What the specs mean

Detection range

The maker's figure for how far away a warm object shows up as a dot or two. It is far longer than the distance you can tell what the animal is.

Field width

How many feet of ground fill the screen at 100 yards. Wider makes scanning faster; narrower usually means more detail on the animal.

Identification distance

Our estimate of how far away you can tell a coyote from a fox or a dog. It is calculated from the lens and sensor, assuming good conditions.

Johnson's criteria

An old rule of thumb from imaging research: about 1.5 pixels to notice something, 6 to tell what kind of thing it is, and 12 to identify it.

Pixels on target

How many sensor pixels a coyote covers at a given distance. More pixels mean a clearer shape and a surer call on what you are looking at.

Color palettes

The color scheme the device uses to show heat, such as white-hot, black-hot or red. It changes how the picture looks, not what the sensor detects.

NETD (thermal sensitivity)

How small a temperature difference the sensor can show. Lower is better, but brands measure it differently, so numbers from two makers are not a fair comparison.

Pixel pitch

The size of each sensor pixel, in microns. Smaller pixels mean more magnification from the same lens. Most current thermals use 12 microns.

Refresh rate

How many times per second the picture updates. 50 or 60 times a second looks smooth; lower rates stutter when you pan or a coyote runs.

Sensor resolution

How many heat-reading pixels the sensor has, such as 384 × 288 or 640 × 512. More pixels show more detail, but the lens matters just as much.

Thermal imaging

A thermal device sees heat, not light. Every warm animal glows against cooler ground, day or night, with no light needed.

Base magnification

How much bigger things look before any digital zoom, like 2× or 4×. Higher is not automatically better: it narrows your view.

Digital zoom

Electronic enlarging of the picture. It makes the animal look bigger but adds no detail; past about 2× to 4× the image gets blocky.

Diopter adjustment

A focus ring on the eyepiece that sharpens the screen or tube image for your own eyesight. Set it once, then focus the front lens on the animal.

Display resolution

How many pixels the small screen inside the eyepiece has. A sharp screen looks cleaner but cannot add detail the sensor did not capture.

Eye relief

How far your eye sits behind the eyepiece and still sees the full picture. On a rifle scope, more distance keeps the scope off your face under recoil.

f-number

How much energy the lens lets in for its size, written like f/1.0. Smaller numbers gather more and help in poor conditions.

Field of view

How wide a view you get, in degrees. A wide view makes scanning for animals faster; a narrow one usually means more magnification.

Focal length

The lens number in millimeters, like 35 mm or 50 mm. A longer lens puts more pixels on a distant animal but shows a narrower slice of ground.

Objective lens

The front lens that gathers heat or light. Its size and material set much of a device's price, weight and reach.

850 nm vs 940 nm IR

The two common infrared light colors. 850 reaches farther with a cleaner picture but shows a faint red glow; 940 is close to invisible but reaches less far.

Autogating

A night vision tube feature that rapidly adjusts the tube's power when light gets bright, keeping the picture usable near headlights, yard lights or muzzle flash.

Cosmetic grade (tube blemishes)

How many small dark spots a night vision tube has in its picture, and where. Spots are cosmetic flaws, not a measure of how well the tube sees.

Digital night vision

A camera-style sensor that sees in very low light and in infrared, usually helped by a built-in infrared light. Cheaper than tubes, and it shows color by day.

Figure of merit (FOM)

A single number for night vision tube quality: resolution multiplied by signal-to-noise ratio. Higher is better, but check whether it is a guaranteed minimum.

Filmless and thin-filmed tubes

Gen 3 night vision tubes with their protective inner film removed or made thinner. Usually aimed at a cleaner picture in very low light.

Fusion

A device that combines thermal with night vision or a regular camera in one picture, so you see an animal's heat and the scene's detail together.

Green vs white phosphor

The color of the night vision picture. Green is traditional; white shows black and white. Many people find white more natural, but it is a preference.

Halo

A bright ring around lights seen through night vision, like a distant yard light. Smaller halos mean cleaner views near lights.

Image intensifier tube

The heart of traditional night vision. It takes the faint light from stars or moon and amplifies it thousands of times into a visible green or white picture.

IR illuminator

A flashlight of infrared light that people can barely see or not see at all. Digital night vision depends on it in the dark, and it often limits how far you can see.

ITAR (export control)

US rules that control the export of military-grade items, including most US-made Gen 3 night vision tubes. It limits who can own them and where they can go.

Manual gain

A knob that lets you turn night vision brightness up or down yourself, so you can keep contrast under a bright moon or near lights.

Signal-to-noise ratio (SNR)

How clean a night vision tube's picture is in very low light. Higher means less sparkle and grain on dark nights.

Tube data sheet

A test sheet for your specific night vision tube, listing its own measured figures. It shows exactly what you are getting instead of a range.

Tube generations

Labels like Gen 1, Gen 2+ and Gen 3 that group night vision tubes by design. They are a rough guide; the measured specs say more than the label.

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.

Ballistic calculator

Software in the scope that moves the aiming point for distance, using your bullet's data and the range to the animal.

Laser rangefinder

A built-in laser that measures how far away the animal is. The rated range is for big, reflective targets; expect much less on a coyote.

Zero profiles

Saved sight settings for different rifles or loads. Switch profiles instead of re-zeroing when you move the scope or change ammunition.

Battery life (runtime)

How many hours the device runs on a charge, by the maker's test. Real runtime is shorter in the cold and with Wi-Fi, recording or the rangefinder on.

Clip-on

A thermal or night vision unit that attaches in front of your day scope, so you keep your scope and its zero and add night viewing.

IP rating (water rating)

A two-part code for how well the device keeps out dust and water. IP67 means dust-tight and survives a short dunk; an X means not tested.

Mount

How the scope attaches to the rifle: standard rings or a rail clamp, fixed or quick-detach. A good mount does more to hold zero than anything else.

Onboard recording (storage)

Built-in memory that records photos and video of what you see. Useful for reviewing shots and sharing hunts; listed in gigabytes.

Operating temperature

The temperature range the maker says the device will work in. Batteries lose much of their runtime well before the low end of that range.

Recoil rating

How much rifle recoil the maker says the scope can take and still work and hold zero. Makers state it in different units, so compare carefully.

Weight

How heavy the device is. Check whether the maker weighed it with or without the battery, because brands do it differently.

Wi-Fi and app

A wireless link to a phone app for live viewing, downloading videos, changing settings and updating the device's software.

MSRP

The maker's suggested retail price in the US: the list price, before any sale. Useful for seeing how good a deal really is.

US price

The price we found for the unit in the US, with where it came from and when. Prices change often, so treat it as a snapshot.

Warranty

How long the maker promises to repair or replace a faulty unit. Check whether it needs registration and whether it passes to a second owner.