von Struve and STT doubles discovered by his son Otto Wilhelm von Struve. few of my exposures lasting as long as five minutes showed elongated stars. Imaging For those looking at the Mark III as an imaging platform, there are a few things to consider. As mentioned before, the strain-wave drives have zero backlash, which is an incredible advantage for guiding the mount whether you're old-school and do it manually (I did it just for fun) or autoguide. And in the case of autoguiding, you must use a system that controls the mount through its Wi-Fi or USB computer connection, as there is no ST-4-compatible-guiding port on the mount or hand control. I had excellent success using PHD2 mentioned earlier (downloaded for free from openphdguiding.org), which was all the more noteworthy because I had no prior experience using the software. The bigger issue with using the Mark III for deep-sky imaging is its periodic error. Like traditional worm gears,http://www.openphdguiding.org