Athlon Optics Cronus ATS Pro 35CL-640 Clip-On Thermal

The Athlon Cronus ATS Pro 35CL-640 puts thermal imaging and a laser rangefinder in front of the riflescope you already shoot: Athlon designed it to ride the included QD Picatinny mount ahead of a low-power variable optic, or to clip onto the objective of a traditional hunting scope with an optional adapter. Inside its 17 oz housing is a 640 × 512, 12 μm sensor behind a 35 mm F1.0 lens, with a laser rangefinder rated to 1,600 yards and holdover data in MOA or MIL on screen. Guide's Orion O635CS has the same 640 × 512 sensor size and the same 12.5° × 9.4° field, is rated more sensitive (≤15 mK against ≤25 mK), weighs 10.05 oz, doubles as a handheld monocular and costs less; the 35CL-640 builds in the rangefinder and a ballistic calculator, and carries an IP68 rating to the Orion's IP67.

Key Features

• Laser ranging with holdover data. Single or continuous ranging (5, 10 or 20 seconds) measures from 10 to 1,600 yards to ±1 yard. With ballistic profiles built in the Athlon Ballistics app and uploaded to the clip-on, the calculator shows the holdover in MOA or MIL on screen in either mode. The smaller lens beside the battery cap, above the main objective, is the rangefinder's.

• Zeroed through your riflescope. For One Shot Zero you aim the riflescope's reticle at the target, fire, freeze the image and move the point of impact until it sits under the reticle's center. Zero at 50, 100, 200, 300 or 500 yards or meters; five profiles (A to E) save the zero distance, cartridge and rifle, and a leveling grid helps square the clip-on with the scope.
• 1x, so your riflescope sets the magnification. The 35CL-640 has 1X digital magnification (the 9.5X figure is the eyepiece magnification), so the magnification you see is your riflescope's. The menu can be scaled to 1X, 3X or 6X.
• Image tools. Hot track puts a white cross on the warmest point in view, and three scene modes (Natural, Enhanced, Highlight) work with seven color palettes and ten levels each of brightness and contrast.

• Auto-Shot recording with sound. Switched on, Auto-Shot records from 3 seconds before a shot to 7 seconds after, plus five images, with trigger sensitivity in five settings. With the microphone on, videos record sound, and 64 GB of built-in storage holds the files.
• One 18650 at a time. A single rechargeable 18650 battery runs the 35CL-640 for 5 hours or more. One comes in the box with a charging stand; the clip-on runs on the battery but does not charge it. With the battery flat, an external battery pack on the USB-C port can run it, and Eco mode fixes the screen at 20% brightness and switches off Wi-Fi and Auto-Shot.
• App and connections. Over Wi-Fi, the Athlon Thermal app changes settings, shows the live view and opens stored video and images. The USB-C port connects to a computer or an external screen.

• Sealed for weather. IP68, fog proof and shockproof, rated to work from -4°F to 122°F.

Who It's For

• Predator and varmint hunters who want to keep their daytime riflescope and add thermal and ranging in front of it. Its detection range is rated at 1,950 yards.
• Choosing among Athlon's clip-ons. The 35C-640 has the same sensor, lens, field and 1280 × 960 display without the laser (it uses stadiametric ranging instead), runs on two 18650 batteries for 9 hours or more and costs less. The 35CL-400 keeps the rangefinder with a 400 × 300 sensor, a narrower 7.8° × 5.9° field and 32 GB of storage, and costs less.
• Cross-shopping a rangefinder clip-on. Alpen's Apex 640 50mm Thermal Clip-On with LRF puts its 640 × 512 sensor behind a 50 mm lens, for a narrower 8.7° × 7° field and Alpen's 2,600 m detection rating, is rated ≤18 mK and runs up to 15 hours on two batteries. The 35CL-640's laser is rated farther (1,600 yards against 1,000 m), and it weighs 17 oz against 20.5, holds 64 GB to Alpen's 32 GB and costs less.

Accessories & Compatibility

• Scope adapters. For a traditional hunting scope, 40 mm, 50 mm and 56 mm thermal clip-on scope adapters are sold separately; each screws onto the clip-on and fastens to the objective of your day scope.