Magnifing lens, compasses and EDC

Everytime I consider a purchase I have to make clear in my mind what it is for, what kit does it belong to, and value for money.
Carrying on with that line of thought I had selected the following products for my EDC:

A compass: http://www.swoptics.co.uk/view.asp?KEY=1935
Whilst I recognise the value of carrying one, it seems to be missing on some EDC's recently posted. Views as to my choice and to why EDC compasses are not often mentioned or reviewed for Type, durability, reliabilty...etc

Magnifying Glass:http://www.swoptics.co.uk/view.asp?KEY=1465
Looks decent to me.. The same company also does len's with a x7 and a x10 magnifcation. Does the magnification strength have any bearing on its fire starting capabilites, or for that matter any other benefit? Does it really belong in an EDC kit?

Thanks for your help

7x and 10x power makes no sense for a magnifying lens. The only proper measures would be either focal length, or diopters. Focal length would specify how far from the tinder you would have to put the lens.

The measurement that's important for starting fires is area. The bigger the lens, the more light it collects, and thus the higher temperature it will get. It doesn't even have to be very optically pure, which makes those thin fresnel lens sheets ideal for firestarting. I got one about 8x10, it will strip paint on a hazy day in the fall in MN. A glass lens of that area would probably weigh a pound or two, the fresnel lens is just an ounce or two.

I just thought about this a little, and my last post wasn't entirely correct. Focal length does matter for firestarting a little bit. A shorter focal length, which would correspond to a higher magnification or a thicker lens (higher diopters) will shine a smaller image of the sun on the tinder. That will make the image hotter. However, total light gather capability is much more important. I had a hard time even making smoke with a credit card sized fresnel lens.

EDC in urban situations doesn't often list a compass.They can be very helpfull if you find yourself in a new city. Sometimes knowing cardinal directions help sort things out. For this purpose your Silva is simple but of excellent quality. If you have, or plan to acquire a compass for outdoor use people usually invest in a more accurate unit with adjustment for declination. this compass will still be valuable for practise and training.

I've used a magnifying glass for first aid a couple of times (small splinters are easier to remove when you actually see them). For most purposes 2 - 4 times magnification is enough. when the magnification is too big the image gets shaky when have a look at something. I carry a fresnel lens as they are small and leightweight. They take almost no space in my wallet. I'd rate it more usefull for urban EDC than compss (which carry anyway).

If you are in a smoke-filled room with almost zero visiblity, is a compass of any help getting oriented?

I suspect not. You won't have a lot of time to faff about, and you can probably just keep going until you hit a wall and then follow the wall without needing a compass. On the other hand, if I was lost in a big building (eg the World Trade Centre) I might be glad of one.

I believe a compass is a "must have item". I have been in urban disasters where the local landmarks have been destroyed and the whole place seems unfamiliar. It is very easy to get disoriented and move the wrong direction. This is not a good idea.

Even in normal life, exiting from an underground train station into an unfamiliar city can be very confusing. I carry a small compass and can easily check my "intuition" and quickly orient myself.

The magnifier on the compass is probably used to read the fine print on some maps. I doubt that it is for fire starting as it is a pretty small diameter.

After a long search, I finally found a Fresnel lens for sale in the uk. At only £0.96 each, as opposed to the £18 quoted for the lens in my link, I think I'll give them a try.
Thanks

hi Goatrider
Thanks for your info.
You carry a 8x10cm(?) on you? I'm surprised you had trouble starting a fire with a cardit card size lens. I remember starting fires in my schooldays with very small Christmas cracker lens. (not a fresnel though, but cheap never the less).
Its sound like the strenghth of the sun ultimatley determines sucess or not - focal length and diopters seem rather irrelevant to fire starting when comparing lens - if I understand you correctly. (correct me if I'm wrong..)

No, I don't EDC an 8x10! I just bought an assortment of them to try out, and that was the biggest.

When I tried starting a fire with the credit card sized fresnel, it was in northern MN, on a slightly hazy day in August. Sun was probably only about 50 degrees high, so it's less light than further south.

Where did you find the Fresnel lens? I found some at MUTR for 29p.

They also have other interesting materials and kit, mostly aimed at teachers. I am trying to decide if I really need a geiger counter. <img src="/images/graemlins/tongue.gif" alt="" />

http://3dlens.com/

Hi
I must have got my pricing wrong in my original post - they were next to nothing, I remember that....Same place though. The only snag being the postage cost ?2.50ish.., so I ordered 5 lens just to make it worthwhile. Even so, the postage still cost twice as much as the lens did. <img src="/images/graemlins/frown.gif" alt="" />
If it wasn't for the direct link to the len's from google, I doubt if I would have found them - I had a hard time navigating back to them - they seemed well hidden....prehaps its just me? <img src="/images/graemlins/blush.gif" alt="" />