Optical Rangefinder

[OnceFuturePoly]

Please forgive the off-topic question, but I've found the wide variety of Literotica followers know something about virtually everything!

My dad had a little optical range finder he used with his camera to estimate distances. Look through the viewport, turn a knob to align two images until the object you are interested in superimposes. Then read the distance off a dial.

Not very accurate, and 50 feet was right next to infinity on the dial. But it was cheap and useful for estimates.

Much searching on the internet can't find anything that isn't a piece of electronics well over a hundred dollars. A couple of $20 exceptions are for Golf, and optimized for distances 50 yards (45 meters) and beyond.

I want one that will work with trees -- how high (far above me) is this limb or fork? -- say 10 to 100 feet. (3-30 meters).

How can I find such a range finder, pray tell? Thanks!

 

[Weird Harold]

Please forgive the off-topic question, but I've found the wide variety of Literotica followers know something about virtually everything!

My dad had a little optical range finder he used with his camera to estimate distances. Look through the viewport, turn a knob to align two images until the object you are interested in superimposes. Then read the distance off a dial.

Not very accurate, and 50 feet was right next to infinity on the dial. But it was cheap and useful for estimates.

Much searching on the internet can't find anything that isn't a piece of electronics well over a hundred dollars. A couple of $20 exceptions are for Golf, and optimized for distances 50 yards (45 meters) and beyond.

I want one that will work with trees -- how high (far above me) is this limb or fork? -- say 10 to 100 feet. (3-30 meters).

How can I find such a range finder, pray tell? Thanks!

Most of the new purchase optical/double image rangefinders now available seem to be in various "rangefinder cameras."

If you really want one like your father's, you'll probably have to haunt places dealing in antique photography equipment -- estate auctions, e-bay, auction houses, yard sales, pawn-shops, etc.

My late father and my late father-in-law both had photography rangefinders like you describe, but I have no idea who inherited them or where they might have wound up.

ETA: http://camerapedia.wikia.com/wiki/Rangefinder_(device) -- that page has some good info and images.

 

[rthnck]

Well if you have an iphone or an ipad there are range finder apps (free or a couple of bucks) that may be worth a shot.

 

[iamincognito45]

I don't think the cheap golf range finders will be what you want. I am pretty sure they are used primarily for approach shots to the green and are based on the flag sticks being the same height. So the range finder is not really a range finder but measures the apparent height of the flag stick to gauge the distance. So it would be useless for judging the height of trees.

What I have learned about optics is 'you get what you pay for'. For hunting, it's is not uncommon to spend as much on a scope as you spend on the rifle underneath it.

I would recommend a mid range optical range finder used for hunting (either bow hunting or rifle hunting). The need for accurate ranging for hunting will be as accurate as you need for your application.

Good luck!

 

[Bramblethorn]

I don't think the cheap golf range finders will be what you want. I am pretty sure they are used primarily for approach shots to the green and are based on the flag sticks being the same height.

Yep, I'm having trouble thinking of any way a monocular camera-based rangefinder would work for long distances without having a known reference object for comparison. For very short ranges you could use the focus to estimate it, but that's not going to work for longer distances.

 

[Que]

Try militaria dealers. It would be a very cool thing to have.

Unless they were made in far larger numbers than I would expect, they might be pricey though.

Vietnam era snipers carried something like you described. It might well pre and postdate that conflict.

 

[Weird Harold]

I would recommend a mid range optical range finder used for hunting (either bow hunting or rifle hunting). The need for accurate ranging for hunting will be as accurate as you need for your application.

I think even that is going to be too long range for what the OP wants -- he's looking to range distances under 100ft (30 meters or so) and that's in the range of photography/camera rangefinders. Also, the main problem is finding a "new" rangefinder that is purely optical and mechanical -- ie doesn't require batteries or recharging.

 

[oggbashan]

Edited to add: I have just looked on eBay UK, under Cameras and Photography for 'rangefinder'. I found several optical ones produced by Voigtlander - but they are so small that I doubt they would be very accurate. See below about distance between lenses. The Voigtlander's separation appears to be an inch!

http://1.bp.blogspot.com/_VmQdhWOpQdU/SuD47Be-9AI/AAAAAAAAAJk/fXydfdjdQVg/s320/voigtlander+rangefinder_002.jpg

http://www.rs-photographic.co.uk/shopimages/products/normal/u2837.JPG

The Russians produced and sold widely a set of Leica clone rangefinder cameras in the 1960s and 70s. They were wholly mechanical 35mm cameras.

They were sold under names like Zorki and Fed. If you look on eBay you might find one.

http://www.thecamerasite.net/02_Rangefinders/Images/Zorki-4-K.jpg

All Rangefinder cameras, including Leicas, suffered from one problem. The distance between the two points used to provide the rangefinding effect was too short, a few inches.

Real military optical rangefinders only became useful with a distance of about three FEET between the lenses. WW2 and earlier battleship rangefinders gradually increased the separation between lenses to six feet, twelve feet, eighteen feet...

Edited yet again.

Optical rangefinders, whether a stand-alone or a camera, work best with a clear vertical element at the distance to be measured. That is why golf rangefinders tend to be used pointing to the flag pole. A vertical isn't essential but is the best choice, otherwise a clear division in the image at the point to be measured. For measuring a distance to a person, the edge of their body is preferred instead of their centre.

During WW1, some warships added optical baffles between and around their funnels to confuse opposing ships' optical rangefinders. It might have made the operators' task slightly more difficult by a matter of seconds - long enough to fire first!

 

[Que]

Oh wait!...

I was answering the question instead of solving the problem...

for what you want to do, foresters have a tool..

you can either pace the distance to the tree or measure with a tape, but there is a sighting device that you simply look through as you walk backwards from the tree...

when the branch, crown, bird's nest or whatever it is you are measuring is in the 45 degree angled sight...it is exactly the distance to the tree plus the ocular height of the viewer.

edit: its a clinometer...the above was probably an invention I created as a kid having seen a clinometer...mine is no less accurate and cheaper.

From: The Maryland Envirothon.


" Tree height is measured using the principle of triangulation with a clinometer. Of all the forestry tools you will use, the clinometer requires the most practice and skill. Assuming that the tree grows at a right angle to the ground (even on a slope), we use the clinometer at 1 chain (66 feet or 19.8 meters) away from the tree using the following steps:

With both eyes open, aim the black crosshair of the clinometer level with the base of the tree at the soil. Using the right-hand scale (the left scale is for measuring percentage of slope) you will read a “negative” number if the tree is on level ground or down slope. You will read a “positive” number if the tree is up slope.

http://www.dnr.state.md.us/education/envirothon/forestry/blackcrosshair.gif
With both eyes open, aim the black crosshair of the clinometer to the top of the tree. This is a tricky measurement because your view may be obscured by leaves or nearby tree branches. If the top of the tree were an open umbrella, you’d want to be aiming at the point on the top of the umbrella.

The Clinometer.http://www.dnr.state.md.us/education/envirothon/forestry/clinometer1.gif Aim the clinometer with both eyes open.http://www.dnr.state.md.us/education/envirothon/forestry/clinometer2.gif"

 

[Weird Harold]

Edited to add: I have just looked on eBay UK, under Cameras and Photography for 'rangefinder'. I found several optical ones produced by Voigtlander - but they are so small that I doubt they would be very accurate. See below about distance between lenses. The Voigtlander's separation appears to be an inch!

http://1.bp.blogspot.com/_VmQdhWOpQdU/SuD47Be-9AI/AAAAAAAAAJk/fXydfdjdQVg/s320/voigtlander+rangefinder_002.jpg

That appears to be just what the OP needs:

I want one that will work with trees -- how high (far above me) is this limb or fork? -- say 10 to 100 feet. (3-30 meters).

 

[OnceFuturePoly]

I spend an afternoon messing with Android apps for measuring angles and distance through the camera -- even put an 8' 2x2 on a stand and painted the ends to give known reference to work with. Bottom line, nothing (free) is usable.

Also sought out a Clinometer in the internet shopping wastelands -- $25 for simple mechanical ones, or spend several hundreds for the fancy electronic ones.

Found lots of instructions involving a protractor, soda straw, glue, string and fishing weight. Problem is reading the angle off the protractor while looking down the inside of the straw.

Considered building a clinometer, but my parts (junk) bins didn't have enough for a good starting point. I suppose I could visit my cousin the machinist...

Finally, I broke out my camera tripod and stuck a soda straw on it. Borrowed a 100 ft tape measure from my neighbor, and used the bubble level/plumbbob feature of my GPS app to measure the angle of the straw.

A retreat back to my old CRC Math book for trig formulas, a spreadsheet, and I got my estimates.

BTW, the picture oggbashan posted looks a lot like I remember!

 

[OnceFuturePoly]

Inspired Gerry-Rig:

A couple of pieces of v-channel, one sliding inside the other for adjustable length.

Two laser pointers, securely fixed each to a piece of channel, and aimed to cross (dots meet) at a far distance. Sliding the channels together to shorten the distance between the pointers makes the dots converge at a closer distance.

Take a one time calibration, but you can get a long parallax so it can be pretty accurate.

 

[albertaboy]

Buying a used Bushnell or Nikon Laser Rangefinder shouldn't be too expensive.

Under 100 yards they work great, only the more expensive Leica's work must past 300 yards on small objects.