Review on AmScope CA-NIK-SLR Nikon SLR / D-SLR Camera Adapter: Enhance Microscopy with Seamless Compatibility by Bryan Fisher

Some of the negative reviews had me worried about this product but I found it worked pretty well once you understand what it is and what its limitations are. MUST be used in manual mode. Communication between it and your camera is absolutely zero. There's no aperture control here, and you're focusing with a microscope, not a camera. Once you understand this, it will be very easy to use. Focus with your microscope's eyepiece, replace the eyepiece with this adapter and your camera, adjust the microscope's focus in real time via your camera's screen, choose the appropriate exposure and take the picture. For my Amscope and D5500 setup I found 1/40 and ISO 100 to be a good starting point. You may have to take a few shots to get the exposure right, but they're free.