I use an external guidescope and camera to guide the PlaneWave CDK 12.5 at AstroCamp. The initial set-up using a 60mm F/3.8 guidescope and Lodestar guider did not provide enough precision to guide the CDK 12.5 operating at F/8 with a resolution of 0.73 arcsec/pixel. When autoguiding with MaxIm DL it is recommended that the guide camera has a resolution of 1/10th of the main camera. The resolution of Lodestar and 60mm guidescope was 15.2 arcsec/pixel.
The image shows the upgraded guiding system now in use at AstroCamp. It uses a Telescope Service 80mm F/4.1 mini-refractor and Atik 314L+ guider. Note the flexure-free mounting using ADM hardware and hose clips – thanks to Steve Cannistra for the idea. The resolution of this set-up is 8.1 arcsec/pixel - much closer to the 1/10th plate scale ratio difference recommendation. The Atik 314L+ CCD makes a great guider. It has set point cooling, very few hot pixels and a larger field of view than the Lodestar which guarantees picking up a suitable guide star. When guiding with MaxIm DL and ACP using the Atik 314L+ it is necessary to use a custom ST-4 compatible guide cable to switch the X and Y axes. A wiring diagram for this custom cable can be downloaded here.