To use a camera with a microscope, it is necessary to match the diameter of the real image produced by the microscope that would be viewed directly through an eyepiece. Depending on the type of objective and other design factors, this diameter can be in the range covering less than 10 to more than 25 mm. However, in most microscopes, the diameter is in the range of 17 to 22 mm.
Compare this to the size of a typical image sensor. In digital still cameras, the image sensor is often large enough that the entire microscope image diameter can be viewed. For example, if the microscope images in 20 mm and a camera with a full-size 35 mm equivalent sensor is used, the image sensor is 24 x 36 mm. This means that the camera image will show the entire microscope circle with a large area of unused sensor if the camera is simply mounted at the microscope output.
To utilize more of a large image sensor, an optical adapter (or coupler) is used that includes a lens to change the size of the image. The ratio of the diameter of the output image to the diameter of the input image is called magnification. The user must select a coupler with the correct magnification to produce the image presentation desired. For instance, if the image diameter is to be fitted to the height of the sensor, then in this case, the magnification woudl be 24/20 = 1.2x. If the image is to be fitted to the width of the sensor, then the magnification would be 36/20 = 1.8x. If the image is to be fitted to the diagonal of the sensor so that the whole sensor is used, then the magnification woudl be 43.3/20 = 2.2x (approximately)
In video cameras, the sensors are usually smaller than the microscope image diameter. For instance, a 1/3" sensor is about 3.6 x 4.8 mm (6mm diagonal). If the microscope image diameter is 20 mm, then the required magnification for all cases will be less than 1. Without an adapter, the camera will only see a small part of the center of the image. For the three cases, the required magnifications are: Match height - 3.6/20 = 0.18x; Match width - 4.8/20 = 0.24x; Match diagonal - 6/20 = 0.3x.
Here is another example with a 2/3" sensor:
Here, the image diameter is 20 mm and the sensor has an 11 mm image diagonal (8.8 x 6.6 mm active area). With a 1x adapter, only a small portion of the center of the microscope image will be displayed on the monitor. A 0.5x adapter approximately matches the sensor diagonal to the image diameter and a 0.3x adapter allows the whole microscope image to be viewed.
Similar calculations can be used for any other combinations of microscope image diameter and sensor size to specify the magnification required for the desired effect. However, since adapters are generally available in only a few magnifications, it may be necessary to select one above or below the ideal value. Only the user can decide which side of optimum is more useful.
Our selection of Microscope Adapters may be viewed here.