I built my rig to use my 400mm lens. Tried it out the other night with some long (10 minute) exposures. I was slightly off with the polar alignment but overall the rig worked great. This is 6 10 minute lights and 6 10 minute darks. Stacked in DSS processed in Ps. Need to add another 6 or so subs to clean up the graininess in the areas where there is thin hydrogen clouds. But overall I'm very pleased with everything.