How Far Can the TNC4K219R See a Fox or a Pig?

Most buyers expect the thermal channel on the DNT ThermNight TNC4K219R to tell them what they're looking at. In practice it mostly tells you that something warm is out there. Going by the lens and sensor maths, the thermal picture picks up a fox out to roughly 275 m and a pig past 500 m, but it only shows enough shape to recognise a fox inside about 90 m and a pig inside about 180 m.

Past those distances, the 4K channel and the IR illuminator do the confirming, out to the IR's rated 450 yards (about 410 m). Use the scope that way and its range makes a lot of sense. DNT hasn't published a thermal detection range for this model, so every distance below comes from the optics themselves. The full spec sheet is in our DNT TNC4K219R review.

Why the thermal picture runs out first

Each thermal pixel looks at a fixed slice of the scene, and anything smaller than that slice blends into a single dot of colour. On the TNC4K219R, a 12 µm pixel behind the 19 mm lens covers about 0.63 milliradians. That's roughly 6.3 cm at 100 m, 12.6 cm at 200 m and 32 cm at 500 m.

The 4K camera spreads its 3840 pixels across an 8.8° view, so each one covers about 0.4 cm at 100 m. That makes the digital slice around 16 times finer than the thermal one at every distance. The diagram below puts the two side by side.

The slice size comes from pixel pitch and focal length, which is why the 19 mm lens matters as much as the 256×192 sensor. We go through that trade in whether a 256×192 sensor is enough for you. Contrast plays a part too: on a muggy night, when the animal and the grass sit close in temperature, a distant target fades sooner. There's more on that in how NETD affects the thermal picture.

The 2–8× thermal zoom enlarges those slices on the screen. It makes a distant dot easier to aim at, while the detail inside it stays the same.

How many pixels it takes to name the animal

Thermal makers size their range figures with the Johnson criteria, an old military rule of thumb. About 2 pixels across a target's smallest dimension (for an animal, its height) is enough to notice it. Six to 8 pixels lets you recognise what kind of animal it is, and around 12 lets you identify it with confidence.

These are probabilities rather than promises, and field experience counts for a lot when you're reading a few warm pixels. Still, they're the fairest way to turn a lens spec into distances. Here's what the thermal channel gives you, using an approximate fox height of 35 cm and a pig height of 70 cm.

The grids below show the same numbers as they'd land on the sensor. A fox at 300 m is a couple of warm cells, while a pig at 500 m still shows as a small block.

Foxes: the thermal finds, the 4K decides

Say you're scanning a dam bank at dusk and a warm spot appears on the far wall, around 220 m out. On thermal it's two or three pixels tall. That's enough to know something is sitting there, and too few to tell a fox from a feral cat or a hare.

Range it, switch to the 4K channel and bring the IR up. At 220 m each 4K sensor pixel covers under a centimetre, so ears, tail and the shape of the head come through, light permitting. That's the routine this scope is built around.

Inside about 70–90 m the thermal outline alone is usually enough to call a fox, and inside about 45 m it reaches the identify mark. Past 275 m or so, a fox drops below 2 pixels and is easy to sweep straight past, so slow the scan down on open ground.

Pigs on open ground

Picture a mob feeding across wheat stubble out on the western plains, 450 m away. Even at that distance each pig covers 2 to 3 pixels of height, so the mob shows up clearly as a cluster of warm blocks.

As you close in, the outline becomes recognisable at around 140 to 180 m. That's roughly where you can tell a pig from a roo or a calf on thermal alone. For picking out a big boar from the rest of the mob, or checking what's behind it, the 4K channel with IR does a better job anywhere inside its rated 410 m.

One caution on that IR figure: rated reach is a best case. Toward 400 m the 4K image gets dimmer and softer than the pixel maths suggests, and the real limit on any given night comes down to the illuminator, the moon and the background.

A routine that matches the optics

Put together, the two channels split the work by distance. The diagram below shows where each one takes over for a fox and a pig.

1. Scan on thermal at the low end of the zoom, where the view is widest.
2. Range anything warm with the laser, so you know whether it's inside the recognition line: about 90 m for a fox, 180 m for a pig.
3. Past that line, switch to the 4K channel with IR and confirm what it is before you take the shot.

Who it suits, and who should look elsewhere

For foxes and rabbits on your own place, and pigs inside a couple of hundred metres, we'd happily recommend the TNC4K219R. The find, range and confirm routine covers that work well, and the 4K channel gives you a far clearer look at the animal than a 256 thermal picture can.

Its weak spot is short thermal reach for recognition. The 19 mm lens keeps the view wide, and the trade is that animals turn into dots sooner than they would behind a longer lens.

If you mostly shoot pigs across big open country and want to call animals on thermal alone past 200 m, a longer thermal lens will suit you better. Its sibling, the TNC225R, uses a 25 mm thermal lens that stretches fox recognition to roughly 90–120 m by the same maths, though you give up the 4K camera. We weigh the two up in our TNC4K219R vs TNC225R comparison.

One more point if you often follow animals on the run. A buyer review on DNT's US store reported smearing and grain when tracking fast-running targets, clearing within about a second once the animal stopped. Walking animals didn't show it.

TNC4K219R viewing distance FAQ

Can the DNT TNC4K219R tell a fox from a cat at 100 m?

Not reliably on thermal alone. At 100 m a fox stands about 5 to 6 thermal pixels tall on the DNT TNC4K219R and a cat about 4, so both show as small warm shapes. Switch to the 4K channel with IR: each of its sensor pixels covers about 0.4 cm at that distance, which is plenty to show ears, tail and face shape.

How far can the DNT TNC4K219R see a deer?

By our calculation, the DNT TNC4K219R's thermal channel will detect a fallow-sized deer, about 90 cm at the shoulder, out to roughly 700 m. Recognising it as a deer on thermal needs you inside about 180 to 235 m. These are estimates from the 19 mm lens and 12 µm sensor using the Johnson criteria. For a positive ID, use the 4K channel with IR, rated to about 410 m.

How far can the DNT TNC4K219R see a rabbit?

A rabbit stands only about 20 cm tall, so the distances shrink. On the DNT TNC4K219R it covers 2 thermal pixels at around 160 m, enough to notice it. Recognising it as a rabbit on thermal needs you inside about 40 to 50 m. Beyond that, range it and confirm on the 4K channel with IR. These figures are our estimates from the lens and sensor specs.

What are the Johnson criteria for thermal scopes?

The Johnson criteria are a rule of thumb for how many pixels a target must cover before you can tell what it is. About 2 pixels across its smallest dimension lets you detect it, 6 to 8 lets you recognise the type of object, and around 12 lets you identify it. They describe probabilities, so weather, contrast and the shooter's experience all move the real result.

Does DNT publish a detection range for the TNC4K219R?

No. DNT lists the sensor, lens and field of view for the DNT TNC4K219R, but not a thermal detection distance. Some retailer listings quote 450 yards, which matches the IR illuminator's rated reach (about 410 m) for the 4K channel. Working from the lens and sensor specs, the thermal channel should detect a fox to roughly 275 m and a pig past 500 m.

Can I identify a pig at 300 m with the DNT TNC4K219R?

Yes, using the 4K channel. At 300 m a pig covers only about 4 pixels of height on the DNT TNC4K219R's thermal sensor, enough to see it but too few to sort one animal from another. The 4K channel with IR, rated to about 410 m, shows far finer detail at that range, though the image gets dimmer toward the edge of the IR's reach.

Do humid nights or fog shorten the TNC4K219R's viewing distance?

Yes. On muggy nights the ground, grass and animal sit closer in temperature, so a distant animal shows less contrast on the DNT TNC4K219R and needs to be closer before you notice it. Fog and heavy drizzle absorb and scatter infrared, cutting thermal range further, and they also scatter the IR illuminator's light for the 4K channel. Expect shorter distances than the calculated figures on those nights.

Can the 4K channel see past the IR range on a moonlit night?

To a degree. The DNT TNC4K219R's 4K camera uses whatever light is available, so a bright moon can let it show shapes beyond the IR illuminator's rated 450 yards (about 410 m). How far depends on moon phase, cloud cover and what's behind the animal. On a dark, overcast night the picture fades quickly past the IR's reach, so lean on the thermal to track and range.

Why does a fox look like a blob on thermal at 250 m?

At 250 m each thermal pixel on the DNT TNC4K219R covers about 16 cm, so a fox around 35 cm tall spans only 2 pixels or so. That's enough to show a warm spot, but too few for ears, tail or body shape. Zooming in enlarges the same pixels without adding detail. Range it, then switch to the 4K channel with IR to see what it is.

Related guides

• Our full DNT TNC4K219R review and spec sheet
• Whether a 256×192 thermal sensor is enough for your shooting
• How NETD affects thermal image quality on humid nights
• TNC4K219R vs TNC225R: where the extra money goes

Distances in this guide are our calculations from DNT's published sensor and lens specs using the Johnson criteria, so treat them as a guide that moves with weather, terrain and the animal.