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01-30-2016, 06:18 AM   #1
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Pentax 8x30/6.2 Monocular

I would like to figure out how to use it. Can't find instructions anywhere.
It has a 4-division reticle inside with each division having 10 divisions.
It appears that these may represent angles, with the outside edges being the full 6.2 degrees. But I could be wrong on that.

For a right triangle where the base length is known and a second angle is known, what is the formula for calculating the height.
I'd like to figure out how to use the reticle in that monocular. Can't find instructions anywhere.
Though I did find a user who spoke very highly of it.
This monocular thing
One nifty gizmo.

01-30-2016, 07:42 AM   #2
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Moved to proper area.
01-30-2016, 10:47 AM   #3
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There are some formulas here.

6.2 degrees correspond roughly to 8x magnification so that seems right. The angle measuring device is called an Inclinometer and can be used to calculate distance if you know the height of the measured object.
02-01-2016, 11:50 PM   #4
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SOACOATOA - search on it.

https://www.google.com/search?q=sohcahtoa&tbm=isch&tbo=u&source=univ&sa=X&ve...w=1142&bih=639

02-23-2016, 03:50 AM   #5
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I was looking for a decent monocular and a lot of the cheaper brands had fairly terrible reviews, except for some items by Bushnell and ATN. Their image quality and brightness seem to be very close to my early-90's Pentax 8x40 roof prism binos, which are all glass, fully coated and heavy. I know Pentax is known for great optics that don't break the bank, so I might want to take a chance based on Pentax's reputation alone.
02-26-2016, 12:28 PM   #6
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the people who do this for a living used to be timber cruisers

they would survey timber acreages for density and quality of trees for lumber

you should be able to google (use the free books option) "timber cruising" "cruising" "timber survey" and find the methodology for your prize
if I recall correctly the books may very well contain tables that reduce your need for a calculator

one the simpler functions of the inclinometer is to shoot the rise of a grade

on shorter trees than those native specimen hunters are calculating you use a protractor and a yardstick

stand back a known distance
set the base level to your eye
rotate the yardstick (beam) to top of the tree

with length of your base and the angle you shot you can calculate the rest of the triangle using trig or geometry (which I detested in my youth and have since wished i'd cared more for)

timber worker suppliers even sell a special nail to hold your tape when you establish your base measurement
now of course there are reasonably accurate consumer lasers that can reduce your tick exposure (you did notice on their home page the tucked khaki trousers)

I've used the stick , tape and protractor method a couple of times on known objects
it is fairly accurate
close enough for government work anyway

the only downside to using your tool as a monocular is that it likely is not close focusing
however most of those tools are still optically superior

have fun!

---------- Post added 02-26-16 at 01:36 PM ----------

QuoteOriginally posted by thattee Quote
I was looking for a decent monocular and a lot of the cheaper brands had fairly terrible reviews, except for some items by Bushnell and ATN. Their image quality and brightness seem to be very close to my early-90's Pentax 8x40 roof prism binos, which are all glass, fully coated and heavy. I know Pentax is known for great optics that don't break the bank, so I might want to take a chance based on Pentax's reputation alone.
if you're really looking you might try vortex
I have really been surprised at their quality and durability
the optics are crisp and sharp
even the least expensive models are good

the tactical monocular they make is a little over the top
11-07-2019, 06:09 PM - 1 Like   #7
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QuoteOriginally posted by Collinb Quote
I would like to figure out how to use it. Can't find instructions anywhere.
It has a 4-division reticle inside with each division having 10 divisions.
It appears that these may represent angles, with the outside edges being the full 6.2 degrees. But I could be wrong on that.
I have one of these. It is designed to be both a monocular telescope (for distant things) and a low-power microscope (for viewing small things). There are two optical pieces: the monocular itself, and a clear plastic stand which contains a lens and a focusing ring.

To use it as a monocular, you simply look through it like any monocular, ignoring the measuring reticle. The eyepiece focuser allows you to focus on whatever distant object you are looking at. In this mode, it is 8 X magnification and has a 6.2 degree field of view.

To use it as a microscope, you screw the threads on the upper end of the stand into the front end of the monocular, forming a single longer unit. While looking through the eyepiece, you adjust the eyepiece focuser to make the reticle sharp. Then you place the plastic stand on something flat (e.g. a piece of paper with printing on it, a slide mount with film in it, etc.) and use the focusing ring on the stand to bring the object under the stand into focus. In this mode, the magnification is about 25 X, comparable to mid-power on a stereo microscope.

The reticle is intended for use in microscope mode. It can be used to measure the size of objects under the microscope in mm. The reticle covers 4 mm in 0.1 mm steps. Try putting the microscope on top of a metric ruler and see how accurate the graduations are. On mine, they are very accurate.

Although the reticle was intended to measure distances in microscope mode, it can also be used to measure angles in monocular/telescope mode. (The lens in the stand creates a virtual image of the object being examined at infinity, effectively converting distances on the object into angular separation in the image. Then the monocular focuses on this virtual image and converts angular distance back into linear distance on the reticle.) To use the reticle to measure angles, you just need to know what the reticle scale means in angular terms.

By calculation: I assumed that the overall magnification of the devices in microscope mode is 25 X. Then the magnification of the lens in the base is 25/8 = 3.125 X. This means the lens focal length is 250/3.125 = 80 mm. A 1 mm distance on the microscope's subject becomes an angle difference of 1/80 = 0.0125 radians when placed at the focus of an 80 mm lens. So, 1 mm distance on the reticle scale (10 divisions) represents an angle of 12.5 milliradians. (If you aren't familiar with milliradians, one milliradian is the angular size of a 1 foot long object viewed from 1000 feet, or a 1 mm long object viewed from 1 m).

Then I tried measuring the size of a door in my house using the monocular reticle, and measuring its width and distance directly with a laser distance measurer. Using this method, I calculated a scale factor of 12.7 milliradians per mm on the reticle. That's close enough to 12.5 mrad/mm to be nothing more than experimental error. So I think 12.5 mrad/mm is a good value to use when measuring angles.

An example of how you might use this: You sight a tree some distance away, and measure its trunk diameter as 2 mm on the reticle. That is an angle of 12.5 x 2 = 25 milliradians. This means that the diameter of the real object is 25/1000 of the distance to the real object. If the tree is 10 m away (10000 mm), then its trunk diameter is 250 mm. On the other hand, if the tree is 40 m away, the trunk is 1 m in diameter.

Similarly, if you know the size of something (a human standing up, a golf hole flag, etc) and you measure its angular size in milliradians, you can calculate how far away from it you are.

- Dave

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