Choosing a CMOS Image Sensor is the easy bit. Once you have chosen your sensor a suitable lens and lens assembly needs to be found. A PCB mount lens holder will screw to the PCB, covering up your sensor from light. The top of the holder will have a standard thread which will allow you to screw in a lens with the same thread type. The lens holder may also incorporate a Infra-Red Cut Off filter and is typically made of Black ABS Plastic or Black Anodised Diecast Aluminium.

The typical thread sizes are detailed below,

The aperture number, f Number or f / # specifies the amount of light which passes through the lens. The lower the number, the more light that will pass through the lens, thus the better performance in low light conditions. Every time the f number doubles, the light is reduced by a factor of 4. A lower f-number requires more precise adjustment of focus, where as a lens with a high f-number will be easier to focus. Eyeball cameras for PC imaging have a typical f-number of 1.8 to 2.0 where 2.0 is standard for most S-Mount Lenses. Pinhole lens, while having the ability to be concealed behind a hole have a high f-number thus are not as effective in low light environments.

The pixel element of a CMOS sensor is normally susceptible to a greater span of the electromagnetic spectrum than the human eye. The sensors ability will range from the deep blues to almost infra-red. To get a more accurate measure of what the human eye is seeing, an IR Cut Off filter is included with most lens mounts or lenses. Colour aliasing and blurring can be a consequence of omitting the IR Cut Filter on a colour imaging system.

As the IR cut off filter can either be part of the lens or lens assembly this will need to check on purchasing. The filter present on a lens mount looks like a bit of thick glass mounted to the bottom of the mount. This is normally made up of several layers of optical crystal with a IR Cut Crystal layer. Beware of some lens having a film on the back of the lens as these are easy to scratch.