Laser rangefinder viewed through an IR digital camera

[Alaskan]

Months ago I asked if anyone here had a small 905 nm laser rangefinder they could try to record the IR pulse laser output from using a cell phone, no one had a rangefinder to try with. After returning from working in Iraq, I finally purchased a used rangefinder and tried to do so using my iPhone, but found the infrared output to be extremely weak due to the cameras internal IR filter which would not allow much of the invisible light to pass through to the camera sensor.

 

[Radim]

Not sure about your LPM spectral range, but it works like this for human eye:


Source: Wiki - more under click.

For LPM there will be some curve like this. For IR camera another. You might somehow estimate it with gaussian (if you know spectral specs of your LPM). It seems to me 1.5 mW is just the tail of the distribution.

Just be careful not to damage your camera's sensor with enormous focussed laser power. Some pixels might die (really this is laserpainter's nightmare).

 

[Radim]

That seems legit to me. Maybe the range finder adjusts power and/or focus according to distance of scene illuminated? Something like advanced laser dazzlers do - adjusting the output not to exceed MPE and be still effective in dazzling effect.

BTW I just realized I might need that LPM.

 

[paul1598419]

I bought an IR VIS CMOS video camera 4 or 5 years ago just to focus my IR builds. Mine has a green tint to it, but is also monochrome in IR mode. I don't think that haystack graph pertains to any LPMs. It sure doesn't for the four that I have. I have seen the Coherent LaserCheck LPM for sale many time on eBay and they are pretty good for very low power lasers. Have you made a video of a CW IR laser with your camera, Chris? I was wondering if it could take beam shots.

 

[Radim]

I suppose a rangefinder could do that, but I don't believe this el chepo rangefinder does that. I pad two dollars for this one used off of ebay, the battery for it cost me more than that. New, they are much more, of course. This little LPM can only measure up to 1 watt, if you slide the little attenuator in front of the sensor. My wife was having a difficult time targeting me, that's why much of the time it the IR wasn't directly on me.

Might do. Even a cheap electronics is complex now. Depends on overall performance. Use it under various conditions to find out. Also variable ISO of the camera might play role and the mechanism might be right there (narrow spectre of the sensor relates to less noise at high ISOs IMO).

Regarding that LPM I'm thinking more about precision illumination measurement at some certain spots. Mostly diffused and reflected light. Not measuring laser output directly. Since I mentioned in some LPF post recently - I'm planning laserpainting of public areas and here precise device to measure laser illumination is needed to be safe.

The LPF post indicating my laserpainting projects related (link).

 

[Radim]

My name is Radim. You know it already.

I think in case of diode they mean PWM by variable pulse.

Nice video. I would try to make it still on tripod and move slightly across the objects with various albedos to see if in case of brighter dot detected the power is reduced.

 

[Radim]

Yeah, but we all know how is it with cheap lasers and power ratings. I would search for certification of that product if any. Some kind of compliance.

Edit:

For context:

Click on pic for more.

This is another kind of rangefinder. Definitely class 4.

 

[lasersbee]

Here are the specs on the Coherent LaserCheck LPM - the wavelength specs are fairly flat from 400 through 1064 nm at 8% accuracy, at least, when newly calibrated. Thermopile laser power meters are far flatter in their response than cameras, so those curves are not applicable to this LPM. Cameras are built with that kind of response to wavelength to mimic the what the eye sees, this type of LPM is made to measure heat across a fairly flat spectrum of wavelengths, within limits of course, as below.

Chris... The LaserCheck uses an optical sensor
and detects photons.. not heat...

Interesting experiment...

Jerry

 

[paul1598419]

I have seen this before on consumer IR rangefinders. It must be written into law that their power no exceed 1 mW. Makes sense if you think about it, though.

 

[lasersbee]

Yes, it later occurred to me it uses a photonic sensor, not a thermopile. I had wrongly responded as if it used a thermopile like my other laser power meters, I was going to edit that in, but so many posts responding to it already, that and the sensor on the LaserCheck was also fairly flat to 400-1064 nm, similar to a thermopile LPM, I decided to leave it alone but I keep finding time to come back to the thread today anyway, as I'm getting ready to go to Qatar. Updated the post.

One of my concerns was whether the synch of CCD video camera might miss the narrow nanosecond IR laser diode pulses, it sure didn't, appears the rangefinder puts out a continuous uninterrupted train of pulses, you can't miss it. I am very pleased with finding this as I'd like to mount the little IR board in a pointer to have a pulsed 905 nm source.

The LaserCheck LPM is Firmware corrected to
the Wavelength that you are using... But you
need to tell the LaserCheck what wavelength
you are using BEFORE you take a reading.

If you don't set the LaserCheck to the
wavelength of the Laser you are testing
the Readings will be much further off than
8%...

The Optical Power Curve of the sensor is
not linear at all...


Jerry

 

[paul1598419]

That is true of all LPMs that use an optical sensor.

 

[lasersbee]

FYI... That's not a double Post. Double Posts happen
within less than an ~hour interval..

Have you tried to put the rangefinder/camera on a
tripod to reduce the shaking ??


Jerry

 

[Radim]

FYI... That's not a double Post. Double Posts happen
within less than an ~hour interval..

Have you tried to put the rangefinder/camera on a
tripod to reduce the shaking ??


Jerry

This ^^^^^

BTW: I still think the sensor had to suffer when getting direct hits (even of low power).

 

[lasersbee]

It would depend on the sensor's specs...
1mW from a distance is not that much for an optical sensor.

Jerry

 

[Radim]

Not too much, but seeing these flashes, the pixels in the center of the flashes might get enough stress to reduce their lifetime IMO. Even low powered laser can do some harm under certain conditions. Depends on collimation as well. For example beam "focussed to infinity" and camera as well to infinity (like 15+ m) is deadly combination in near field... Hopefully it is not costly and for that purpose bought camera.

 

[Radim]

If this is a class 1 laser and under .39 milliwatts output, as wide as that beam is, I'm not concerned there will be damage to a pixel, the power density per pixel has got to be very small. Accidentally crossing the sun would be a huge amount more and this camera is for day or night use.

0.39 mW max - that should be ok than. But you know some cameras might be damaged by direct sunlight hit.

Can I damage my camera by pointing it at the sun? :: Digital Photo Secrets

I just missed somehow 0.39 mW. And in case of night vision cameras I woulud not be surprised they have lower treshold than normal cameras.

You know - I'm always scared when taking pics with lasers. But my mobile cam sustained direct hit from WL Evo at full over 100 mW from like 40 - 50 meters without any visible damage. Still I did not went pixel by pixel as I do with my digital cameras. I even took a pic closer as low as about 30 meters once. No problems.

Edit to your Edit:
You do not need tripod. Just put camera on something like chair with piece of cloth to be folded and adjusted for right view. I often use what I find in the forest as tripod.

Edit 2: When I look back most of my recent artworks were taken with camera without tripod. I had two large, one is broken and second was used for laser if used. Due to being creative and lacking tripods I often need just natural material like branches, leaves, stones and some artificial like duct tape, rope, black paper, plastic bags, cloth... Anything to fix things and make lasers in operating conditions.