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Thanks for al the positive comments everyone.
@Markus,
The lens is native f2.8 and with the lens wide open there is significant star distortion around the edges of the field of view. By experimenting with different f stops I found that I had to stop it down to at least f5 or more to have a satisfactory image. Further to that, I don’t like the diffraction effects that come from the lens iris so rather than stopping the lens down with the internal aperture controls, I leave the lens iris wide open and use step down rings on the front of the lens to reduce the aperture. The set up that I’m using now has a 37mm step down ring resulting in a focal ratio of 200/37=5.4. This calculation would be approximate due to the fact that the step down ring is in front of the lens but is close enough for my estimations.
Also, to respond to your observation re how to control the lens iris with no camera attached. This can be done actually as I am using the Astromechanics adapter which provides the mechanical connection between the 6200 camera and the lens and also includes the electronics to control the aperture and focusing. I don’t use the aperture control but do use the focus control so that auto focus is possible from my image acquisition software (SGP Pro).
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