The lens resolution in line pairs per mm (lp/mm) and camera pixel size both have an important role in digital imaging. The amount of line pairs per mm allow you to measure the spatial resolution of a camera or lens system. Pixel size refers to the physical size of a single pixel on an image camera sensor.

Please reach out to us if we can assist you in selecting a suitable lens for your industrial camera. 

What is the lens resolution?

The number of line pairs per mm refers to the amount of black and white lines distinguished per mm of image space. This is the lens resolution. The more line pairs per mm (lp/mm), the higher the spatial lens resolution is. This allows the industrial camera or lens system to resolve finer details in the image.

For example, a lens with a lens resolution of 100 lp/mm can resolve up to 100 pairs of black and white lines per mm of image space. The industrial camera can distinguish objects which are as close as 10 microns apart. This is a theoretical value, the actual physical performance will vary.

What is pixel size?

Pixel size is the physical size of a single pixel on an industrial camera's image sensor. The pixel size is measured in micro meters (μm). The total amount of pixels defines the resolution of a camera. For example, the MER2-160-227U3M camera has 1440x1080 = 1.555.200 pixels = 1.6MP resolution. A smaller pixel size means that you need a lens with a higher number of lp/mm.

Relationship between lens resolution and pixel size

The formula for calculating the relationship between the lens resolution and pixel size is as follows:

ξ  = (1lp/(2*s)) * (1000µm/1mm) 
with s = physical pixel size 

For example, our 9MP camera (ME2P-900-43U3M) with a pixel size of 2.5 microns will have a spatial lens resolution of 200 lp/mm.

Lp/mm lens overview

To find the lens resolution (lp/mm) matching the pixel size of your camera, consult the lens table. Fill in this form to receive access to our Download Page for the complete listing of all individual lenses we have in our portfolio with its lens resolution. 

Click on this link for a complete overview of our C-mount lens portfolio.
 

Lens series	Minimum Pixel Size	Center Pairs (lp/mm)	Edge Pairs (lp/mm)
1/1.8" 5MP	3.45μm	160	125
1/1.7" 12MP	1.85μm	250	160
2/3" 5MP	3.45μm	160	100
2/3" 10MP	2.4μm	250	160
1.1" 10MP	3.45μm	160	100
1.1" 20MP	2.75μm	200	125
1.1" 25MP	2.5μm	250	160
4/3" 20MP	2.5μm	200	125
1.1" 12MP Macro	3.45μm	160	100
1.4" 45MP	2μm	250	160

Lens resolution in the center vs. edge

The table above shows the difference between the number of line pairs per mm (lp/mm) in the center and edges of the lens. This lens resolution also translates to the image taken by the industrial camera, the image is slightly sharper in the center than what it is in the corners. In general, when calculating the correct lens for the pixel size of the camera, the lp/mm of the center is used. 

Recommendations to match a lens with an industrial camera

Use the lens table above as a reference for matching the lens resolution, the number of lp/mm, with the pixel size of your industrial camera. In some cases, a lens with a relatively low number of lp/mm than required is acceptable for your industrial camera sensor pixel size:
-    When you have a limited budget to buy a lens with a higher lens resolution (more lp/mm)
-    A very light sensitive lens with f1.8 aperture or lower is required, which is not available in a higher resolution (higher lp/mm) lens

In some circumstances a lens with lower resolution may cause a slightly less sharper image however depending on your application, it may be acceptable. Please contact us if we can still advise you on calculating the lens resolution.