For ID distances, here is an example of my calcuations, compare a good Dahua starlight camera to the Arlos/Ring/Nest and other products
Dahua IPC-HDW4231EM-AS starlight fixed lens 1080p 1920x1080
w/2.8mm lens FOV H 110 degrees: 10 feet { area covered 95.94 sq feet covered }
w/3.6mm lens FOV H 87 degrees: 12.65 feet { 121.43 sq feet covered }
w/6mm lens FOV H 51 degrees: 21.58 feet { 207.16 sq feet covered }
ID spec distance and associated area max covered calculations ( 100ppf+ ):
This is the theoretical max based on raw pixels from the horizontal resolution and the horizontal FOV. Calculations based on data provided in ads / spec sheets. Some vendors like to play games and list diagonal FOV instead of horizontal FOV as that number is bigger and not clarify that it is diagonal FOV.
Actual real world results will be decreased due to the quality of the camera ( glass vs plastic lens, compression quality, sw/firmware,... ), installation view, as well as environmental conditions ( low light, haze, fog, glare off snow, water rain,.. ).
Practical meaning: Place your cameras in such a manner that any suspect / subject you wish to potentially ID is within this ID spec distance, as well as in a placement which will give you a high likelihood of obtaining a good facial image ( mount camera 8 feet or less high ).
compare to:
Ring Video
Doorbell 720p at 160 degrees: 4.08 feet { 23.23 sq feet covered }
Logitech Logi Circle HD Wireless Security Camera 720p at 135 degrees: 5.44 feet { 34.85 sq feet covered }
Arlo Pro / Arlo Go 720p at 130 degress: 5.644 feet { 36.12 sq feet covered }
Logitech Circle 2 (V-R0008) 1080p at 180 degrees: 6.11 feet { 58.6 sq feet covered }
ezviz Mini Trooper 720p wire free cam at 116° : 6.33 feet { 40.54 sq feet covered }
Foscam C1 720p at 115 degrees: 6.38 feet { 40 sq feet covered }
YI Home Camera 720p at 111 degrees: 6.61 feet { 42.3 sq feet covered }
Arlo 720p at 110 degrees: 6.67 feet { 42.68 sq feet covered }
Blink XT - 720p ( 1080p version is planned ) at 110 degrees: 6.67 feet { 42.68 sq feet covered }
Ring Video Doorbell 2 / Pro / Elite 1080p at 160 degrees: 6.88 feet { 66.06 sq feet covered }
Ring Spotlight Cam wired / battery / solar 1080p at 140 degrees: 7.86 feet { 75.44 sq feet covered }
Ring Floodlight Cam 1080p at 140 degrees: 7.86 feet { 75.44 sq feet covered }
D-Link DCS-933L 640x480 at 45.3: 8.0988 feet { 25.92 sq feet covered }
ezviz CV-200 Mini Plus 1080p 135° : 8.15 feet { 78.21 sq feet covered }
Arlo Q / Arlo Q plus 1080p at 130 degrees: 8.47 feet { 81.34 sq feet covered }
Arlo Pro 2 1080p at 130 degrees: 8.47 feet { 81.34 sq feet covered }
Nest Cam Outdoor / Indoor 1080p at 130 degrees: 8.47 feet { 81.34 sq feet covered }
Samsung SmartCam SNH-V6431BN / V6414BN 1080p at 130 degrees: 8.47 feet { 81.34 sq feet covered }
Xiaomi MIJIA Smart 1080P IP Camera at 130 degrees: 8.47 feet { 81.34 sq feet covered }
Amcrest IPM-721S 720p IP camera at 85 deg H FOV as per chat w/Amcrest: 8.63 feet { 55.2 sq feet covered }
Zmodo
"spoe is not compatible with poe" bullet cam 2.8mm 720p at 81 degrees: 9.06 feet {57.99 sq feet covered }
Ring Stick Up 720p at 80 degrees: 9.17 feet { 58.67 sq feet covered }
Canary Flex 1080p at 116 degrees: 9.488 feet { 91.08 sq feet covered }
YI Dome Camera 1080p HD 112°: 9.82 feet { 94.396 sq feet covered }
Foscam R2 1080p at 110 degrees: 10.00 feet { 95.94 sq feet covered }
Reolink Argus 1080p at 130 110°: 8.47 10.00 feet { 81.34 95.94 sq feet covered }
Amcrest ProHD 1080p IP2M-841 / IP2M-841B at 90 degrees: 12.23 feet { 117.41 sq feet covered }
Annke AU-I61DR0104#US1 Cube Camera 4mm 1080p at 85°: 12.95 feet { 124.33 sq feet covered }
Swann PRO-T852 BNC connectors 1080p 80°: 13.76 feet { 132.12 sq feet covered }