Laser tests   Robert Leverett
  Jan 18, 2006 11:11 PST 


      It is easy to always trust your laser rangefinder. But constant
checks and new calibrations are a part of our craft. The table below
contains the results of a test conducted in a light rain using two
lasers, an old Bushnell 800 meter/yard model, which I have always
regarded as my most reliable LR, and my Nikon Pro Staff 440.
Interestingly, the Nikon shoots half a yard shorter to a bright target -
at least in rain.

      When shooting a trees on which I want to achieve high accuracy, I
use both lasers, shooting multiple times in different lighting, and
ultimately settling on a measurement that I think I can defend. If I'm
not looking for extreme accuracy, I just use one laser.

      I'll repeat the test below in sunlight and report the results for
the stationary objects in the list.


In rain/drizzle
                      Yds      Yds
Target                       Bushnell Nikon

Wall of bldg next        75 75.5
    to sign - dark
Sign on wall-bright         75 75

Wall of bldg adjacent     75 76
   to a sign - dark
Sign on wall-bright         75 75.5

Base of pin oak-dark     79 79

Red car door-fairly bright 36 36.5

Base metal light pole - dark 54 55

Bright yellow pipe #1     55 55.5

Bright yellow pipe #2         42 43

Bright yellow truck      71 71.5

Metallic gray car door         76 76.5

Yellow sign                103 104

Beige Building side        157 158

White shade in window        154 154

Red taillight                 32 32
Immediately adjacent         32 32.5
to taillight

Tip of white pine        102 103

Avg                         76.06 76.62

Robert T. Leverett
Cofounder, Eastern Native Tree Society
Re: Laser tests
  Jan 18, 2006 12:57 PST 

Of course, in any such comparison, I will pipe in that you should get a more
accurate distance measurement using a reflector than you would surfaces with
less accurate reflectance values...what were the actual (measured by steel
tape, for example) of the red reflector?
RE: Laser tests   Robert Leverett
  Jan 19, 2006 06:45 PST 


   For shooting to the trunk, reflectors are often practical. Of course,
they don't apply to crown shots. We're usually shooting multiple tops of
the crowns of trees to find the highest top. So we need to know how our
instruments perform under less than ideal conditions.

   Though less tahn ideal is a given for crowns, less than ideal often
applies to trunks as well. Sometimes we're on the opposite sides of
streams from the trees or the trees are in dense rhododendron or laurel
thickets. On very important trees, I do often place a more reflective
object on the trunk of a tree and shoot it as opposed to the darker

   With respect to the lasers, my objective was to test them under
typical field conditions where the targets have different
reflectivities, where atmospheric conditions vary, the surface of the
targets are different (rough, smooth, etc.), and where distances to the
target vary greatly. So, I upped the number of tests to 32 with
distances from 21 to 152 yards. Conditions varied from rain to cloudy to
partly cloudy to sunny. Targets were of all types and textures. Under
this wide range of conditions, the average difference over all distances
between the lasers stands at 0.95 feet and the difference is partly due
to the fact that the Nikon reads to the half yard and the Bushnell to
the whole yard. Shifting around showed me that if I got to click over
point in each case, the 0.95 feet went down to an average of about 0.5
feet. So over the wide range of fiend conditions, the two lasers are
pretty close. Results are closest at the shorter distances. At disatnces
of 40 to 80 yards, the average distance without adjusting for click-over
is 1.0 feet. Getting to click over reduces this to about 0.5 feet.

   Tests of lasers calibrated on changes of 1 yard at a time to the same
target can give an incomplete picture. To understand on'e instrument,
one needs to use targets of different shapes and reflectivities and in
different atmospheric conditions. The full range of values eventually
show themselves.


RE: Laser tests comments continue   Robert Leverett
  Jan 19, 2006 09:43 PST 


   More thoughts on lasers and laser tests. Colby Rucker was a strong
proponent of eliminating potential error whereever one could. So, he ws
a strong proponent of controlling the error of eye-level to the ground
measurements by using a pole with a flag on it. Howard Stoner also make
good use of the pole-flag apparatus. It is the better way to go.

   Whether one employs a pole, a reflector, or a reflector on a pole, it
makes sense to reduce potential error on the lower traingle where that
can be done. However, I would emphasize that may measurers really don't
know their equipment well enough over the range of conditions they
encounter. There is variability among instruments due to:

    1. Shape of object,
    2. Reflectivity of object,
    3. Distance of object,
    4. Atmospheric condition between laser and object.
    5. Interference by surrounding objects.

   Of the 7 laser rangefinder I've owned, one Bushnell shoots long by a
yard (the 500 yarder) on the first measurement and then often settles
down to the right yardage. An older 400 yarder perpetually shoots short
by a yard. The other two Bushnell's are highly accurate. Or I should say
one is. The other had to be laid to rest. It went to laser heaven.

   The Optilogic instrument sucks, but is useful for very short
distances provided it has a wide and long unobstructed path to the
target. The first Nikon seemed okay, but is dead. It drowned. I don't
think it went to laser heaven, so I'll say no more about it. The second
Nikon is the one I've been reporting on. It is a good instrument that
picks up targets with more clutter around them than the Bushnell except
when the rain mode is invoked to shoot through brush. That mode doesn't
always work, but it is as effective as the Nikon, if not more so, when
it does work.

   The latest generation of lasers now beg to be tested. Wish I had one
of every make and model.


RE: Laser tests
  Jan 19, 2006 20:05 PST 

I agree with everything you said. I am certain that your comparisons as
provided were exhaustive (even exhausting?).

The 'fields' I would put across the top of the chart, to get at what you
haven't said, are (IN CAPS)
[natural target surface = nts; reflector = R; taped measure = tm):

nikon (nts) ~ bushnell (nts) ~ NIKON (R) ~ BUSHNELL (R) ~ actual (tm)

When running traverse in deep forest with Criterion 500, we would often turn
on audio signal...the Criterion would only pick up the reflector signal in
this mode, and only when it had enough for an accurate reading. Many times,
it would 'educate us' where the foresight (guy at the next point, with
reflector) would find it when we couldn't find it by naked eye. It
would seem to me to be a good feature for your lasers when in rhododendron
RE: Laser tests-back to Don   Robert Leverett
  Jan 20, 2006 05:48 PST 


No question about it, I'd love to have the features you describe.
Anti-rhodo and laurel capabilities would be sooper dooper. Howeevr, it
sounds like the Criterion 500 is pretty expensive. Do you know its cost?
Is/was it made by LTI? I think Van Pelt had a Criterion 400 and it does
a few things that his Impulse Laser doesn't do. At least that's what I
seem to remember him saying. I think he took diameter measurements with
his Criterion 400.

   BTW, my tests of the Bushnell versus Nikon don't identify the more
accurate of the two, just how one compares to the other. Over the next
few weeks, I'm going to bring out the old tape measure and do more

   One final point is that I could mimic my roving tests using your
ground level plan in all ways except possibly one - background lighting.
Shooting at the top of a crown with sky beyond presents a range of
lighting conditions that would be hard to duplicate shooting at ground
level. Dark target, bright sky, Bright target, dark sky (hmmm-tree on
fire?), bright target, bright sky. Dark target, dark sky. Any ideas?
There are times that my Bushnell shoots long by a yard when I go
slightly above the crown point. Why would I do this? Because dropping
the laser much beneath the crown point to get a fimer target also
introduces the problem of hitting forward thrusting twigs. One develops
a sixth sense about hitting forward thrusting targets, but then the
process of measuring becomes more art than science.