User Review: Cammenga Lensatic Compass
Source: bought it new
Price Paid: $50
Well-made, but less than ideal for non-military users.
- Air-filled compass housing can't develop a bubble
- Self-luminous tritium lighting (in some models)
- Excellent manufacturing and assembly quality
- Deep-well compass housing for use in multiple magnetic zones
- Mediocre accuracy
- Mediocre shock resistance
- No protractor base for taking bearings from a map
- Degree scale in 5-degree increments only
- Can fog over in certain conditions
- Floating compass dial slow to settle
The U.S. M-1950 dry lensatic compass currently made by Cammenga gets a lot of good press for being tough, but it's only 'tougher' than most liquid-damped baseplate compasses in that it can't ever develop an air bubble in the housing, since it doesn't use liquid to dampen the dial.
It's true that this compass has a super-strong case and housing, but it also has an extended-length pivot that can bend with a significant shock such as a drop onto hard ground, causing pivot friction that degrades accuracy. Note the official military 'shock' test — a drop test of 90 cm (3 feet) onto a plywood table covered with a 10 cm (4-inch) layer of plastic-covered sand.
This compass is often praised for its superior accuracy over most baseplate style compass designs in shooting an azimuth (taking a bearing) to an objective or landmark. Let's examine that.
The compass dial is in both mils and degrees, and as the military uses mils, the degree scale is given second place on the dial. As a result, the degree scale is only marked in large five-degree increments — a dial you'd expect on a $10 compass, not one costing $50 or more.
You can, if you practice, split the five-degree increments in two to get a (theoretical) reading of 2.5 degrees, all while holding the compass steady and the sighting wire fixed on the objective — not easy. Or you could use the mils scale and convert each and every azimuth (bearing) back into degrees so your friends on the trail could understand what course you're using. But who's going to bother with that?
I just don't understand why Cammenga doesn't put out a version with the degree scale on the outer edge of the dial in one- or two-degree increments for the benefit of its civilian land navigators.
Then there is the issue of inherent accuracy. Brand-new, the G.I. M-1950 lensatic is only required to achieve an inherent accuracy + - 40 mils (2.25 degrees) from actual azimuth under milspec requirements. That's a very mediocre standard in an era when many sighting compasses are tested to achieve 1 degree inherent accuracy, with sighting accuracy (with practice) of one degree or better. Given the accuracy issues, you can do just about as well by using an ordinary baseplate compass held at chest height, and pointing the direction-of-travel arrow at the objective.
The compass uses magnetic 'induction dampening' instead of the more common liquid dampening used in many baseplate compasses, which is advertised as an advantage (no way to form air bubbles or leak). But what most people don't know is that the original M-1938 U.S. Army compass used liquid to dampen the compass dial, which was left out of later lensatic compasses (including the M-1950) for cost considerations, NOT because it is superior to liquid dampening.
Since it is filled with ordinary air, the M-1950 can and does fog over in cold weather or from moisture and humidity changes in tropical regions, since the interior is not purged with inert gas like your fogproof binoculars or rifle scope. Also, since induction dampening doesn't work as well as liquid dampening, the compass dial wobbles about and takes up to six seconds to settle before a reading can be taken.
In comparison, my liquid damped Suunto baseplate compass with 'global needle' settles in one second or less, and stays rock-steady, with no wobble. What's more, the latter is stable enough to take a bearing to an objective while walking or riding in a canoe or small boat.
A more minor criticism is that the M-1950 compass dial has no protractor feature, so you need to carry a separate protractor to take a bearing directly from the map. It has no romer scales, and only one 1:50,000 metric scale, which isn't much use for USGS 1:24,000 topos. It also has no adjustable declination feature for relating all compass headings to true north. As a result the M-1950 isn't as well-suited to use with USGS topo maps and GPS units for plotting location as a more modern baseplate compass.
The compass itself is built with attention to detail and all parts on my example were well-fitted with no signs of manufacturing or assembly defects. Cammenga does an excellent job on meeting milspec standards.
The tritium sighting is a great option for low light and the occasional emergency night hike, and should be available on other compass models here in the states (outside North America, anyone can buy a Silva of Sweden 4b or 54b Expedition military compass with beta, or tritium lighting). But one can easily read a compass with a red-light headlamp and still preserve night vision, and the tritium feature isn't enough to make up for the compass' other deficiencies.
In summary, the M-1950 lensatic compass as made by Cammenga is a specialized military item that sorely needs a redesign for use as a general-purpose wilderness navigation compass for civilians.