According SIMSPEC SHG version V1.6, by Ken Harrison the theoretical result of X/Y ratio 1 should be 4.43ms or 225fps for my set up : TLAPO60/360 f/6 with ASI290MM and scanspeed 16x.
When lowering the speed form 3.38 to 4.04, the shape moved from an ellips towards a circle. Not yet perfect but it proves the theory.
