A key criterion for choosing the right camera is the amount of light at the microscope. The less light available, the greater the light sensitivity of the camera needs to be. Generally speaking, a pixel size of 6.45 µm or larger offers excellent light sensitivity for crystal-clear, low-noise images. However, this comes at a trade-off because the larger the physical pixel size, the less pixels can be fit on the sensor, reducing resolution.
The sensor sizes determine the real-estate in which pixels are placed in an array. Most scientific-grade cameras incorporate large sensors, for example, 2/3” – 1”, because pixel size and pixel quantity are both maximized. However, cameras used for documenting conventional bright-field images may use an image sensor smaller than 1/2” due to their inherent smaller pixel sizes and smaller quantity of pixels. Regardless, the correct magnification c-mount adapter must be chosen based on the sensor size to avoid vignetting or compromised field-of-view.
Driven by the mega-pixel hungry consumer market, which users know from photography, digital resolution, or quantity of pixels, is easily misperceived as image quality. Truth is, micro-imaging applications require less pixels than macro-imaging. If you work mostly at very high magnifications, the optical system is limited to about 3–5 megapixels that can be transferred to the sensor of a camera. Setting the camera to a high resolution of, say, 12 megapixels would produce a larger image, but you would not gain any additional information. If you use the microscope at low magnification on the other hand, then you definitely need a high resolution digital camera to capture all the details that your microscope can deliver. To learn more about the relation between resolution and image quality with microscope cameras read the short explanation on Leica Science Lab. http://www.leica-microsystems.com/science-lab/digital-cameras/
CCD vs. CMOS