DNT Optics Hydra HS635 — 640×512 thermal riflescope

How far you can see a person

112 m make out detail182 m tell what it is729 m spot it

501002005001k2k5k m

Calculated from the sensor's pixel pitch and the lens focal length, for clear air.

DNT OpticsRiflescope · 640-class

DNT Optics Hydra HS635

Approx. price: ~$2,550
Sensor: 640×512 · 12 µm
Lens: 35 mm · 1.5×
Weight: 13.7 oz

We may earn a commission. Price and availability on Amazon’s site may differ.

Best for

A dedicated night rifle for hogs and coyotes inside about 150 yards

01Specifications

As published by DNT Optics. Sources: dntoptics.com.

Sensor: 640×512
Pixel pitch: 12 µm
NETD: ≤18 mK
Refresh rate: 50 Hz
Lens: 35 mm
Base magnification: 1.5×
Digital zoom: up to 6×
Display: 1024x768 OLED
Run time: 4 h
Battery type: 18650
Weight: 13.7 oz
Length: 7.9″
Laser rangefinder: No
Ballistic calculator: No
Wi-Fi: Yes
IP rating: IP67
Warranty: 2 years
Approx. price: ~$2,550

02Pros and cons

From the published specs. What owners report is in the next section.

For it

640×512 sensor, 3× the detail of an entry-level 384
Sensitive sensor that picks out small heat differences on humid or rainy nights (56th-best of 285 that publish it)
Takes 18650 batteries you can swap in the field
Light at 13.7 oz, 5th-lightest of the 194 riflescopes here
Waterproof (IP67), survives a dunking

Against it

Only 4 h of battery
Short 35 mm lens: a wide view, but less reach than a 50 mm scope
No rangefinder, so you judge distance by eye
Zoom past 1.5× is digital and gets blurry

03What owners say

owner discussions, 2025–2026

Summarised from 15 public owner discussions between 2025 and 2026. Owner experience, not a measurement.

Price is the whole story for most owners: a 640 sensor in a unit that works as a scope, a clip-on and a handheld for roughly $2,000 to $2,500. Owners who have moved up from a 384, or across from a first-generation AGM 640, call the screen a clear upgrade and the menus easy, and one hunter who runs a Pulsar as his main scope says the Hydra is impressive for half the money. An owner who has used both it and an iRay RH25 says the RH25 is only moderately cleaner and did not find more animals.

The clip-on mode is where opinions split. Some owners line it up easily in front of an LPVO and hit steel at 8x; others found it disappointing in front of a 2x prism or an ACOG, with a narrow field of view and an eye box that blurs unless everything is perfectly centred. The 1.5x base magnification is the other recurring regret, and several owners steer buyers who shoot past 150 yards toward the 50 mm Hydra instead.

What owners like

A 640 for around $2,000 to $2,500; an owner who also runs a first-generation AGM 35-640 says he would take the DNT 640 over an AGM 384 every time, given how much cheaper it is.
Owners coming from a 640 Rattler V1 or a 384 describe a noticeable screen upgrade and menus that are easy to learn.
Works as a standalone scope at ordinary hunting ranges: one owner identifies beaver- and turkey-sized game out to a couple of hundred yards, and another recorded bison at what he reckons was about 900 yards in Yellowstone.
In clip-on mode in front of an LPVO, one owner hit steel zoomed to 8x holding on the reticle, and another says it is easy to adjust and line up.
The app is smoother and easier to navigate than the one Nocpix and InfiRay use, according to an owner of both, and he has moved about a gigabyte of video off it without trouble.
Dealers and DNT itself get good marks for fast answers on mounting and setup questions, and owners mention a 30-day no-questions return window.

Common complaints

Clip-on performance in front of low-power prisms disappoints some owners: in front of a 2x prism and an ACOG one owner found the field of view badly cut down and the eye box blurring unless everything was perfectly centred.
The 1.5x base magnification is the most common regret; owners who shoot past about 150 yards suggest the higher-magnification 50 mm Hydra instead.
Finding a flip-to-side clip-on mount has been a hassle; owners report some magnifier mounts line up and others do not, and were waiting on a DNT-made solution.
A 2025 firmware update made clip-on mode look like 1x on one owner's unit even though the screen still read 1.5x.
The app's Wi-Fi link is weak, so live view lags or drops if the phone moves away from the scope, and one owner was waiting on a fix for the latest iOS.
Longevity is still an open question for owners who bought it on price: 'if this unit lasts' is a common caveat, and buyers note a shorter warranty than AGM's.

Hydra HS635 or an AGM Rattler 384 at the same price?

Most owners who have used both pick the Hydra for the 640 sensor, and one who runs a first-generation AGM 640 says he would choose the DNT 640 over an AGM 384 every time. The counterpoint from AGM owners is durability, customer service and a longer warranty, and that the Rattler's higher base magnification suits longer shots.

Does it work as a clip-on?

It depends on what is behind it. Owners running it in front of an LPVO say it lines up easily and they can hit steel zoomed in; one owner who tried it in front of a 2x prism and an ACOG found the view cramped and blurry off-centre and says it works much better as a standalone scope. Mounting it on a flip-to-side mount took experimenting.

The image was blurry when I turned it on. Is it defective?

Probably not. One owner who thought his new unit was faulty found the focus and diopter rings needed turning almost to the end of their travel before the image sharpened, and the dealer walked him through it.