There're many discussions on other forum about SCT's actual focal length depending on visual back setup and Baader GPCs' actually magnification factors. As it was a cloudy weekend, I took the chance to do some measurement to get some hard data to get better understanding of it. 1. The setup: A yardstick on a table in the garden some 22meters away from C8, some combinations of my visual back setup are measured: 1.1 The stock 1.25" visual back Despite its cheep shap