Machine Vision Lens Selection: What to Consider

Choosing a lens for your vision system is a vital part of the process. The lens is at the front of any type of machine vision system – if the lens is not optimal for your application, results can be affected.

There are many factors that differentiate one lens from another, but there are a few major considerations you can take into account to choose the right lens.

3 Major Factors in Choosing the Best Lens

Researching lens qualities and other factors in your application will require some effort. Talking to a distributor is one of the best ways to ensure you choose the right lens.

Sensor and Application Measurements
Ideally, you’ll know the size of the sensor in your camera, the field of view and the distance from the object being monitored.

This information will reveal to you the focal length you require in your vision system. It will also tell you what size lens you need. Keep in mind the size of the lens needs to be greater than or equal to the size of the sensor.

Pixel Size in Lens Specifications
Lenses are rated by line parts per millimeter (lp/mm), not megapixels.  However, most manufacturers will only broadcast the megapixel value of a lens. This means that one 5 MP lens may not perform the same as another 5 MP lens.

Pixel size information may be difficult to obtain, due to the fact that it’s usually not advertised, but lens distributors have optical experts who can help you find a more accurate lens rating.

Lens Quality
The specific application dictates the quality of the lens needed. Here are some values to consider that will give you an idea of the lens quality you need:

• Modulation transfer function (MTF): a measurement of the intensity of light before it reaches the optics system compared to the intensity of light after it enters the optics system. Essentially, how well your lens transfers light.
• F#: the amount of light that can pass through the iris of a vision system, or, in other words, how much light can pass through the lens.
• Magnification: the number of times the image size is increased or decreased past its original size. You may need a special lens if you require large magnification or demagnification.

There are many important considerations to make when selecting the best lens for your application. Your entire vision system depends upon your lens, so choosing the correct one is important.

For expert guidance with machine vision lens selection, browse our lenses, where you will find industrial camera lenses from leading manufacturers.