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Rangefinder Tip O' the Day: Laser beam divergence effects

I've been digging around trying to find manufacturer specifications on laser rangefinder laser beam divergence. Most laser rangefinder beams are elliptical/rectangular. To the user, this means that orientation of the laser with respect to openings in the forest canopy through which one is shooting through becomes relevant for most rangefinders. From the documentation that I have been able to find, Swarovski and Laser Technology laser beam horizontal and vertical divergence is symmetrical, so orientation of the rangefinder is less important. Optilogic and Bushnell YardagePro rangefinders are vertically oriented while Leica, Zeiss, and Nikon rangefinders are horizontally oriented. If you are using an assymmetrical laser beam and you have trouble shooting through a small opening in dense foliage, try rotating the rangefinder 90 degrees and trying again. Try aligning your rangefinder parallel to the shape of an elongated opening and then 90 degrees to it to see which works better, if at all. It might not make a difference in most cases of irregularly small openings, but in cases of long narrow openings it might save you from running around looking for a bigger opening. When practical for shooting through brush at the base of the trunk, all laser rangefinders are aided by the addition of reflective target surfaces (white paper or prismatic reflectors, not flat mirrors).

In addition to laser beam shape, the laser beam size also varied greatly. I'm listing those that I found here in order of smallest to largest in units of millirad. At 100 yards, 1 millirad is equal to 3.6 inches. I assume symmetric beams are circular and elongated beams are rectangular. The listing of beam divergence is in the format of horizontal x vertical = beam area follows:

Zeiss, 1.6x0.5=0.8
Leica LRF and CRF series, 2.5x0.5=1.25
Optilogic LH series, 1.1x2.8=3.1 (based upon beam footprint given at 100yds, not on divergence stated.)
Swarovski, 2x2=3.14
Nikon 550's and Laser 800S, divergence unknown, beam is about 4.5-5x wider than it is tall, this is the only 870nm laser in the group.
Laser Tech Impulse, 3x3=7.1
Bushnell YardagePro, 2x4=8

It's worth noting that most lasers are comparable 904-905 nm infrared lasers. Wavelength in our application should have negligible effect. Nikon lists beam divergence of the laser diode that is used, but not the final value including it's optics. The value listed by Nikon is clearly larger than what has been observed in the field, so it is not included numerically here. From online comparisons with other rangefinders, it appears that Nikon's beam divergence is definitely larger than Zeiss, Leica, or Swarovski. Perceptions to the contrary are likely due to specific conditions in combination with signal processing or algorithms within the rangefinder and not due to the actual laser beam divergence. I could not find detailed information for Leupold or others but note that Leupold now has the smallest rangefinder on the market. Good shootin'!
by pauljost
Thu Aug 12, 2010 4:48 pm
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Drummond Woods

On August 22, Lee Frelich and I visited numerous sites across northern Wisconsin. Our last stop was a site that was described by Forest Stearn in an article in the April 1951 Journal of Ecology, Volume 32 Number 2 entitled "The Composition of the Sugar Maple-Hemlock-Yellow Birch Association in Northern Wisconsin." I had read it many years ago and visited it once at dusk but could not make out much in the twilight. It is far west of my normal travels in the Chequamegon National Forest, so I haven't had a chance to revisit it until now. It was recently declared the Drummond Woods State Natural Area and dedicated to the memory of Forest Stearns, one of the driving forces of Wisconsin's State Natural Area program. It is located on the northwest side of US Highway 63 where the North Country Trail intersects the highway and is at an elevation of approximately 1270-1280 feet above sea level. Approximately one mile north of Drummond in southwestern Bayfield County on US 63, there is a small parking lot and trailhead within site of US 63 on Chequamegon National Forest Road 235 (Old US Highway 63.) This location is approximately 18 miles north of the Uhrenholdt Memorial Forest pines that Lee occasionally visits at US 63 and County Highway OO in Seeley, WI. I have no pictures since I had forgotten my camera and my old camera phone takes poor pictures.

The Drummond Woods was set aside by the Rust-Owen Lumber Company in the 1880's when it's workers requested that some virgin pine forest be saved for their families' recreation in the nearby company-owned mill town of Drummond, WI. Most of the grove stands to this day. It suffered some wind damage in 1941 and by 1951, only three large pine stumps showed signs of early logging. Here is a picture of the nearby area from past, although likely not of the Drummond Woods site:

One tree, called the King Pine, was struck by lightning in 1967 and suffered wind damage in 1977, then died in 1978. It was cut down and estimated to have provided 2500 board feet of lumber from it's 43 inch DBH and 110 foot height. One fourteen foot log scaled 700 board feet. It's rings were counted to 265 years at a height of 7 feet. The rotting stump remains to this day and is marked with a sign along the trail.

As we entered the trail, we were immediately welcomed by a large, topped American Basswood with a girth of 126 inches or 10.5 feet, or 40 inch DBH. It had a minimally tapering column shaped trunk that was topped at about 50 feet and had sprouted back up to around 70' tall.

A large diameter white pine is obvious along the west side of the trail near the top of the hill. It had a 134 inch or 11.2' girth, nearly 43 inch DBH. The height was measured at 118 feet. This is pretty close to the size of the grove's previously documented King Pine.

The largest diameter white pine is visible just east of the trail with beautiful gray bark when sunlit. It stands out among the others with it's 140 inch or 11.7' girth, nearly 45 inch DBH. The height was measured at 119 feet. This tree clearly surpasses the size of the grove's previous King Pine.

Another large white pine is west of the first pine near the bottom of the hill. It was also 119 feet tall but had a girth of 118 inches or 9.8 feet.

Other shorter pines exceeded a height of 100 feet, but none of the hemlock passed 100 feet. It was a nice hike to finish the weekend.
by pauljost
Sun Aug 29, 2010 11:41 am
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Northern Highland American Legion State Forest Pines

The weekend of August 21-22, Lee Frelich and I explored parts of northern Wisconsin. We were invited to visit a grove of pines found by Jim Baker of Mercer, WI and his daughter Becky Boquist. She had emailed Bob Leverett after finding ENTS' web site while searching the internet for information on Wisconsin's biggest white pines to see how the pines that they had found compared to the biggest known. After leaving home, I realized that I had forgotten my camera. My camera phone does not take decent images, so forgive my lack of pictures here.

Saturday morning, I awoke to a loon calling outside my hotel bedroom window. As Lee and I drove into town for breakfast, we passed a giant fiberglass loon statue with a sign declaring Mercer as the loon capital of Wisconsin. After breakfast, Jim and Becky met us at our hotel and led us down roads into Wisconsin's Northern Highland - American Legion State Forest in southeastern Iron County, Wisconsin, just east of Mercer, Wisconsin. We parked on the roadside and hiked down an old logging road to where it ended near a marshy bog. We crossed the alder marsh and bog in our rubber swamp boots and climbed up a small rise in the swamp to an island of old growth maple-yellow birch-hemlock with some paper birch, red pine, and clusters of super-canopy eastern white pine. I should have counted the pines, but didn't! There were probably about 12-15 large white pines in a compact grove of 1-2 acres on the northern half of the 7 acre oblong island while there were numerous smaller pines in another 1-2 acre grove on the southern half of the island.

The biggest pines were in a compact grove in the top center portion of the island in the image below at an elevation of just over 1610 feet. The cluster of larger crown diameter pines casting bigger, darker shadows is relatively easy to make out in this picture from, numerous other sites' imagery of this area was of poorer quality:

They showed us the thickest and most visually impressive one of the bunch which we named the "Jim Baker Pine", after it's discoverer. I measured it's girth to 155 inches or 12.9 feet at 4.5' above the estimated point "where the seed sprouted" considering the surrounding soil that had been uplifted by sprawling root buttresses. That's over 49 inches DBH, or in diameter at breast height. It had a small burl about 4' off the ground so the height measurement did not have to adjusted much as the tape laid just above the top of the burl. The height of this tree was measured at 119 feet.

Here's a picture that Jim Baker took of his daughter and the pine on a previous visit:

It was clearly the thickest of the bunch and quick measurements of the surrounding super-canopy pines showed most to be up to 11 feet in girth and 100-120 feet tall. However, two stood out to me to be a bit taller.

The first one that I singled out was near a non-destructively mounted deer hunter's tree stand on a nearby hemlock tree at the northeast corner of the grove. It had a few hemlocks and pines nearby that forced height measurement from only one direction to the east. It ended up being measured at 131 feet tall with a girth of 134 inches or 11.2 feet.

The other one I noticed on the our amblings through the grove but I couldn't clearly see it's top from any place on the ground. It had the freshest lightning scar of any tree in the grove. If lightning picked it out and it looked to be tall to me before I noticed the scar, I figured it had to be worth measuring. On the way out, I stopped to give it one more try. Finally, finding a hole through the canopy with a view of the crown from the east, I measured it to 134 feet tall with a girth of 136 inches or 11.4 feet.

These trees were a great find. They are the tallest known pines in Iron County where I have struggled to find any pines over 120 feet in the past. With the recent deaths of the largest diameter previously known single-stemmed white pines in state of Wisconsin, this is a close third place girth in ENTS measured living Wisconsin white pines. Second place is held by a 13.0 foot girth (165' tall) white pine in the Menominee Reservation and first is a 13.2 foot girth (154' tall) white pine in the Nicolet National Forest's Cathedral Pines grove.
by pauljost
Sun Aug 29, 2010 10:45 am
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Cathedral Pines

On September 4, 2010, my wife, my son, and I visited the Cathedral Pines grove in the Nicolet National Forest near Lakewood in northeastern Wisconsin's Oconto County. I intended to remeasure the two tallest known eastern white pine trees in the grove. The area is a virgin grove that was set aside by the Holt and Balcom Logging Company around 1880 when Lucy Rumsey Holt, the wife of W.A. Holt, the company president, asked that the tract be spared so that she could continue to conduct bible study classes with her children there. Pines are now reported in the 200-400 year old range.

The grove is a part of a larger State Natural Area and has a popular hiking trail looping through it. It is the largest dense white pine grove in Wisconsin and is dominated by eastern white pine with many in the range of 9-10 feet in girth and 125-135 feet tall. There are some red pine to 90-100 feet tall and many hemlocks under 100 feet. The forest also contains a significant beech-maple-yellow birch component along with some red oak, aspen, as well as some other trees. The entire approximately 22 acre virgin pine grove is at an elevation of approximately 1340 feet, plus or minus 10 feet. With over 100 nests, a great blue heron rookery's droppings are killing off the taller trees on the highest ground but make for an enhanced experience during visits in May and June before the fledgelings leave the nests in early July. It is a nesting site for ovenbirds, blackburnian, magnolia, and pine warblers, The best time to visit for tall tree hunting is mid-October through the first week of May when the deciduous sub-canopy is not a visual obstacle. On the coldest winter days, visitors are virtually nonexistent while the grove effectively tames light winds so that the bitter temperatures are more tolerable.

I had spent a few days in December of 1999 scouring this grove for it's tallest trees. During that visit, overnight lows approached -30 F with highs around -10 F with fresh unbroken knee-high snow on the ground. With no other visitors, I was able to use GPS, compass, and my footprints in the snow to walk a near perfect grid throughout the entire grove and then the surrounding forest. After finding dozens of trees in the 130-140 foot range, I then started ignoring trees that were under 140'. In the northwestern part of the grove, I found the only two trees whose tops I could reach with laser that exceeded 140 feet in height. One was 145.4 feet tall with a 112 inch girth and other one was 149.6 feet tall with a girth of 127 inches. With a little more searching, I was able to get a height of 150.2' on the bigger one. This proved to be the only tree in Wisconsin that I have measured over 150 feet tall until Lee and I hit 165 feet on a 13 foot girth white pine in the Menominee Tribal Enterprises private reservation forest about 20 miles southwest of the Cathedral Pines. In 1999, I was measuring pine girths at 4.5 feet above the highest contact point with the earth. Unfortunately, on the biggest tree there was some taper, so my incorrectly high point of measure reduced it's girth considerably from what would be expected. Additionally, I misread my original notes. The tree was not 127 inches but was 12' 7", with my notes showing a faint dent where the pencil lead had broken when making the foot mark, '. Soon after, I was tutored by ENTS on ignoring earth upheaved by centuries of root growth and instead examine the immediate surrounding terrain for the expected point from which the seed would have sprouted.

On this trip, I took the direct route to these trees. We headed downhill along the road from the Cathedral Pines trailhead parking lot. When the road hit it's lowest point in the immediate drainage, we headed to the north following the lower limit of the drainage and walked it up right to the trees where the dense underbrush opens up to an open forest floor under a dense hemlock canopy with a white pine supercanopy. We found a dense 100 square foot patch of spotted coralroot orchids that had just finished blooming. I noticed that a trail had been cut to within about 40 yards of the trees that was a short loop extension leading to the groves "Cathedral" area somewhat to the southeast of these trees. The main loop on the hill in the grove had been graveled over. I hope that there is no limestone content in that gravel, but, unfortunately, I am a poor geologist.

This time, using girth measurements to proper ENTS standards, I was pleasantly surprised by the numbers that were obtained. Now, the thicker tree had a height of 154.3 feet and a girth of 158" = 13.2 feet or over 50 inches DBH. This is the largest girth of a single stemmed tree measured by ENTS in Wisconsin that is still living. The height measurement was from the place of the lower previous measurement since the sub-canopy obscures the top from the other place of measurement at this time of the year. This showed a height increase of 4.7 feet over 11 growing seasons. The thinner tree is about 10-15 yards west-northwest of the thicker pine. The thinner tree had a height of 154.8 feet and a girth of 124 inches = 10.3 feet. This is a height increase of 9.4 feet in 11 growing seasons on the younger, thinner tree.

These are the two tallest white pines in Wisconsin outside of the Menominee Indian Reservation. The next time that I return to the Cathedral Pines, I might try to relocate a 7.5 foot growth white pine that had bent over from heavy snow and had a curving trunk length of about 160'. Also, there are some other pines near the two that I measured that are now probably over 140'.

by pauljost
Mon Sep 06, 2010 9:21 pm
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Partitioning Diversity

The Journal of Ecology's editor opened a 30 page forum to debate on my brother Lou's papers on proper usage of diversity indices. The editor also made the announcement that my brother's 2007 paper may be the greatest advancement in measuring diversity for ecology since Whittaker's paper 50 years ago!!! My brother, Lou, is really excited about it! I've attached the editor's comments and like to brag about my brother a bit...


Paul Jost
by pauljost
Mon Aug 02, 2010 11:27 pm
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Re: Partitioning Diversity

I have a brief update. Because of Lou's recent achievements ( , our family has just been told that Lou has been awarded the virtual equivalent of an alumni of the year award for 2011 from Lawrence University, . It has not been formally announced, but is described as follows:

"The George B. Walter '36 Service to Society Award
This award is presented to recognize alumni of Lawrence University or Milwaukee-Downer College who best exemplify the ideals of a liberal education through socially useful service in their community, the nation, and/or the world. This award honors George B. Walter '36, alumnus, faculty member, educator, and dean of men, whose work at the college and beyond promoted his conviction that every individual can and should make a positive difference in her or his world."


by pauljost
Fri Dec 24, 2010 12:43 pm
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Re: Mobile Phone Mod for BBS

Hey Ed,

I replied on my Droid3 and it looks good here, but I'm not sure that it is much different from the normal web page. It is scaled properly to the smaller screen though and everything seems to work fine, too.

by pauljost
Tue Dec 20, 2011 11:26 pm
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