Laser Rangefinders: Function and Safety Explained

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Discussion Overview

The discussion focuses on the functionality and safety of laser rangefinders, particularly addressing how they operate with non-reflective surfaces and the potential eye hazards associated with their use. Participants explore theoretical and practical aspects of laser reflection, measurement techniques, and applications in surveying and optics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants question how laser rangefinders can function if the target object is not reflective, suggesting that absorption of laser light would prevent measurement.
  • Concerns are raised about the safety of laser light to the eyes, with references to external sources for safety information.
  • Participants discuss the effectiveness of concrete as a reflective surface for laser rangefinders, with some asserting that concrete does reflect light while others express skepticism about angles of incidence affecting measurement.
  • There is mention of using cube corner retro-reflectors to improve measurement accuracy, particularly in surveying contexts.
  • Some participants propose alternative methods for distance measurement, such as parallax-based rangefinders, while others express doubt about their availability and effectiveness.
  • Discussion includes the relationship between binocular magnification and depth of field, with participants seeking to understand the physics behind these concepts.

Areas of Agreement / Disagreement

Participants express a range of views on the effectiveness of laser rangefinders with different surfaces, the safety of laser use, and the relationship between binocular magnification and depth of field. There is no consensus on the best practices for using laser rangefinders in various conditions, and multiple competing perspectives remain throughout the discussion.

Contextual Notes

Participants reference external sources for information on laser rangefinders and safety, but there are limitations in the discussion regarding assumptions about surface reflectivity and the conditions under which laser rangefinders operate effectively. The discussion also touches on unresolved questions about the physics of light reflection and measurement techniques.

Who May Find This Useful

This discussion may be useful for individuals interested in laser rangefinders, surveying techniques, optics, and the physics of light, as well as those studying the relationship between optical magnification and depth of field.

cube137
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1. Laser rangefinder is said to work by the laser reflecting from the object and the device measuring the distance.. but if the object is not reflective.. how can the laser bounce back?

2. Is the laser in the Laser rangefinder harmful to the eyes?
 
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cube137 said:
1. Laser rangefinder is said to work by the laser reflecting from the object and the device measuring the distance.. but if the object is not reflective.. how can the laser bounce back?

2. Is the laser in the Laser rangefinder harmful to the eyes?
If the object absorbs too much of the laser light, then no, you will not be able to use a laser rangefinder for the job.

As to eye safety, that is covered in the wikipedia article: https://en.wikipedia.org/wiki/Laser_rangefinder

:smile:
 
berkeman said:
If the object absorbs too much of the laser light, then no, you will not be able to use a laser rangefinder for the job.

As to eye safety, that is covered in the wikipedia article: https://en.wikipedia.org/wiki/Laser_rangefinder

:smile:

how about concrete surface like in buildings.. how can it even reflect off concrete??
 
cube137 said:
how about concrete surface like in buildings.. how can it even reflect off concrete??
Use a window instead, or some other surface like metal that reflects well.

Also, did you read the wikipedia article? What do they suggest when the object is not very reflective? :smile:
 
berkeman said:
Use a window instead, or some other surface like metal that reflects well.

Also, did you read the wikipedia article? What do they suggest when the object is not very reflective? :smile:

I read it two times. It didn't suggest what to do if objective is not very reflective.. just black laser absorbing paint for military use.
Anyway. It's not written there what if the target surface is in an angle.. then the laser would bounce off an angle too.. but for the laser to bounce back to the device.. the surface has to be exactly 90 degrees to the line of site.. how often can you find such surface in the field??
 
cube137 said:
I read it two times. It didn't suggest what to do if objective is not very reflective.. just black laser absorbing paint for military use.
Anyway. It's not written there what if the target surface is in an angle.. then the laser would bounce off an angle too.. but for the laser to bounce back to the device.. the surface has to be exactly 90 degrees to the line of site.. how often can you find such surface in the field??
It said to use reflectors (like cube corner retro-reflectors). That's what surveyors use in their work with laser rangefinders. :smile:
 
berkeman said:
It said to use reflectors (like cube corner retro-reflectors). That's what surveyors use in their work with laser rangefinders. :smile:

I'll use it to measure the distances of buildings.. if the laser hits the concrete from an angle.. how can it reflect back to the device? Do you think it will work? Thanks :)
 
cube137 said:
how about concrete surface like in buildings.. how can it even reflect off concrete??
Laser light reflects off of concrete. If light didn't reflect off concrete, it would be black, not white!
 
russ_watters said:
Laser light reflects off of concrete. If light didn't reflect off concrete, it would be black, not white!

Makes sense. But if you hit it off at say 30 degrees from the sides, how can it return to the device, it should go on the other side.

I want to use it to estimate the distances of buildings because I'm studying the effect of binocular magnification and depth of field. How come lower magnification has larger depth of fields. For example. 7X binocular has objects in focus more than 25 yards? While 8X has shallow depth of field. What physics principles makes this happen? I want to use laser rangefinder to get the distances to the target.
 
  • #10
Most surfaces are not mirror like in their reflection property. For most surfaces the light is scattered in all directions and some gets back to the receiver.
 
  • #11
mathman said:
Most surfaces are not mirror like in their reflection property. For most surfaces the light is scattered in all directions and some gets back to the receiver.

What happens if the building is made of glass?
 
  • #12
cube137 said:
What happens if the building is made of glass?
Look, you need to go put cube corners on these buildings temporarily for your surveying of the distances for your project. Just have two people do the surveying. That is so standard... What is so hard to understand about this?
 
  • #13
berkeman said:
Look, you need to go put cube corners on these buildings temporarily for your surveying of the distances for your project. Just have two people do the surveying. That is so standard... What is so hard to understand about this?

https://www.amazon.com/dp/B00EF30VWA/?tag=pfamazon01-20

see above product.. it's supposed to be shoot and read... why.. does it only read for few selected targets only?
 
  • #14
cube137 said:
why.. does it only read for few selected targets only?
I didn't find that on a quick skim of the link but why do you think it says that?

Are you looking to use a laser rangefinder for an application? What is your application?
 
  • #15
berkeman said:
I didn't find that on a quick skim of the link but why do you think it says that?

Are you looking to use a laser rangefinder for an application? What is your application?

I have a binocular. I want to see the distance to any target...
 
  • #16
cube137 said:
I have a binocular. I want to see the distance to any target...
There are other ways to do this.

There are inexpensive rangefinders that use parallax to estimate the distance. Have you looked at those? Why do you need to estimate those distances?
 
  • #17
berkeman said:
There are other ways to do this.

There are inexpensive rangefinders that use parallax to estimate the distance. Have you looked at those? Why do you need to estimate those distances?

I understand to study the relationships between magnification of binocular and depth of fields.. lower magnification has greater depth of fields (meaning more objects in focus). I heard when you use 7X binocular.. everything beyond 25 yards is in focus.. but for higher magnification.. they are not in focus.. know the formula for determining magnification and depth of field? Thanks.
 
  • #18
cube137 said:
I understand to study the relationships between magnification of binocular and depth of fields.. lower magnification has greater depth of fields (meaning more objects in focus). I heard when you use 7X binocular.. everything beyond 25 yards is in focus.. but for higher magnification.. they are not in focus.. know the formula for determining magnification and depth of field? Thanks.
So for that you should be able to use a simple visual estimation of distance, IMO.
 
  • #19
cube137 said:
I heard when you use 7X binocular.. everything beyond 25 yards is in focus.. but for higher magnification.. they are not in focus..

that doesn't even begin to make sense

cube137 said:
know the formula for determining magnification and depth of field? Thanks.

read this wiki link on DOF

https://en.wikipedia.org/wiki/Depth_of_field
Dave
 
  • #20
mathman said:
Most surfaces are not mirror like in their reflection property. For most surfaces the light is scattered in all directions and some gets back to the receiver.
Which, again, is why you can see them!
 
  • #21
berkeman said:
There are inexpensive rangefinders that use parallax to estimate the distance. Have you looked at those?
I looked into this, a while ago, when I was with the National Coastwatch Institute (UK). There don't seem to be any parallax-based rangefinders available, except for some ancient WW2 models and that seem to be more like collectors' items.
I bought a cheap IR laser device that has a range, very dependent on the reflectivity of the target (max only a couple of hundred m). If you can't see a distant target then neither will the rangefinder.
 
  • #22
cube137 said:
1. Laser rangefinder is said to work by the laser reflecting from the object and the device measuring the distance.. but if the object is not reflective.. how can the laser bounce back?

2. Is the laser in the Laser rangefinder harmful to the eyes?
If you can see the object it is reflective.
 
  • #23
Buckleymanor said:
If you can see the object it is reflective.
But the converse is not necessarily true. "Stealth" construction, with highly reflective mirrors can give good specular reflections but in the wrong direction and you may see light, reflected from an object but due to light from other directions but the laser beam will not be reflected back to the rangefinder.
 
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