Monocular - Bushnell Legend Ultra-HD 10x 42mm

General discussions of measurement techniques and the results of testing of techniques and equipment.

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Re: Monocular - Bushnell Legend Ultra-HD 10x 42mm

Post by dbhguru » Tue Apr 10, 2018 2:09 pm

Don,

The Bushnell optics are clearly superior - definitely worth it in low light. I've bragged on Gizmo so much of late that he's starting to get a swelled lens. Yes, your discovery of this marvelous new toy was a very significant event.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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dbhguru
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Re: Monocular - Bushnell Legend Ultra-HD 10x 42mm

Post by dbhguru » Thu Apr 12, 2018 2:46 pm

Ents,

Yesterday, I measured a yardstick from an oblique angle at a distance of 66.5 and 66.667 feet to the opposite ends. The reticle reading was 46 as best as I could determine. It could have been 45.9, but not less. I got a length of 3.061. I later discovered that the reflecting tape I had put on the ends of the yardstick over-hung the actual end by 1/8". The difference between actual and measured was then 0.603 inches. I couldn't reduce that difference in repeated measurements. There may be some parallax effect from viewing the reticle over a large span.

Today, I tackled the yardstick again, but couldn't reduce the difference between actual and measured length. I measured the yardstick from exactly 30 feet away so that its ends should just cover the 50 to 50 scale or 100 units. The following images illustrate the way the experiment should have worked out. The first image shows what the M value in the formula should be, i.e. 100. That's 50 units on the left of the center line of the reticle and 50 units on the right. The specifications for the Bushnell say that one unit on the scale represents a yard (3 ft) at 1000 yards (3000 ft).

The second image shows what the Bushnell rule should translate to at 30 feet in terms of a full scale reading, i.e. M should be 100 at a distance of 30 feet to exactly cover the yardstick.
Screen shot 2018-04-12 at 3.06.07 PM.png
Screen shot 2018-04-12 at 3.06.07 PM.png (8.97 KiB) Viewed 380 times
Screen shot 2018-04-12 at 3.27.06 PM.png
Screen shot 2018-04-12 at 3.27.06 PM.png (15.6 KiB) Viewed 380 times
To put a finer point on it, I should have seen the 50 unit mark at the left edge of the yardstick, and the right end similarly. However, after aligning on the left side, the right 50-mark overlaid approximately the 35 inch spot on the yardstick, instead of 36. I don't know what accounts for this situation. Gotta figure it out. If there are zones where accuracy diminishes using the reticle, I need to identify them.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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dbhguru
Posts: 4462
Joined: Mon Mar 08, 2010 9:34 pm

Re: Monocular - Bushnell Legend Ultra-HD 10x 42mm

Post by dbhguru » Sat Apr 14, 2018 7:54 am

Ents,

One of the tests that I routinely perform on the Vortex, and now the Bushnell, monoculars measures the length/width of a target that is diagonally oriented in 3-dimensional space to the line of sight. The method developed to do the heavy lifting is that it requires 3 inputs: (1) direct distance to left side of target, (2) direct distance to right side of target, and (3) reticle reading for the target.

The question is how good is the method. The first of the two images below shows the formula used to compute the target width given the three inputs listed above. The second image shows the result of a test I ran yesterday. First the images.
TrapezoidDiagonal2Formula copy.png
TrapezoidDiagonal2Formula copy.png (12.98 KiB) Viewed 373 times
Now the test.
Screen shot 2018-04-14 at 8.09.29 AM.png
I expect that the accuracy of this method diminishes with distance and target orientation, not because of instrument accuracy, but because of the magnified impact of small errors in the input variables as distance increases and orientation moves farther away from 90 degrees. As of last evening, my friend Jared Lockwood agreed to help with sensitivity testing for this method. Hopefully, we can develop the methodology to reduce input errors.

As an example of what we are dealing with, Bushnell explains that one unit on the reticle scale equals a yard of target width at 1000 yards. Oh yes, I think they say approximate. We have our work cut out for us.

Is all this fuss over reticle measurements worth it? Maybe yes, maybe no, but I'm optimistic. I've recently been dealing with some pretty influential folks: Dr. William Moomaw, retired professor from Tufts University, and Dr. Mary Booth, an independent consultant. Both work on climate change issues and are very interested in carbon sequestration accounting. Bill has the official titles of Emeritus Professor of International Policy, Center for International Environment and Resource Policy and Co-Director Global Development and Environmental Institute, Tufts University. Both Bill and Mary support what NTS is doing in our modeling of bigger, older trees for volume because the results tend to support our contention that these big trees continue growing volumetrically long past what conventional wisdom would have us believe.

There is a very large difference between rates of growth for commercial purposes and for ecological ones. Apples and oranges. But the carbon models are mainly derived from plantation forestry, which concentrates on stand productivity, increases and declines, not individual tree growth. Where we have a grove of larger, older trees, those trees are holding a lot of carbon, and by our measurements, continuing to pack on the pounds. The climate is not necessarily helped by cutting the big trees and relying on seedlings and saplings to compensate for the loss of the former, carbon sequestration-wise.

We'll see where this all goes, but I've long wanted to see our collective efforts count for more than the individual pleasure we get from our measuring skills. Nothing wrong with that, but I think we can go further. Always have.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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