"Zeroing" laser rangefinders

[Rodney65]

Sorry odd question but it comes up a lot for me. If your rangefinder's reticle and laser POI don't line up perfectly what's a good way to determine exactly where you need to hold on a target to get the best return?

I know some rangefinders make the reticle the same shape as the laser is supposed to be but I find they usually aren't perfect and some are pretty bad.

I saw some videos of digital night vision units with attached rangefinders and it was great because you could actually see the laser with infrared. Unfortunately I don't have anything like this.

Does anyone have system, something like using a solid tripod and ranging a telephone pole followed by a telephone wire, to determine exactly where the laser hits?

 

[B21TLB]

If you are using a 905 nm range finder you can see the beam with a Night Vision device. If its a 1550 you are pretty much out of luck unless you want to spend some serious money on a camera. You can use your Reticle (FFP works the best but SFP is accurate at a specific mag setting) and a telephone pole (they work well and are convenient to find) to get a good Idea of where your beam is. Start by ranging across the pole and noting on the reticle when you get a change in range. Go back the other way note the change in that direction on the reticle, you now have the width. Do the same using the top of the Pole for the top and bottom of the beam.

 

[spife7980]

I do something similar, I hang something on the barbed wire fence, and hold the button down so it’s a constant live ranging. when it reads 200 it’s the trees way behind, when I drift around and it reads 100 I know it’s picked up the object on the fence floating in relative space.
With my bushnell con-x I figured out I need to use the bottom point of the aiming circle trough, not the middle or top etc.
Green arrow points to my relative aiming location on this web pic.

 

[Rodney65]

Thanks for the replies. Those are basically the same techniques I use so I am glad I am not missing some secret technique like using a low light camera or something low tech like a special shaped target. I was also wondering if people had some trick to precisely map divergence like this somehow:

spife7980 that's also right abouts where my Sig Kilo 6K hits.

 

[Burdy]

Top of telephone pole against the skyline.

 

[CoryT]

Normally you can get the beam dimensions from the mfg. At 100 yards, take a sheet of cardboard and cut some holes to a bit over the beam size. For example, the Vector IV is 2 mil x 2mil, so cut a 7.5" square opening. if you center the reticle on that, you should range the target beyond it. If you get the cardboard, move the reticle around until you shoot through the hole. Now you know where the beam is in relation to the reticle.

 

[Rodney65]

Normally you can get the beam dimensions from the mfg. At 100 yards, take a sheet of cardboard and cut some holes to a bit over the beam size. For example, the Vector IV is 2 mil x 2mil, so cut a 7.5" square opening. if you center the reticle on that, you should range the target beyond it. If you get the cardboard, move the reticle around until you shoot through the hole. Now you know where the beam is in relation to the reticle.

The dimensions are 1.5x0.06 mil so it's a wide but very vertically thin beam I guess. Surprised it's smaller than anything by Vector as the 6K is much closer to entry level and a smaller beam seems more desirable.

I will try making a cutout slightly larger than 15x6mm and ranging at 100 meters, thanks for the suggestion. I can even mark the reticle hold point on the target after and have a great visual reference.

Is the beam divergence given in the specs usually pretty spot on?

 

[CoryT]

Divergence is normally a pretty tight spec, if it falls far outside then the unit will not perform as advertised.

Remember, the Vector IV is more than 20 years old, and it has a 1550nm laser. That uses MUCH more power than a typical 900nm commercial unit. You need about 50% of the beam on target to get a reliable range, unless the unit does multiple ranges, which the Vector does. The IV will get a good range on a 24" square target at 2000 meters. The 21 has a .7x.3 mil beam and will ping the same target at 4000.

Beam shape can be an issue, with a narrow but wide beam, your device is setup to range critters that are wide but not tall, like deer, elk and so forth. It would not be optimum for tall targets, like prairie dogs or people. You can of course change the device orientation to get the beam on the target, say you need to ping a telephone pole, turn the unit sideways so the vertical portion of the beam is oriented on the target axis and you get a range when held horizontal it misses.

really small beams SEEM like a good idea, right up until you find out the device is not perfectly collimated and the reticle is not where the beam is. Then it's a challenge to get the beam on the actual target, because of parallax error between the emitter and reticle plus lack of collimation.

As someone once said, it's complicated.

 

[Rodney65]

Divergence is normally a pretty tight spec, if it falls far outside then the unit will not perform as advertised.

Remember, the Vector IV is more than 20 years old, and it has a 1550nm laser. That uses MUCH more power than a typical 900nm commercial unit. You need about 50% of the beam on target to get a reliable range, unless the unit does multiple ranges, which the Vector does. The IV will get a good range on a 24" square target at 2000 meters. The 21 has a .7x.3 mil beam and will ping the same target at 4000.

Beam shape can be an issue, with a narrow but wide beam, your device is setup to range critters that are wide but not tall, like deer, elk and so forth. It would not be optimum for tall targets, like prairie dogs or people. You can of course change the device orientation to get the beam on the target, say you need to ping a telephone pole, turn the unit sideways so the vertical portion of the beam is oriented on the target axis and you get a range when held horizontal it misses.

really small beams SEEM like a good idea, right up until you find out the device is not perfectly collimated and the reticle is not where the beam is. Then it's a challenge to get the beam on the actual target, because of parallax error between the emitter and reticle plus lack of collimation.

As someone once said, it's complicated.

Thanks for the reply and input. 1.6 mil seems a bit wide to me as I am usually ranging coyotes, steel plates, or milk jugs. They're usually narrower than that, especially when the coyotes are square on to me but I guess that's how the rangefinder needs to be set up to work.