MLU FORUM - Cotton type rangefinder

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Cotton type rangefinder

I guess it could have military and civilian applications.

http://www.dehilster.info/index.php?...der/index.html

Thanks for the link Graeme

It's a beautifully crafted instrument which my dad bought because he appreciated these sorts of things as I do. We discovered it while clearing my mother's house.

Keith,

What do you think it was used for? Requiring a known height indicates it is some sort of surveying instrument but 20 feet being the smallest setting - a pretty high pole!

It seems far too accurate and unflexible to be getting distances from guessed object heights so seems to have little field application.

Lang

Bit of a mystery still

Quote:

Originally Posted by Lang (Post 153903)

Have had more of a snoop around the internet and there is one in the Opticalia museum link
It has been shown on one site as having something to do with the military, but it would seem to have more of an application in the surveying field.
The company who made it, E.R. Watts made all sorts of interesting optical things including bomb aiming instruments during the second world war.

It would appear to have nautical connections according to this:

Link

Quote:

Instrument : Range Finder Cotton Type MKII
Manufacturer : E.R. Watts & Son. London.
Country of origin : U.K.
Manufacturing year : Early 20th century
Like the stadimeter this instrument was used to measure the distance of an object from the observer.

A 4" long linear concave lens (in cross section front and rear of the glass are parallel) is fixed to the base. A prism is mounted on a carriage with an index mark that slides back and forth along the axis of the instrument. When at infinity the slanted side of the prism is parallel to the corresponding part of the concave lens and cancels out any light breaking. A distance to an object can be measured when the height (or width) of the object is known. The carriage is slid until both ends of the object coincide, similar to the use of a stadimeter or sextant.

Three reversible brass inserts calibrated on both sides in distance in yards, corresponding to various base heights, (20 and 25 feet, 30 and 35 feet and 40 and 50 feet), are fitted along the axis of the instrument. When the scale for the appropriate base height is selected and inserted, the carriage can be slid for coincidence and the distance read at the index mark on the sliding carriage.

Keith,

Very interesting. I suppose you could turn it on its side to measure the distance to another ship, because they knew the exact length - even enemy ships - but it does not seem to go high enough in the numbers. Maybe fighter pilots used it because they knew the wingspan of the enemy aircraft. Just hold the throttle in the left hand, the stick in the right hand and the rangefinder in the other hand.

Watts is still running, they make electronic navigation equipment now. A lot of our army prismatic compasses were made by Watts.

Lang

It appears to be related to the Stadimeter which was used by ships in convoy to keep their appropriate distances.

The sliding scale is one of several differently calibrated carried within the instrument.

We learn something every day...