Question about laser rangefinders

[DigTw0Grav3s]

Interesting. So how does a laser know not to fire at close range for eye-safe purposes?

[StainlessSteelCynic]

Originally Posted by DigTw0Grav3s

Interesting. So how does a laser know not to fire at close range for eye-safe purposes?

I don't actually know
Most manufacturers don't discuss the intricacies of their tech and a minimum safe distance limit was not something I ever encountered in some of the overlapping optical tech that I worked with
I have some ideas but they're educated guesses at best and "wild, shots in the dark" at worst
Note: LRF = Laser Range Finder

My first thought was that the focusing element might be set to disallow any action if the focal range is less than the minimum desired distance (with a lockout that prevents the laser from firing if the focal element is adjusted to equal/less than the minimum distance).
Keep in mind that the LRF is going to have some sort of integrated binocular or telescopic device so the operator can see the target (to allow them to line the LRF onto the target) so I'm thinking that at it's most basic, if the focus of the telescope is less than the minimum distance, then the LRF will not fire.

I suppose they could use a lower power beam to check target distance is greater than minimum safe distance before full power is applied but that just seems like "double-handling" and more complicated than necessary.
It's just as possible that they could fire a radio wave or IR beam first to check minimum distance before the main laser is engaged but again that seems like double-handling and extra complication (and just adds more stuff to break in the rangefinder!)
Personally I'm inclined to think they use the focusing system from the operator's optics.

[unkated]

I don't know but...

It is speed of light. Damage (to eyesight) is done over time - even if a short amount of time. If the response time is faster than the minimum range, it may be set to shutdown ASAP before calculating range (especially early models):

If time < .00002,
Then shutdown until new target
Else calculate range