Collimating front lens on a refractor telescope

Note: This only works with larger refractors which have front push-pull collimation screws connecting the lens cell to the telescope tube. It will not work with smaller refractors which have a screw-in lens cell.

Instructions: You will need a Cheshire eyepiece with a 45 degree angled reflective plate inside. Place a lens cap on the telescope, and put the Cheshire eyepiece directly into the rear of the focuser. Shine a torch or lamp into the side opening to illuminate the 45 degree silver plate on the Cheshire. Peer into the small opening at the rear of the eyepiece. You should see one or more small faint circles which usually overlap each other. Adjust the objective mounting cell’s push-pull screws, until the small circles merge into one. Tighten the collimation screws and re-check.

It helps to use an Altair GPCAM mounted behind the Cheshire eyepiece with the optional 120 degree meteor lens so you can adjust the telescope whilst viewing the screen. Turn the gain up high to see the image clearly. The camera does not need to be perfectly aligned to the Cheshire or connected to it, but it does need to show the image through the hole in the centre of the screen. Use the digital reticule on AltairCapture to place the crosshairs on the centre of the hole in the Cheshire and the zoom feature to magnify the image of the reflections. You can mount the GPCAM using the GPCAM tripod mounting.