cooling too easily below ambient and getting dewed up.
Through portability I mean a weight of not much more than 10kg so that the instrument can be taken to locations for catching planetary events or avoiding local cloud.
Ease, and retention, of collimation, and also focus drift, can be dealt with using carbon fiber and precision mechanical construction.

All the above criteria come together nicely in a 250mm f/16 Dall-Kirkham OTA.
One other very important aspect in favor of the D-K is that the optics can be made to a very high standard, rivaling the venerable Newtonian. This aspect is a bit hard to explain for people other than mirror makers.