When the pixels of a guide camera becomes small and QE becomes high, you may not need a big guide scope, smaller pixels can detect the guide error in a shorter focal length. And, when the focal length is reduced, the FOV becomes larger, so it is easier to find bright guide stars.
QHYCCD’s new MiniGuideScope is based on just this idea. The QHY5L-II has 74% high QE, 4 electron readout noise and small 3.75um pixels. This camera is idea for a short focal length guide scope. The MiniGuideScope is a 30mm f/4.3 (130mm FL) ultra-small telescope. It has no complex focal adjust system. Just rotate the front of the OTA and it provides fine focal adjustment. Once focus is achieved, the tube can be locked into position and there is not need to focus again unless the system is moved.
The MiniGuideScope provides pin-point star images as sharp as any lens in the industry.