Tube resolution (lp/mm)
How fine a detail a night vision tube can show, in line pairs per millimeter. Higher is sharper, but it is measured in a lab in good light.
What it means
Tube resolution is measured by looking at a test pattern of alternating dark and light bars through the tube. The finest pattern you can still see as separate lines sets the figure, in line pairs per millimeter (lp/mm): one dark bar plus one light bar is one line pair, and the millimeter is measured on the tube’s light-catching surface. Current tubes commonly list about 57 to 72 lp/mm; some sellers give a range, such as 64 to 72.
What it changes in the field
Higher resolution means sharper edges and finer detail: an animal’s ears, a fence wire, the outline of a hog against brush. But the figure is a lab limit measured with plenty of light. On a dark night, noise in the tube blurs fine detail long before you reach that limit, which is why signal-to-noise ratio matters more on the darkest nights. The housing’s lens also lowers the sharpness of the whole system.
From lp/mm to the animal
Resolution on the tube becomes detail in the field through the front lens. Multiply lp/mm by the lens focal length in millimeters and divide by 1,000 to get line pairs per milliradian of view. A 64 lp/mm tube behind a 26 mm lens, common on monoculars, gives about 1.7 line pairs per milliradian. A longer lens or a magnifier multiplies it, at the cost of a narrower view.
What to look for
- Whether the figure is a minimum, a range or a typical value.
- Resolution together with FOM and signal-to-noise ratio, not alone.
- The housing’s lens: a fast, sharp lens lets the tube’s resolution show.
How we use it on this site
We record the maker’s figure as published. When we turn it into angular resolution, we use the bottom of the published range and label it a lab limit in bright light.