How (non battery operated) do range finding binoculars work? (1 Viewer)

How do range finding binoculars work (non battery operated) ?

This post concerns binoculars that do not use batteries, lasers and other electronic ranging devices.


Some binoculars when viewing, have lines with perpendicular measuring points along the reference line for determining distance. How do these lines indicate distance (if that is what they are for)? Or what are they for?

Thanks in advance
TVC

Hi TVC,
There are a lot of different types out there so may need a pic or better description to get to the right type.

Most of these are some form of fixed angle measurements. One of the more popular is called the mil dot system. There may only be one dot, or a series of graduated dots. If it is one dot of 1 mil (milli radian) then it will subtend a 1:1000 ratio so if it covers a 6' man, he would be 6000' away.

Another type that you find in binos and instruments made for construction or recon work is called stadia wires. They usually have a regular cross hair with a short line about 15' above, below and maybe either side of the center wire. These are usually calibrated to subtend 1;100 so if you look at a level rod or ruler and read 2.45' between these lines the distance would be approx. 245'.

The golf type are usually calibrated to read yards when the flag stick fits between lines.

The kind you describe is the most flexible. Some only have a vertical line with cross marks, some have both vertical and horizontal lines. The cross marks are usually either 5 arc minutes or 0.1 degree.

There are also some binos that just use a calibrated focus knob but in my opinion, these are only useful at very short ranges.

While not binos, there are some types out there that use two lenses with prisms, one of which is rotated to overlap a tinted image (like an old rangefinder camera).

Hope this helps.
Have a good day.

Ron

Ron,

Thank You very much!

This does clear up the basic principal behind these systems for me.


Regards
TVC

Put simply the calibrated line variety rely on you estimating the size of what you are looking at and being proficient at mental arithmetic!

I have a pair of sailing binoculars with vertical & horizontal scales in the viewing area. I also have a circular distance calculator around one of the objective lens barrels. By identifying an object ashore of known height (recorded on the navigational chart), or known width (also from the chart), you can look at the object, measure the number of gradations that correspond to its' height or width and transfer them onto the lens barrel calculator and use it to calculate your "distance off." These binoculars also have an internal compass which you can use to take bearings which enable you to identify your position by taking a "triangular fix" & plotting it on the chart. You can also use the compass bearing on a moving object (if it does not change over time) to identify that you are on a collision course.