[Oscar in Bin (John)]

I hope to be the proud owner of a new CCD camera shortly and want to make sure I have the hardware set up properly. I want to run the camera with a flattener, a reducer or an extender/flattener. I want to check the distance from the back of the flattener etc to the plane of the CCD as I understand this is critical in getting a good quality image. This will help me order the necessary spacers.
Can someone point me at where I might find this info for a Takahashi refractor. Also what tolerance is there on this distance.