The limiting spatial resolution of an intensified imaging system depends on several factors, including (but not limited to)

  • Image intensifier type
  • Image intensifier gain
  • Pixel size

Before we can discuss each of these factors, we need to define what limiting spatial resolution means. When characterizing an imaging system, the limiting spatial resolution describes the smallest features that can be distinguished. There are several ways of characterizing the spatial resolotion, most of them use a test chart like the USAF resolution test chart. Such charts have a series of lines on them, the smaller the lines an imaging system can distinguish, the better the spatial resolution.

SilverFast Resolution Target USAF 1951 (Creative Commons 3.0)

SilverFast Resolution Target USAF 1951 (Creative Commons 3.0)

Spatial resolution is quantified in the number of line pairs that can be distinguised per millimeter (lp/mm). A line pair consists of a dark line and a bright line. So if one line is 5 microns wide, then a line pair will be 10 microns wide and there would be 1 mm/10 microns = 100 line pairs per millimeter.

Image intensifier type

There is a wide range of image intensifiers available. We advise our customers on the type of intensifier they need for their application based on the wavelengths that are important for our customers, and the frame rates they need. High-speed intensifiers usually have a lower spatial resolution than image intensifiers that are optimized for lower frame rates.

Image intensifier gain

We can increase the MCP voltage of an image intensifier to increase its gain. But MCP noise and the size of the electron cloud at the exit of the MCP also depend on the MCP voltage, so the spatial resolution will be slightly reduced as the MCP voltage is increased. You can learn more about how an image intensifier works on our image intensifier page.

Pixel size

Finally, the limiting spatial resolution of an imaging system is determined by the size of the pixels that collect the light from the image intensifier. You can use our intensifier-sensor matching calculator to find the theoretical maximum sensor resolution. It is calculated using the size of the pixels.

25 and 50 lp/mm (not to scale)

25 and 50 lp/mm (not to scale)

For example: If the pixels are 20 microns wide, we would need two adjacent pixels to distinguish a bright line and a dark line of a test chart. Those two pixels would have a total width of 40 microns, so the theoretical spatial resolution would be 1 mm/40 microns = 25 lp/mm.

The element of the imaging system with the lowest spatial resolution determines the limiting spatial resolution of the whole system. In our example, we have a sensor that has a limiting resolution of 25 lp/mm. If we have an image intensifier with a 50 lp/mm resolution, the size of the pixels would limit the resolution of the imaging system to 25 lp/mm.

However, if the pixels are smaller, 2 microns for instance, then the theoretical resolution of the sensor would be 250 lp/mm. In that case, the resolution of the image intensifier would determine the resolution of the total system.

Other factors

Many factors influence the spatial resolution of an intensified imaging system, like the size of the image intensifier, the number of image intensifiers and the optics. If you would like more information about the right image intensifier for your application, please contact us.

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