Laser Rangefinders: Function and Safety Explained

[cube137]

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?

 

[berkeman]

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

 

[cube137]

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

how about concrete surface like in buildings.. how can it even reflect off concrete??

 

[berkeman]

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?

 

[cube137]

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?

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??

 

[berkeman]

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.

 

[cube137]

It said to use reflectors (like cube corner retro-reflectors). That's what surveyors use in their work with laser rangefinders.

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 :)

 

[russ_watters]

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!

 

[cube137]

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.

 

[mathman]

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.

 

[cube137]

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?

 

[berkeman]

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?

 

[cube137]

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?

 

[berkeman]

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?

 

[cube137]

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...

 

[berkeman]

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?

 

[cube137]

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.

 

[berkeman]

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.

 

[davenn]

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

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

 

[russ_watters]

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!

 

[sophiecentaur]

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.

 

[Buckleymanor]

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.

 

[sophiecentaur]

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.