Lensatic Compass

[Chambers]

I have always used a normal base plate compass but after a clear out my parents handed my my brothers old lensatic compass he had in scouts. Im just looking into how to use it and am just wondering how many other people know how to use them and what they thing of them

 

[Carbuncle]

You need to use it with one of these, or something similar:
http://www.penrithsurvival.com/penrith_survival/mia/d/silva+protractor/pid/1076310

In your baseplate compass, you effectively have a compass and protractor in one. Using a lensatic compass they're separate. I've used one in the past and found it awfully cumbersome, and a woeful tradoff for a marginal increase in accuracy. But if you want to give it a go, this document, albeit a thinly disguised advert for the US army compasses, and rampant with dubious logic, may be useful.
http://www.cunninghameramblers.org.uk/TW - Lensatic Compass Evaluation.pdf

 

[Chambers]

Just been looking it up, to take a bearing is almost instant, point and shoot as they say but to set a bearing, well thats a bit more tough

Suppose it could be hany to check your bearing whilst travelling quickly i.e. scouts navigating and you just want to quickly check but then again why carry two compasses

Think I will to the baseplate compass

 

[RAPPLEBY2000]

I've used them since i was a kid,
always found them far more accurate than the normal flat type.

sadly most people reject the idea thinking they are old fashioned.

it is difficult to use on a map (where normal compass's fill the gap) .

I have one but haven't used it a few years, same as you.

 

[Chambers]

I would have just thought it a bit of a b@ll @che to have to use the proper protractor sheet whilst out to set a bearing?

 

[Carbuncle]

I would have just thought it a bit of a b@ll @che to have to use the proper protractor sheet whilst out to set a bearing?

That was my experience (though it was about 12 years ago). But I figure the Yank military use them, so either I'm doing something wrong, or the military want something different from their compasses, that sways the tradeoff. There seems to be a few americans on here, so maybe they'd help out, I'd be interested to know.

always found them far more accurate than the normal flat type

Undoutedly. You probably go from Prismatic > Lensatic > Mirror > Basplate-from-the-waist, at least in the types of compasses I've used. But I find the latter to be more than adequate and far more convenient for anything I ever do, and in reality, 90+% of the navigation I do is relating features on the ground to the map, and the only compass involvement is occasionally setting the map. But that's hiking in the UK for you.

 

[hoppinmad]

Hi,
If the compass has a straight edge along the side which some do.. then you can take a bearing by setting the map ie
1 rotate the bessel untill the index line is at the 12 o'clock [north] position
2 align the straight edge of the compass along the north-south grid line
3 rotate map and compass together untill the compass needle is aligned with the index line...the map is now set to magnetic north
4 keeping the map in the same position, align the compass edge along the required bearing ie from your position to the position required
5 read the bearing under the index line..or set it on the compass by rotation the index line over the compass needle

because the bearing that you take is a magnetic bearing, you do not need to correct for variation

I find the above meathod usefull even with a protracter compass if their is a lot of detail on the map which makes the grid lines difficult to see..the main disadvantage is that you have to put the map down on a fairly level surface and keep it still

hope this helps
regards
stu

 

[RAPPLEBY2000]

Undoutedly. You probably go from Prismatic > Lensatic > Mirror > Basplate-from-the-waist, at least in the types of compasses I've used. But I find the latter to be more than adequate and far more convenient for anything I ever do, and in reality, 90+% of the navigation I do is relating features on the ground to the map, and the only compass involvement is occasionally setting the map. But that's hiking in the UK for you.

which is why I used my Silva for mountain leadership training.
I guess when it comes down to it, it's lighter, less bulky, less complicated, less to go wrong etc etc.

 

[johnboy]

A Silva syle baseplate compass is pretty much all you need for 99.99% of navigation on land in the UK. Lenstatic or Prismatic Compasses are really good fun to mess around with but if you're decending in a clagged out hooly off of Corn Du in March you really don't want to be messing around with a seperate protractor...

I'd recommend the Silva Expedition 54 which gives you the best of both worlds base plate simplicity and a sighting prism for accurate bearings.( for doing resection when getting assessed for your ML for example). But I just generally use a cheap and fuss free Silva Field 7.

which is why I used my Silva for mountain leadership training.

Was that Summer ML?

 

[Martyn]

It's true that they (lensatics and prismatics) are more cumbersome with maps, but they are really a marching compass. They are aimed at a slightly different style of navigation. If you are the kind of navigator that refers to a map frequently, then you will find them a bit of a pain in all likelihood. On the other hand, if you prefer to rely more on general navigational skills ...observation, sun, time, landmarks, trees etc ...plus a compass and notepad, then they are a pleasure to use. Lets be honest, how often do you really stop to triangulate on a map anyway? Taking a bearing (on a prismatic) is supremely accurate and very fast. If you want to transfer that accuracy to a map though, it all has to be done longhand. Personally, I can live with having to use a protractor and romer for map work, in exchange for the pleasure of using a prismatic. ...just dont forget grid to mag, add, mag to grid, get rid.

They are certainly not for everyone. If you like the accuracy of the prismatic, but want the ease of map work you get with a baseplate, then the Silva 54 is the one you want. I'll stick with me Franny Barker though.

I did a writeup on the FBM88 which deals with some of the pros and cons of that type of compass....
http://www.britishblades.com/forums/content.php?22-Francis-Barker-M-88-Prismatic-compass-review

 

[johnboy]

work, in exchange for the pleasure of using a prismatic. ...just dont forget grid to mag, add, mag to grid, get rid.

Spoken like someone who is the Northern Hemisphere / Zone 1.....

Down here in Zone 5 it's Grid to Mag get rid, Mag to Grid Add and we do have to add quite a bit of a variation.... about 22 degrees depending on where you are What's the variation in the UK currently... 2 degrees??

 

[Martyn]

Spoken like someone who is the Northern Hemisphere.....

Down here it's Grid to Mag get rid, Mag to Grid Add and we do have to add quite a bit of a variation.... about 22 degrees depending on where you are What's the variation in the UK currently... 2 degrees??

Yep, somewhere between 1.5 to 2.3 degrees or something like that. Very little ...which in truth makes a nonsense of bothering with ...which makes a nonesense of having a prismatic compass that is accurate to a quarter of a degree. But for me anyway, calculating declination is a good habbit to get into. Who knows, I might visit NZ one day and need to do it.

 

[johnboy]

. But for me anyway, calculating declination is a good habbit to get into. Who knows, I might visit NZ one day and need to do it.

Let me know when you're heading on down.. You can borrow my Silva...

 

[Martyn]

I might bring my own.

 

[johnboy]

No Need to you can borrow this old clunker of mine....

 

[Martyn]

Yeah, I'd take that rough old thing off your hands for a beer?

 

[Melonfish]

In a lensatic doesn't the cover fold open flat so you use that as your bearing marker?
then when you have that you flip it up to sight in your course?
or am i being dense? (likely)

 

[johnboy]

Genuine US Issue Lenstatic....

Needs to be used with a Protractor to get the best out of it...

 

[timboggle]

I'd recommend the Silva Expedition 54 which gives you the best of both worlds base plate simplicity and a sighting prism for accurate bearings.( for doing resection when getting assessed for your ML for example). But I just generally use a cheap and fuss free Silva Field 7.


Was that Summer ML?

Mate, if you're doing an ML assessment and using your compass to do resections to know your position in good visibility you'll be laughed off the course dude, at that level you must be able to know where you are by reading the 'map to ground' features, using micro-navigaition, aspect of slope, etc.......... if the 'clag' is down and visibility is bad, what use are compass resections??.

 

[johnboy]

Mate, if you're doing an ML assessment and using your compass to do resections to know your position in good visibility you'll be laughed off the course dude, at that level you must be able to know where you are by reading the 'map to ground' features, using micro-navigaition, aspect of slope, etc.......... if the 'clag' is down and visibility is bad, what use are compass resections??.

I agree 150% they're of little practical 'value' but we had to do em on both my Summer and Winter ML training / assessments (and on my Bush 1 here in NZ where they're of less value as your in the ulu and cannot see chuff all to do a resection on even in good weather!!). It just seemd prudent to do what was asked by the assessor at the time rather than argue over the relative merits of stuff. It was a good while ago though so I'm not up with the currency of the ML syllabus TBH. From memory they're still in the current edition of 'Mountaincraft and Leadership' IIRC...

If you have to do them it makes sense to use a baseplate style compass....

Im not sure what ML is like now under MLTE but you used to hear of all sorts of stuff being asked for or not on assessments.. I think with decent moderation of the assessors it's probably gotten a lot better.