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FAQ: I am unable to obtain equally focused images through the camera and eyepiece. There are a few millimetres between the two focal planes!

If the focal planes of the specimen differ widely (> 10 mm) between the camera display (through the phototube) and visual observation via the eyepiece, your instrument has a C-mount connection that differs from the general standards. Dental and operating microscopes in particular sometimes have C-mount connections that are incompatible with standard C-mount connections.



The above illustration shows a setup in which the two optical paths (eyepiece and phototube) are aligned differently. If the image through the eyepiece is focused, the image that the camera sees (through the phototube) is blurred. By turning the micrometer screw it is possible to ensure that the camera also sees a focused image. This process is known as defocusing. It changes the distance (h) between the object and the eyepiece. This difference should be corrected for reasons of optical quality.


The C-mount connection is a standardised connection that has been designed for video cameras. Using this connection makes it possible to attach cameras made by different manufacturers to phototubes. The thread is imperial (inches) and has an external diameter of 25.4 mm. The distance from the camera’s sensor chip is known as the flange focal distance (or flange-to-film distance) and is set at 17.52 mm.  

Possible solution:

We have developed a focusable LM Universal Adapter, which compensates the deviation of the instrument. For extreme differences you have the possibility to use a 5mm C-Mount extension.

Update: 04.04.2011