To understand more about why we needed to develop our giant lens, it is necessary to explain how a confocal microscope works.

A confocal microscope records from only one tiny spot in the specimen at any one time, and builds up an image over time by scanning the spot over the specimen. Light from a laser is passed down into the microscope via a pair of scanning mirrors which can be turned to produce horizontal or vertical movement of the spot. The laser light goes through the microscope and is focussed as sharply as possible within the specimen . If this produces some light emission (e.g. because the specimen is shiny or fluorescent), the emitted light goes back up through the microscope. In the short time it takes to do this, the scanning mirrors have not moved appreciably, so the emitted light is returned along the path by which the laser light entered. The emitted light would, in fact, go back into the laser, but the reflector is a special one, allowing only the emitted light to pass through towards the detector of light. A key feature is the addition of a pinhole, into which the emitted light is focussed on its way to the detector.

The word ‘confocal’ refers to the fact that the spot in the specimen is focussed onto the pinhole.