Trinocular Photo Ports

Trinocular microscopes include a third ocular port intended to be used for attaching an imaging device such as a still or video camera. This photo port is a feature which can be found on compound microscopes and stereo microscopes alike. The benefit of a dedicated photo port is the ability to attach a camera without interfering with the front ocular ports which hold the eyepieces.

One thing to keep in mind when using a camera with a microscope is that the magnification seen by the camera is derived only from the objective lens, and does not include the compounding effect of eyepieces. For example, viewing an image produced by a 4X objective lens through 10X eyepieces would result in 40X magnification, but the camera would only see 4X magnification since it bypasses the eyepieces.

Switched Photo Ports

Switched photo ports require the use of a lever, rod, or some other mechanism to enable the photo port by shifting the light path from one of the front ocular ports to the phot port. By enabling the photo port, one of the eyepieces will be disabled. This is often referred to as a 100:0 or 0:100 port since 100% of the light is directed to the eyepiece or photo port while the other receives 0%. The advantage of this design is providing 100% of available light to the photo port when needed, therefore producing the best possible image.

Shared Photo Ports (Simul-Focal)

A shared photo port – also referred to as simul-focal -- uses a prism to split the light path which normally provides light to only the eyepiece, in order to provide light to both the ocular port and photo port simultaneously. The advantage of this design is that no switching is needed so a camera can be persistently active. The disadvantage is the diminishment of light reaching either port. Because the eyepiece and camera receive only a fraction of the available light, images are not as bright.

Stereo Microscopes

Stereo microscopes use two paired objective lenses to provide stereoscopic vision. Each objective lens provides an image to its corresponding eyepiece resulting in two independent optical paths. Most stereo microscopes use the Greenough design which relies on slightly tilting both objective lenses to produce the appropriate amount of separation. Because of the tilt, focus will not be even across the field of view for either optical path since the lenses are not perpendicular to the subject. When viewing an object through both eyepieces simultaneously, the left and right images are overlaid and compensate for the changes in focus. This does not, however, work for cameras.

A camera attached to any port will only see through one objective lens, so any offset in focus caused by the lens tilt will be evident. The changes in focus will vary depending on the magnification and the depth of the object being viewed.