Trinocular microscopes are binocular microscopes with an addition port for a camera.  The camera port will require a camera adapter before you can attach your camera.  There are a number of different types of microscopes which have trinocualr heads, a sample of them is shown here.  The best type of camera to attach is a microscopy c-mount camera because this is what all trinocular microscopes are designed to take.  This also means that the c-mount adapters are readily available, inexpensive and will give predictably good results.  You can attach other types of cameras often with excellent results but the adapters are rarer, the outcome is difficult to predict and they are more expensive and non-standard.

Trinocular heads come in two forms, one type has a lever to switch the light to the camera and away from one or both eyepieces, the other type have the image permanently going to both the camera and eyepieces.  Whilst the latter is appealing it does mean that the available light is therefore shared and, where illumination is affecting the camera’s performance, it might not always be desirable.