Mike_

Hi, Having spent many hours trying to collimate my RC6 I found the 2" focus aperture (draw tube?) had issues. If I place an autocollimator in it, the secondary mark is off centre. Using a Cheshire with 2" to 1.25" adapter its in the centre, a laser would return down the centre also. (both of these failed the star test) Placing the camera assembly in it, using the collimation where the mark is off centre was actually the correct one. If I collimated so everything was in the centre the star test would result in oblong out of focus stars. This has driven me nuts for a month, I emailed GSO and they said the primary to secondary mirror should be 286mm. Nice to know but impractical to measure even with a 3D lidar (tried that). - While using the autocollimator I noticed if it was inserted with slight slide pressure (same as camera weight?) everything would be spot on in the centre. It still isn't brilliant, the back focus maybe out since Im also using a 0.67x reducer which is more like 0.64x, or 883mm - No spacer rings are used between scope and focuser. A 5mm ring Ill test after the reducer. Image of M45 attached with the current collimation. Camera is the ASI178MC. It helps to print a set of concentric circles to act as a reference when bench collimating the RC. - After initial Cheshire secondary mark alignment, Laser primary, check with Cheshire and finally the autocollimator. The autocollimator will show the circle set reflecting back. Annotated images from the various tools attached. - Still work in progress... Update: The ASI CCTV Lens in its holder inserted into the 2" focuser with ImageJ and the concentric circles plugin shows the alignment, shame this doesnt run on a realtime video feed. Ive asked the author of AstroDMX if the reticle position can be changed for this purpose.