Glad to see someone reading the optics calculation page. The calculation for the infinite conjugate is much simpler. The distance between the tube lens and the objective is not important as the light should be focussed at infinity. The distance between the back face of the lens and the face of the camera should be the back focal length of the lens. You can check how well this is focused by taking the optics module out of the microscope. Removing the objective. And taking an image of something far away (perhaps aim it out of a window and look at a tree). Is it in focus? If it is not you may need to shim the camera. If it is out of focus on one side this would mean the sensor itself is tilted.