Rifle Scopes Optical rangefinder: Why not?

[rg1911]

Since I need a replacement rangefinder, I've been reading all the posts I can find. It sounds as though even the big name, high dollar rangefinders can become tempermental or just plain inoperative. And all are adversely affected by rain, bright sun, non-reflective targets, targets low to the ground, etc.

So my question is: Is there a purely optical rangefinder available? And if not, why not?

I have one of the large, old Swiss artillery rangefinders, but it's not what I'd call portable. And I don't often need to range out to 20-thousand meters.

But it isn't bothered by any of the things that affect laser rangefinders and it doesn't have electronics that will self-destruct in a few years.

I don't understand why one of the optics companies doesn't make a small optical rangefinder that works out to, say, 2000 yards.

What am I missing here?

Thank you,
Richard

 

[Kiba]

Re: Optical rangefinder: Why not?

There are/were a couple of small handheld optical coincidence rangefinders available (I found a couple on ebay) but they were firmly in the "cheap" category and not something I'd really trust.

I would also like to see a small, accurate coincidence rangefinder good from say 100-2000Y with magnification somewhere in the 20-40X range. I do a lot of ground squirrel hunting on flat crops where there are no objects large enough to get a laser to return an accurate range because there's nothing but flat ground between you and the targets. Our little squirrels (about a 6-9" body length) don't make good targets for a laser rangefinder and their mounds (if they even leave one, typically it's just a hole to their burrow) are also too small to get a range back from. That leaves either guessing or trying to mil the little buggers in the scope.

The old Wild Heerbrugg artillery rangefinders do work well beyond 300M but as you said it's not really quick to setup and use. A small unit about the size of a pair of binoculars with magnification somewhere in the 20-40X range that worked from 100Y out to 1500Y or 2000Y would be on my "must buy" list for ranging things that are either too small or terrain-limited for a laser rangefinder.

 

[Redmanss]

Re: Optical rangefinder: Why not?

You can always just mil out your target and match it against a Mildot Master for your range. Not very effective once you get past 700yds as your margin of error is extremely slim then, but still effective enough for most uses.

Get a good spotting scope with a reticle, Leupold MK4 or similar, and have that be your backup. A good FFP scope with a decent top end power is just as good too.

Or just get a Vectronix Terrapin. Haven't seen much feedback as far as use in inclement weather, but it sure smokes the competition in everything else.

 

[Kiba]

Re: Optical rangefinder: Why not?

I've already got a Razor HD Spotter with the 30x mil reticle which is very helpful-- but often times it's still hard to get an accurate mil-estimated range of a small squirrel. I can usually get close enough and then make corrections after the first shot. Within 300 yards it's not a problem, it's the squirrels at 300+ that I try to go for that are more difficult.

On the flatlands with no objects of any meaningful height to get a laser return from it's hard to get an accurate reading back from any kind of laser rangefinder. That's where an optical coincidence rangefinder shines; just turn the knob until both images converge and that's your range. No milling needed, no need to find an object large enough to get an accurate laser reflection back from.

I will probably pick up a Terrapin to try but in the flatland squirrel hunting situations I have my doubts it will be any more effective than my Bushnell Fusions because of a lack of any objects with a meaningful height above the flat ground to get a return from. Milling the little bastards with my scope or Razor spotter usually gets me close but an optical rangefinder would make quick and accurate work of it-- and it would be nice to have the optical option available.

 

[jlow]

Re: Optical rangefinder: Why not?

I think the reason is size and weight.

The accuracy of any optical rangefinder is dependent on how well it is made and the distance between the two reference optics. The further they are apart, the more accurate. This is the reason why those artillery RF are so big.

With an increase in size, you have increase in weigh and decrease in portability. The technology was already very mature by WWII but you won’t see small optical RFs for that reason.

 

[rg1911]

Re: Optical rangefinder: Why not?

I understand that you need a certain base length to get an accurate reading. However, for a max range of, say, 2000 yards, the base should be significantly shorter than the almost 4-foot length of the artillery rangefinder. Not to mention lighter.

Although we don't have Kiba's ground squirrels, we have lots of prairie rats. Getting a laser to range a mound past rock-throwing range is an exercise in futility.

I may have to see if I can get an answer from one or more of the optics companies.

Cheers,
Richard

 

[Outdoorsman9]

Re: Optical rangefinder: Why not?

Vortex Recon R/T 15x50 ---> http://www.vortexoptics.com/product/vortex-recon-rt-15x50-tactical-scope

 

[Spuhr]

Re: Optical rangefinder: Why not?

I was told that the calibrationtolerance was within 10%.
Despite that I actually have a number of the optical rangefinders I havent played around with it enough to know if the 10% is a valid number or not.

But you should probably ask yourself if you can accept 10% or not.

Håkan

 

[bobtodrick]

Re: Optical rangefinder: Why not?

As mentioned above...size and weight.
The optical rangefinder found in Leica cameras is probably the best 'small' rangefinder...in that it's small enough to fit in a camera body.
But the mirror and prism are only and inch or so apart...and this means that anything beyond about 50' is classed as 'infinity' (which is as accurate as a camera lens needs).
To be accurate at the distances we are talking the mirror/prism would need to be far apart (check the rangefinders on battleship main guns...they're feet apart).
Just isn't really feasible in a light, small, relatively inexpensive package.

 

[Layton]

Re: Optical rangefinder: Why not?

I would think that if it was feasible for the kind of accuracy you would need at the ranges given it would have done by know given the technology has been around a whole lot longer than lasers.

L

 

[JL]

Re: Optical rangefinder: Why not?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RG1911</div><div class="ubbcode-body">
So my question is: Is there a purely optical rangefinder available? And if not, why not?

I have one of the large, old Swiss artillery rangefinders, but it's not what I'd call portable. And I don't often need to range out to 20-thousand meters.

But it isn't bothered by any of the things that affect laser rangefinders and it doesn't have electronics that will self-destruct in a few years.
</div></div>
Google"theodolite" and "stereoscopic rangefinder".
Not all can use stereoscopic devices, but system works. Original usable condition are still available, for instance reasonable sized WWII germans such as 80cm long (about 1 yds) are still for sale. I recall that size was commonly used by Kriegsmarine U-Boots.

 

[TiroFijo]

Re: Optical rangefinder: Why not?

One advantage of stereoscopic rangefinders is that they don't depend on an EXACT, KNOWN, objet size. You must have good stereoscopic sight (in your eyesight), then just get a clear picture and calculate the range.

With a good mil based reticle and high magnification scopes you can range very accurately <span style="font-style: italic">IF you know the exact object size</span>, and if the object is large (vehicle lenght, door height, etc.), much better. The smaller objects are not good for accurate ranging, one meter is just 1 mil at 1000 m, and even a small 0.05 mil reading error is a 5% range error at this distance.