Tonight I did some test imaging of Comter Tuttle through the 400mm lens with a 2X teleconverter making it a 800mm F/5.6 system. Continous 1 minute exposures were made from 01:54 UT to 02:35 UT on December 27th. Below is the sum of thirty seven one minute exposures. The comet is moving quite rapidly in dec (about 7 arcseconds per minute) thus the image of the comet is trailed against the stellar background.
Details: 37 minutes (effective) @ ISO 1600 | F/5.6 | 800mm | Takahashi EM200 Mount
Details: Comet centered sum of 37 images.
Details: Cropped and inverted version of comet centered image