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.
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.
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.
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.
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.
