Machine Vision Lens Calculator

Lens choice comes down to three numbers: the sensor size, the working distance and the field of view you need. Together they fix the focal length, which is roughly the sensor size times the working distance divided by the field of view. The lens then has to do two more things, cover the whole sensor without dark corners and resolve enough detail for the camera's pixels. This calculator works all of that out and shortlists a matching lens from our range.

Sensor format is the optical size of the sensor, quoted in inches such as 2/3 inch or 1.1 inch, or as a diagonal in millimetres. It matters because every lens projects an image circle of a fixed size, and that image circle must be equal to or larger than the sensor, or the corners of the image fall dark, which is called vignetting. One catch worth knowing is that the same inch label can mean slightly different millimetre sizes between sensor makers, so the real width and height in millimetres is what counts, which is why this tool derives them from your resolution and pixel size.

Focal length sets the angle of view. A shorter focal length gives a wider view and lets the object sit closer, while a longer focal length gives a narrower view with more magnification and suits objects further away. As a guide, the focal length is about the sensor size multiplied by the working distance and divided by the field of view. Enter your working distance and the size of the object and the calculator returns the focal length, then matches it to the nearest lenses we stock.

A lens has its own resolving power, often quoted as a megapixel rating or a supported pixel size in microns. The lens has to resolve detail down to the size of the camera's pixels, so a lens rated for a low resolution will bottleneck a high resolution sensor no matter how good the camera is. As a rule the lens rating should meet or exceed the sensor, and modern sensors with pixels around 2.74 to 3.45 microns need lenses designed for that level.

The F-number sets how much light the lens lets in and how much depth of field you get. A wider aperture, meaning a smaller F-number, gathers more light and suits fast lines and short exposures, but gives a shallower depth of field. A smaller aperture, meaning a larger F-number, deepens the focus range but eventually softens the image through diffraction. The calculator shows this trade and warns you when the aperture is stopped down too far for your pixels.

Closing the aperture down increases depth of field, but past a point the diffraction blur, called the Airy disc, grows larger than a pixel and fine detail is lost. There is therefore a maximum recommended F-number for any sensor and lens combination. The calculator computes it for your setup and flags when your chosen aperture goes beyond it, so you can open up or accept the trade for more depth of field.

Depth of field is the range of distance, in front of and behind the focus point, that stays acceptably sharp. You get more of it by using a smaller aperture or a shorter focal length, and less of it up close at high magnification. It is always a balance, because a smaller aperture costs light and eventually brings in diffraction, which is why it helps to see all three together as the calculator shows.

The mount has to match between the lens and the camera. C-mount is the most common in machine vision, with a flange distance of 17.526mm, and it covers sensors up to around 1.1 inch. CS-mount sits closer to the sensor at 12.5mm and is found on compact cameras. Larger sensors move to F-mount, TFL-mount or M42, which project a bigger image circle. The safest check is your camera's mount and the sensor format together.

Telecentric lenses hold magnification constant regardless of where the object sits within their range, which removes the perspective error that ordinary lenses introduce. That makes them the right choice for accurate measurement and gauging, where a feature must read the same size wherever it falls in the field. For inspection where you are checking presence, defects or codes rather than precise dimensions, a standard fixed focal length lens is usually the better value.

A fixed focal length lens is set to one focal length and holds it, which gives the most stable and repeatable result on a production line, so it is the usual choice for machine vision. Varifocal and zoom lenses let you adjust the focal length, which helps during setup or where one camera has to cover several product sizes, at some cost to repeatability. For a fixed station the fixed lens is normally preferred.

Yes. Most machine vision lenses are corrected for visible light and the near infrared, but they do not all behave the same across wavelengths, and focus can shift between visible and infrared. Shortwave infrared, or SWIR, needs lenses specifically corrected for that band, which is why the calculator filters the shortlist by the spectral band you select. If you are imaging outside normal visible light, tell us the waveband and we will confirm the optics.