You’ve chosen your microscope and selected your camera.  Now you need to connect them correctly.  That’s where C-Mount adaptors come in.

What is a C-Mount adaptor?

A C-Mount adaptor is used to connect a camera – these days, usually a digital camera – to another optical device.  Although these adaptors were originally designed for use with 16mm movie cameras they have since become widely used for connecting cameras to CCTV equipment, machine vision systems and, yes, microscopes.

The derivation ‘C’ simply indicates that it is the third, after A and B, in a series of adaptors that evolved as movie camera and lens technology developed during the second half of the last century.

A C-Mount adaptor has a standard 25.5mm male thread, which mates to the thread on any microscope camera with a corresponding female thread; in practice, this is most cameras from leading manufacturers.  The other end of the adaptor either fits into the trinocular port of your microscope (the trinocular port is essentially a third lens port in a conventional binocular microscope), or replaces one of the eyepieces in microscopes without trinocular ports.

How does a C-Mount adaptor work?

The C-Mount adaptor can simply act as a connector between camera and microscope or can incorporate internal optics – often called reducer, relay or tube optics – to match the camera sensor size and compensate for differences between the different fields of view between the camera sensor and the microscope.

In each case, C-Mount adaptors are designed to match the magnification factor of the microscope eyepieces.  This allows the image shown on the camera to be as close as possible to that seen through the eyepieces, while optimising the area of the camera sensor that is used.  C-Mount adaptors also ensure that the camera remains perfectly focussed as the eyepieces are adjusted – this is termed ‘parfocal’. 

Note that if you do not need a camera image matched in size to that seen through the microscope eyepieces then a C-Mount adaptor without optics may be suitable.  For most users, however, matching the field of view of the two images is important, in which case a reducing C-Mount adaptor is normally required.  

It is worth noting that a microscope generally has a circular field of view, while camera sensors are rectangular or square, so inevitably there will always be something of a trade-off.  The common approach is to match the reducer lens to the diagonal dimension of the camera sensor.   

How to choose the correct C-Mount adaptor

With the wide range of microscopes from a variety of manufacturers being available it is important to choose the correct type and size of C-Mount adaptor, to ensure that it functions as expected and produces sharp images at all times.

If you have a microscope from one of the leading brands, such as Leica, Ziess, Nikon or Olympus, then there will normally be a dedicated adaptor available.  This will contain a reducer lens, be manufactured to work correctly with the specific model of microscope and available in several magnifications to give you the ability to match the specification of your camera sensor.

If you have a microscope from a supplier that does not offer dedicated C-Mount adaptors, or an older microscope from a leading brand that is no longer supported, then you will need to consider a generic adaptor from a specialised third-party manufacturer, such as Euromex.  Bear in mind that although there are various third-party suppliers, it is important to choose with care to ensure that that the trinocular port can be matched to generic adapters, as their diameters maybe incompatible. Reputable suppliers such as Euromex offer a wide range of C-Mount adaptors in a variety of magnifications, typically including objectives from 0.37x to 0.75x for 2/3” and 1/2” sensors, plus specialised adaptors for use with digital single lens reflex (DSLR) cameras with conventional APC-C sensors.

Which magnification do I need?

As a rule of thumb, to calculate the magnification, or objective size that you need for your C-Mount adaptor you need to know the sensor size of your camera and magnification of your microscope eyepieces.  With this information, working out the correct magnification is straightforward.

As an example, if your camera has a 1/2" sensor, simply divide the first integer by the second, i.e. one divided by two = 0.5.  If your eyepiece magnification is 10x, then you will need a 0.5x C-Mount adaptor.  A more powerful eyepiece magnification will require the next level of adaptor; for a 20x eyepiece you should therefore specify a 0.7x adaptor.  Bear in mind, that it is possible to use a stronger 0.7x adaptor with a 1/2" sensor and 10x eyepiece, but that this will produce a smaller field of view with greater magnification at the camera sensor than that seen through the microscope eyepieces.

Adding a camera to eyepiece tubes

As we have explained above, the most effective way to add a camera to your microscope is by using the trinocular port with a c-mount adapter.  Not all microscopes, however, have this type of port, and will therefore require a specialised adaptor that is designed to replace one of the binocular eyepieces.  Although less convenient, this setup can nonetheless produce acceptable results.

If in doubt: ask the experts

Although selecting the correct C-Mount adapter is relatively simple, there are as you’ll have read above a number of factors to consider.  If you have any doubts, or questions that are not answered in this post then please get in touch with our technical sales team.

Learn more on our blog with our suggested further reading:

Microscope Camera Guide