It was late when I posted, I got my arcminutes confused with my arcseconds. Yes, I'm speaking of arcseconds! The Obsession specs are 2060 focal length +/- 50mm so everyone's 18" scope is a little different. I also raised my primary a full inch to achieve the shortened focal length needed. I know some Obsession dob owners are struggling with their mallincam by posts on the Yahoo discussion group. The Mallincam chip is a 1/2 inch CCD 811 x 508 pixels.
According to my SkyMap Pro, M101 is about 27 x 28 arcminutes in size, so I guess it depends on how far one goes out on those faint, faint spiral arms.
Tonight, I just pulled out the Evo 30 for the 1st time this year. The collimation is spot on, which I know it should be, but there's always those anti-collimation gremlins that hang around dob's…