Rangefinders

© Brooke Clarke 2009





Background
How They Work
Equipment
    Bushnell Golf Yardage Pro 400 Binoculars
    Laser Technology Criterion
    Prexiso X2 Laser Range Finder
Links

Background

There are many applications for range finders (Wiki) such as: photography (to adjust the lens focus), golf (to determine what club to use), military (adjust weapon for range and target designation), rifle scope graticule (known height) etc.

How They Work

Radar, Sonar & Optical Pulse

These are "time of flight" systems where the round trip propagation time is measured and divided by twice the propagation velocity.

Optical

The oldest optical system is based on the concept of stadia.  The idea is that you can determine distance by measuring the included angle of an object of known height.
Examples: K&E 76 0000 Alidade, Leitz 115A transit

Another system is based on the "split image" that's made to align by rotating a mirror.  The difference in angle between the two mirrors can be solved based on their separation into the range.  This is the method used by "rangefinder" cameras and the military rangefinders that look like a drain pipe as well is civilian rangefinders like the hand held
Edscorp Field Range Finder.

Image property range finders are used in modern digital cameras.  One way these work is to look at the image contrast as the lens is set a various focal lengths.  The highest contrast image is deemed to be the best focused.

Time of flight is used in modern digital optical range finders like the Busshnell golf binoculars and the Laser Technology Criterion units.  These typically have one lens for the outgoing pulse of IR light and a separate lens to focus the light on a fast photo sensor.

Equipment

Bushnell Golf Yardage Pro 400 Binoculars

One objective lens is for the IR transmitter and the other is for the IR receiver.  There is a small visual telescope in the center that's for the operator to observe where the spot is pointing.  The two large lens are black in color, not clear like optical binoculars.  The range is displayed in units of either meters or yards, a little to coarse for surveying.

Bushnell Golf
                Yardage Pro 400 Binoculars
Bushnell Golf
                Yardage Pro 400 Binoculars



Laser Technology Criterion

This is the model 400 that includes tree measuring functions.  The range is displayed in 1/100 of a meter, i.e. a cm which is less than 1/2" so are excellent for surveying.  In fact part of the set is a fork mount that fits a standard surveying tripod.

Operation

After power on you will see one of the top menus.  Use the up or down arrows to scroll to the desired menu.  In my case they are:
TREE
CONDUCTOR CLEARANCE
SURVEY
SYSTEM
TREE
Once you have selected the appropriate top menu press the ENTER button. For Example:

POWER (on)
<down>
<down> i.e. SURVEY
ENTER i.e. BASIC MEASUREMENTS
ENTER display is:
HD:-------.-- M
AZ:------.- DEG
<press trigger>
display blanks change into data and pressing up or down scroll arrow shows more data like inclination, slope distance, etc.

When in Survey measurement mode and the trigger is pressed you hear a buzzing sound as the laser range finder and other sensors are working.  When aimed at a wall about 4 feet away the spot size as viewed using the PAS-6 IR scope is about an inch high and half an inch wide.

Laser
                Technology Criterion
Laser
                Technology Criterion
Laser
                Technology Criterion




Prexiso X2 Laser Range Finder (Manual, Specs)

Prexiso X2 Laser Range
          Finder

eBay search term: "Prexiso X2".  Price range: $100
Range: up to 98 feet with 1/16" resolution (or) 30m with 1mm resolution.
Pressing + or - between distance measurements allows adding or subtracting them.
To measure [Area - Volume - Triangle] press the key [once, twice or three] times prior to making a measurement.
The upper left of the LCD shows the reference plane: either the front or back (shown in photo).  Pressing the units key toggles between front and back.
Pressing and holding the units key gets you into the units mode.

Outside in the daytime it's difficult to locate the red laser pointer spot on natural vegetation.  Getting the spot onto a 5 gallon white plastic paint bucket at 30 feet is difficult.  But when you press and hold the "Laser On" button for a few seconds to turn on continuous measure mode it's easy to start close to the bucket and back away while maintaining the spot.  It might be easier to use outside at dawn or dusk.  Need white or reflective targets, not trees or bushes.

Links

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