Since most of the microscope cameras have much narrow view angle than the oculars a reducers are frequently used. In my case i have an Amscope SM-4NTP that come with a camera adapter and Hayaer HY-6110 camera . The original adapter fit well with a 0.5x reducer, but it's field of view is still too small and elevate the camera well above the microscope.
To achieve a wide field of view i decided to use a 0.35x reducer, as bonus it's much shorter than the 0.5x and have it's own focus ring.
Since this reducer eliminate also the original camera adaptor to have it focused both the camera and the oculars become impossible task. To achieve a proper focusing additional distance of approx. 28 mm are required between the microscope and the reducer.
To solve this problem i design a simple 3D printed spacer. Since i do not consider direct threading in 3D printed part as an option, i add two pockets for a M5 T-slot nuts.