Help with range finding reticule (1 Viewer)

Westie · May 12, 2010

Hi

I was wondering if someone could help me with my binoculars - see attached pics.

These used to belong to my Dad, and are now mine.
I have no idea how to use the range finding reticule. I've been told it can determine the size of an object if the range is known, and the range if the size of the object is known.

Can anyone explain how I use the horizontal and vertical scales, or provide a link to where I can find info on it?
I shoot rifles with scopes, and am familiar with the mil-dot system, but this looks far more complex than that.

The binoculars were bought new in the mid 80s. They are Pentax 7 x 50 (7.1 field) marine binoculars.

Thanks

Matt

Surveyor · May 12, 2010

Westie said:
Hi

I was wondering if someone could help me with my binoculars - see attached pics.

These used to belong to my Dad, and are now mine.
I have no idea how to use the range finding reticule. I've been told it can determine the size of an object if the range is known, and the range if the size of the object is known.

Can anyone explain how I use the horizontal and vertical scales, or provide a link to where I can find info on it?
I shoot rifles with scopes, and am familiar with the mil-dot system, but this looks far more complex than that.

The binoculars were bought new in the mid 80s. They are Pentax 7 x 50 (7.1 field) marine binoculars.

Thanks

Matt

Hi Matt,

If you can, take a picture through the bino of two rulers, one vertical and one horizontal at a known distance.

The horizontal scale appears to be linear, about 10 millirad(or mils) per division (.01 radian/div. or 0.1 radian for the 10 divs.)

The vertical scale appears to be a cosine scale, probably to be read against a known size. Can probably figure it out with a sample.

If this gets too involved, I will PM you my email address and help you figure it out.

A mil is a ratio of 1:1000. If a division is 10 mils, the ratio would be 10:1000 or 1:100. If this is the case and a 1 meter object filled one division, then it would be 100 meters from the bino.

Kevin Purcell · May 12, 2010

The overview on Stadiametric rangefinding is here

http://en.wikipedia.org/wiki/Stadiametric_rangefinding

But these are a little different from the usual military rangefinding marks. Perhaps there is a standard rangefinder style for nautical use?

One shortcut assuming the drawing, which looks like a mechanical drawing is accurate is to make measurement from that. You know the field is 7.1 degrees. So you can scale that to each of the marking and so get the values for the horizontal and vertical scales (and the hash marks).

From Google Calculator 7.1 degrees = 0.123918377 radians or about 124 milliradians ("mils").

So from screen measurements:

The horizontal scale seems to be 10 mils per divison. A nice round number.

The vertical scale is non-linear. Ballistic scale? Seems odd for nautical bins.

The hash marks are about 0.6 mils apart.

Surveyor · May 13, 2010

Matt, without some pictures or actual measurements to compare to, this is just advanced guesswork.

The horizontal bar scale has already been discussed as being 10 mil divisions. It also appears to be about 1 degree below the optical axis.

My guess is the hash-marks are spaced about 20 arc minutes or 1/3 of a degree, a fairly standard marking.

The vertical scale is a mystery to me, never seen anything quiet like it before. Cosine scales are usually associated with circular scales/measurements or tilt indications. This one is odd, also, because, if it is indicating 20 degrees, it would have to be related to the AFOV and not the true FOV (7.1*). The top of the vertical scale may be about 3 degrees above the horizontal scale or 2 degrees above the optical axis.

I will do a little looking and see if I can find something on these scale types. I do not think it would be standard marine unless there is a standard lighthouse height that I am not aware of. Most marine applications refer to the horizon.

Not much help so far.

Best

Kevin Purcell · May 13, 2010

The hash marks are about 0.6 mils apart.

Doh! I put the decimal point in the wrong place (clearly, as they're about half the 10 mil division size). So that should be 6 mils (i.e. 1/3 degree as Ron says).

Surveyor · May 14, 2010

Matt,

I tried emailing tech support at Pentax USA and got the following reply. You may try emailing Japan Tech Support.

Ron,

Thank you for your reply and image samples.

This ASAHI PENTAX 7x50 ranging binocular was never made available to the US market. (We might assume it was only made available in Japan or to the Southeast Asian market).

Unfortunately, we do not have information on the use of the ranging reticle in it. It is certain that this model was produced in the 1970’s before “Honeywell PENTAX” was established in the US.

We do currently produce the waterproof 7x50 PENTAX MARINE binocular with a ranging reticle which is featured in our webstore at: http://www.pentaxwebstore.com/products/sport_optics/binoculars

If you have further questions, please feel free to reply.

Thanks again,

Joe Virgil Product Specialist

A little more looking leads me to believe the vertical scale may be for marine mammel surveys. I have not read or researched the articles but looks as if a scale of this type may be used for adjusting distance or latitude of objects from the horizon.

http://books.google.com/books?id=9-...snum=10&ved=0CD8Q6AEwCTgo#v=onepage&q&f=false

http://www3.interscience.wiley.com/journal/119942772/abstract?CRETRY=1&SRETRY=0

Pinewood · May 14, 2010

Hello,

The reticle is pretty close to the one on US Army binoculars, like my M13A1. The vertical scale is a ballistic scale for infantrymen but I do not recall how it works, except it allows for shooting at something while aiming at another target, at a different range.

Happy bird watching,
Arthur Pinewood

Surveyor · May 14, 2010

Pinewood said:
Hello,

The reticle is pretty close to the one on US Army binoculars, like my M13A1. The vertical scale is a ballistic scale for infantrymen but I do not recall how it works, except it allows for shooting at something while aiming at another target, at a different range.

Happy bird watching,
Arthur Pinewood

Thanks Arthur, that appears to be it.

http://www.twpt.com.tw/eng/showroom/BINOCULAR-M13.html

Now, if Matt can find a M13A1 manual to download.

Kevin Purcell · May 14, 2010

Or a manual for the M3 ... that Taiwanese web page says:

These binoculars are used for observation and have a reticle in the left eyepiece identical to that of BINOCULAR：M3, for approximate measurement of small angles

So a quick edit of the URL

http://www.twpt.com.tw/eng/showroom/BINOCULAR-M3.html

gives the M3 web page (for a 6x30 bin) has some more details:

The binocular M3 contains a reticle in the left eyepiece, for approximate measurement of small angles. The horizontal scale is graduated 10-mil interval from 0 to 50 on both sides of the center of the field of view and marked 1. 2. 3. 4. 5. Above the horizontal scale are two series of graduations, each graduation being spaced 5 mils apart. The vertical scale（range）is graduated in hundreds of yards from 0 to 2,000. When the center vertical line of the mil scale on the reticle is alined with the target, deflection to the right or left of the target can be read on the mil scale.

Pinewood · May 14, 2010

Hello,

I am recalling more. If an officer, with a binocular, sights a target, a sniper or forward observer, obscured by tall grass, at 2000 yards, he puts the target on 20 of the vertical line. If he should see a prominent point, a fence post, above the target at 12, he instructs his riflemen to aim at the fence poste, with their rifle sights set at 1200 yards.

Happy observing,
Arthur Pinewood

Westie · May 15, 2010

Thanks for your help everyone. I have a much better understanding of the scales now.
The reticule looks identical to the one in the link posted by Kevin Purcell.

http://www.twpt.com.tw/eng/showroom/BINOCULAR-M3.html

They were originally purchased in Hong Kong around '85-'86.

clschmalz · Jun 30, 2010

Pentax's comment about 7x50 ranging binoculars not being distributed in US is interesting. I have a pair of 6x30 Asahi Pentax IF complete with the reticule which I purchased last year in San Francisco. They were new (very) old stock in a small shop half a block from Fisherman's Wharf. Other than size they appear identical to Westie's 7x50s.

BigSteve57 · May 2, 2012

I came across this old thread and thought I would reply.

I have a pair of Steiner 7x50 Military-Marine binoculars with the exact same reticle which I bought in the mid 80's. They're incredibly bright and clear and just wonderful for viewing wildlife. They're so bright I've even used them very successfully in moonlight!!!

This reticle was found on the old Army M3 binoculars and the reticle itself is referred to as the M17 reticle.

The reticle is used for the rapid establishment of alternate aiming points for rifle and artillery. The full explanation is found on pages 4-6 of War Department technical manual TM 9-575 AUXILIARY FIRE-CONTROL INSTRUMENTS (FIELD GLASSES, EYEGLASSES, TELESCOPES AND WATCHES) and dated May 4, 1942.

Below is a picture taken from that publication, it is uncopyrighted.

For example: Your target is known to be at 900 yards so you place the 9 on the scale over the target. If your rifle/artillery is zeroed at 500 yards then aim at the top of the hill as shown. If it is zeroed at 1800 yards then aim at the fence as shown. The example is in yards, however this would work for any measure like meters etc...

I'm not sure how this type of scale could apply to bird watching or photography but I hope this information helps someone nonetheless.

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