My Homemade Newtonian Telescope has a new problem.?

F3.6 is very fast. It may well be Coma error...where the fcous is only exact at the centre of field of view. So small objects may look fine but extended ones (saturn?) may be distorted..see what Jupiter shows. you will need to collimate very well, and every time you use the scope...letting it cool down for an hour or more etc etc. Also check the collimation of the collimator! These can be quite a bit off. Better to use a high power eyepiece and a bright star and adjust so the "rings" are symmetrical as you focus eather side of exact focus. You focus motion also needs to be pretty smooth as it moves and no wobble or thsi too will change the collimation, making it a function of the exact focus position. Its the pain of having such a fast scope, which is why they are not often made commercially. good luck!