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Very interesting discussion and I really enjoy reading what everyone has to say about the topic. Colin, I certainly prefer the look of the image taken with D7200 - and both indicate quite a few interesting regions for potential targets! As you can probably imagine, I really can't wait to finally test my new small refractor and see if it is capable to collect photons more elegantly than the best telescope I have owned until now - a TS 4" doublet.
As for spot diagrams for apochromatic refractors, below is an interesting excerpt from an article written by Pal Gyulai, optical designer from CFF Telescopes. I hope it is okay to quote entire paragraph.
In fact, if we construct a fast triplet APO lens of F/6 focal ratio and the optical design is optimized for the "best looking" spot diagrams, then after actually building the lens and testing it under the sky, the image quality will not be optimal. This is not surprising, as the classical method cannot be used for optical systems approaching (or at least getting reasonably near) the diffraction-limited quality. Today we expect better than diffraction-limited performance everywhere between the blue and red colour wavelengths, so, the classical methods (that can't explain why we see an Airy disk surrounded by diffraction rings in the eyepiece) cannot be used anymore. This methodology was perfect to design car headlights, room lighting and slow focal ratio achromat lenses and (judging by today’s standards) semi-APO lenses. But it is not usable to construct modern, fast APO systems.
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