Sten Light and Survey

[barcelonacvr]

I have heard many people give conflicting responses regarding whether a Stenlight will throw off a survey or not.

Do you survey with the light on or away from your instruments?

I think it is a no brainer seeing as there is a magnetic switch ,however in testing I saw little deviation( my Sten is mounted above my Apex ,maybe the distance is enough?)

A VERY experienced surveyor worked with me on testing this past weekend and he got large deviation right away.


What is the common experience?

[Chris Chenier]

I'm the one who did the test mentioned above. In case you wonder, let me explain how the test was done.

I put the compass (a Suunto sighting compass) on the edge of my wooden kitchen table (and away from any metal), so that I could look into the eyepiece without touching it, and I took a reading. Then I put the helmet on my head (the one with the Apex and Stenlight above it) and took another reading. I did not make deliberate efforts to get the Stenlight particularly close to the compass, nor did I try to keep it far: I was just trying to get a reading much like I would in a cave. Depending on the tilt on my head, I could easily get 2 degrees off the original reading. Just to make sure that the compass had not moved, I took the helmet off and took another reading. It had returned to withing 0.25 degrees of my original reading. (A small tap on the table got it to return to the original reading... the friction on the pivot was too much to get it to turn on its own.) I repeated the process described above 3 more times, getting the same results each time.

If you try this test, remember that the effect on the compass might not be seen, depending on the direction in which the compass is pointing. This is because any metal (or magnet) interfering will pull the north end of the compass towards or away from it. If this happens to be the same direction as magnetic north, then it won't make any difference! For my test, I happened to be looking west.

During the test, the Apex was turned off, but the Stenlight was turned on (to its lowest setting)... just in case the (small) magnetic field caused by the flow of electricity would make a difference. I really wanted to simulate a realistic situation.

Now, this test does not prove that the Stenlight is the culprit here, as the Apex was closer to the compass, but given that both lights were permanently mounded on the helmet (a Petzl Ecrin Roc if I recall), I didn't have much choice.

I understand that having a magnetic switch makes for a good separation between the inside of the lamp and the outside world, but this is not a good idea for surveying! Having a switch (on the "outside") that is eventually replaceable by the end-user should it ever die would have been a much better idea.

I must admit that before that test I was seriously considering buying a Stenlight, but I an now looking elsewhere. Too bad because the size of the Stenlight made it more interesting than its competitors.

Another user of the Stenlight had previously told me that he always took his helmet off when reading instruments (I presume that's done to shine light on the instrument). Might be ok in an horizontal cave, but I won't be doing this in the middle of a deep pit, or whenever there are people above me who could be knocking down rocks... did you ever try to get a good compass reading while receiving rocks on your head?

The search for the perfect light continues... but in the meantime I'd be interested in hearing others' opinion on this.

[Scott McCrea]

I had this concern when the Sten first came out. It's also one of the reasons I don't own one yet. Like you said, the search for the perfect light continues. But, the Sten is as close to perfect as I have seen thus far. A few simple mods would make it much better.

A buddy who surveys with a Sten, simply pops the light out of the mount and slings it over the back of the helmet when he's shooting compass.

If the cord had a coiled section (like a phone cord), you could pull the Sten out of the mount and away from the compass and still use it to light the instrument while leaving the helmet on.

A partial redesign that would allow for attaching a head strap would be nice too. And, I agree with the external switch idea.

The bad thing about lights is the components/technology changes so fast. As soon as you get a good one, a better battery or LED or something comes along.

Almost makes me long for the days when carbide was the only option. Almost.

[barcelonacvr]

Christian:

Thanks again for sharing some of your survey knowledge.Everyone in attendance had a lot of fun and learned a LOT!

Kudos to you/Nibelungens and the SQS.

I will detach my Sten for survey( Thanks for the good idea Scott) as you showed me how much deviation it created,I was curious as to whether some had a trick they might have used to get around this.Most definitely when I held my head flat there was no problem but any deviation from that position threw the readings off.

I am not afraid to ask a dumb question in hopes an inversely intelligent solution might be out there,looks like this time there is not.The Sten is a brilliant light in any manner,can't have everything.

[steelwool]

The Sten does throw off compasses just like most electric lamps. All electric lamps through off compasses to a degree. I just take my sten light off the mount and move it about 8-10 inches away from the compass. At this distance the stenlight doesn't throw a sunntos tandom. I usually use the sten light to light up the compass.

[rchrds]

Almost makes me long for the days when carbide was the only option. Almost.

hehe. I usually sketch, so I had not noticed the issue with the magnetic field caused by my sten, but last week I finished off a survey with a two man team and noticed the effect. No problem. Since my sten is only my backup light- Off it went into the waterproof jug, and continued to use the old standby- CARBIDE!

haha. you electric folks kill me.

Jason

[Jeff Bartlett]

Nice job trying to turn this thread into a stupid fight about carbide. I suspect most people who've purchased a $300 lamp haven't relegated it to backup status.

After I bought my Sten, we did some extensive testing on magnetic deflection with it and other headlamps in order to put together an article for an upcoming LRG newsletter. We tested each headlamp at 1.0', 0.5', 0.25', and 0.1' above a Suunto tandem while photographing through the eyepiece with a zoom lens. The result? The Sten had a noticeable effect (less than a degree) at a distance of 0.5', and by the time it got to 0.1' it was throwing off the compass by 10 degrees or more. This was repeated with the light off, and the light level had no effect on the deflection.

I take my helmet off when I shoot. Or I keep book. =)

[steelwool]

I used to use carbide as a backup with my sten, but my lamp was getting really beat up in my pack... I switched to candles for a heat source instead.

[Crockett]

Sten or NoSten the instrument reader must gear up in a different way.

Most batteries being used by cavers today have an observable effect on the compasses being used. Many of them are helmet mounted less than 1' from the instrument reader's eye. Simply removing the headlamp from a blade and holding it away may not be enough if the batteries are a few inches behind the eye.

Jewelry, including watches (many of them have batteries), should also be avoided by an instrument reader. Some cavers have a habit of wearing something around their neck on a lanyard like a key or a backup light. Pack strap buckles and the contents of pockets must be considered. These things can get too close. Many eye glass frames are not a problem but could be. The potential exists for any object to effect a compass in a meaningful way including in some rare cases the caver or the cave.

It has been pointed out that testing probably will not be enough to reveal an objects effect on a compass since it would require simultaneously rotating objects while measuring. An actual cave survey becomes the test.

I think the best strategy for the instrument reader is to strip down and keep away as much as possible then take a bunch of readings and hope it works. Going without a helmet while doing this is probably not a good idea. This may not sound practical and the tendency is to target the major offenders, like electric lights, and Sten lights in particular it seems, but to get a good efficient survey you need to recognize the big stuff and sweat the small stuff too.

Carbide is simply a mess and does not belong in most caves. The ongoing impact of regular use of a carbide light in a cave is high. The potential for greater impact includes burning the ceiling (and what lives on the ceiling) or spilling the waste or fuel during refueling. Arguments for the use of carbide are usually for the convenience of the caver and do not mitigate the impact. Consider the situation of taking a carbide light into a school, hospital, church, or office. It would probably be considered a nuisance and hazard in these environments. If you replace the carbide light with electric then it is maybe just weird.

If you have read this far and you thought about going into public buildings with a carbide lamp then add this to the image: you stroll over into a corner of a room of the school, hospital, church, or office, look around to make sure nobody is watching, then you urinate on the floor.

Of course if you go over into a corner to pee into a container while nobody is looking you are maybe just weird, again. (Those of you thinking about peeing into your carbide lamp are beyond weird and I don't want to hear about the wonders of it.)

I'm not saying caves are like schools, hospitals, church or office buildings. They are much better.

[NZcaver]

Without getting into the whole carbide argument, remember that most electric cavers use a primary headlamp where the batteries are mounted on the back of the helmet away from any compass readings. Perhaps some smaller self-contained backup headlamps could potentially cause a problem, though? Also, doesn't the Stenlight have a magnetic switch in the light head, or am I confusing that with another headlamp?

Regarding watch batteries, I always wear a plastic-case digital watch on my left wrist while caving. I don't think I've ever removed it specifically to shoot bearings before, although I normally hold my compass/clino in my right hand so I shouldn't be an issue anyway. Some quick informal testing seems to suggest my watch has no deflection effect even when close to the compass, but others may have a different experience.

Some of the Suunto compass models (not mine) have built-in lighting, which might be another option for cavers to consider. Or one could tape (or hold) a tiny 2 inch plastic chemical lightstick to the instrument, as I have seen others do.

[Jeff Bartlett]

In fairly thorough testing, the results of which will be published in an upcoming issue of Arkansas Underground, headlamps with batteries in the back (PT Apex, Petzl Myo XP) effected compass readings SIGNIFICANTLY less than headlamps with the batteries in the front (Petzl Tikka XP) or headlamps with enormous magnets in the headpiece (Stenlight). In fact, certain headlamps like the old Petzl Zoom and Mega didn't shift the compass even with the light ON, and laying on top of the Suunto's compass face.

offhand, I'd say you can keep an Apex (or comparable) on your helmet, provided it is OFF and not at the absolute brim of your helmet (I locate mine ABOVE of my blade mount), and read instruments without any negative effect.

but of course, even when we publish our tests, I expect everyone to laugh and say "you didn't test ____ or ____ which is what I use"... or "you didn't rotate the headlamp during testing" or "you didn't rotate the compass during testing"... insert your own questions here. we have no premonitions of actually changing cavers' minds!

[barcelonacvr]

thank you for all the great posts and information.it is nice to gain more knowledge and ponder different viewpoints.this is what makes the forum an asset.

[Dan Henry]

I use my sten and sketch a lot with it, but when I have to read instruments, I swap my sten for my second, a Petzl Myo XP, which I added a plastic lamp bracket to by cutting an approptiately shaped peice out of a bucket lid. I swap the sten battery for the Myo battery case (held in place with a small webbing strap) and just swap the lamps in the bracket. The myo has a coiled cord so you can read compass and clino without having to take your helmet off for every shot (inefficient at best), and the myo doesn't have a magnetic switch. Also you just use it with the diffuser, and you don't have to worry much about aiming the light into the compass window as it's a pretty broad beam. In this case the Sten becomes my second, but at the end of surveying when we're packing up the survey gear, I swap the Myo back to second status and put the REAL light back on. I have to say that if the Sten had a coiled cord, I think you could hold it far enough away to prevent magnetic errors. In case you messed up and got it too close, it would get caught by the backsights, right?

Dan Henry
Asheville, NC

[FiddleCaver]

"you didn't rotate the compass during testing"

Jeff, I personally don't think that rotating the compass would produce any scientific results other than measuring whatever negligible deviation can be produced by systematic error inherent to the instrument itself. However, I am a bit curious what direction the instrument was facing when you guys tested it. Not to be critical or anything but it seems to me that positioning the instrument so that the reader is facing East or West would optimize the deviation (if there is any measurable...). That way our planet isn't canceling out or directly adding to the effect of the lamp. See you this weekend I hope .