How far you can see a person

112 m make out detail182 m tell what it is729 m spot it┆ maker’s claim

501002005001k2k5k m

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

Guide quotes 1,800 m, 2.5× our figure, because makers usually measure against a person’s full height rather than their width. Why the numbers differ

GuideClip-on · 640-class

Guide Orion O635CS

Name: Guide Orion O635CS
Brand: Guide
Price: 2099 USD

Price and availability on Guide’s site may differ.

Best for

Keeping your day scope and its zero while adding thermal at night

01Specifications

As published by Guide. Sources: guideir-thermal.com, guideoutdoor.com (single replaceable 18500 cell).

From the published specs, not owner reports.

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 (the best of 285 that publish it)
Swappable battery pack, so a spare doubles the run time
Light at 10.1 oz, the lightest of the 29 clip-ons here
Waterproof (IP67), survives a dunking
Warranty: 5 years (10 years on sensor)
~$2,099, well under the ~$3,499 typical for clip-ons here

Against it