Had my first attempts using the Sigma 300-800mm lens with a Sigma 2x converter tonight. I belive that any failings with the image are my fault and not the equipment. Not to shabby I feel for first attempts.
Moon shot using Nikon D300 with Sigma 300-800 plus Sigma 2x Converter. Taken at f11 at 1/200 secomd. Lens set at 650mm which equates to about 1950mm equivalent focal length with crop factor and converter.
Image is slightly cropped and very slightly sharpened in Nikon Capture NX