One reason people don't return the signal mirrors with non-functional aiming mesh that Doug Ritter describes in his article (Click this link to read the article: Phony Signal Mirrors ) is that people who've never used a mirror with a retroreflective aimer mesh don't know what to expect.

They mistake the reflected light from the mirror for the "bright light spot" "aim indicator" described in the instructions on the back of the mirror.

If you've never used such a mirror (or want to describe it to someone who hasn't) click on this link: Photo of view through aimer.

The three photos there are large, with detailed descriptions - this post has only short captions and thumbnails.

(1) The view of the reflected mirror light on your hand:
(2) The view through the aimer:
(3) The view of the "fireball" against the sky (that's not the sun)



Similar photos are in my handy printable instruction sheet:
http://www.equipped.org/pp/pic2042.htm

Doug Ritter's illustrated instructions are here:
http://www.equipped.org/psp/psp_rescueflash.htm

Thanks for the info. I understand how to use a mirror with a retroreflective aimer, but can you explain how this type of aimer works (optically)? It seems that for you to see the "fireball" in the retroreflective material, the source of the light would have to be between the back of the mirror and your eyeball...

The "fireball" you see is mainly an internal reflection off the inside face of the glass that faces the sun. I've illustrated the process at below right, and explained the process in the text on the figure. ( The figure below is small - the large version is in Doug's article here: http://www.equipped.org/phony_signal_mirrors.htm )

In general, there are actually two superimposed "fireballs". One is an internal reflection from the inside face of the glass face that faces the sun, and the second is an internal reflection from the inside face of the glass face facing the user.

The path illustrated below is the one arising from the internal reflection off the inside face of the glass surface facing the sun. This path exists for both solid retroreflective aimers (like the StarFlash) and mesh aimers. The path of the light creating this "fireball" traverses in the following sequence:

(a) Sunlight passes from the sun directly through the glass and hits the retroreflective beads
(b) The beads reflect the light directly towards the sun, back through the glass.
(c) The glass reflects a small fraction of the light internally, at the inside face of the glass-air interface facing the sun. This light, which was headed towards the sun, never exits the glass on the sunny side, but is reflected towards your eye, instead.
(d) The direction of the light in (c) is exactly opposite the main reflection of the mirror, so it seems to you to originate from the same direction you are reflecting the light.



There's a similar path for the retroreflective surface facing your eye. In a way, I think it is easier to understand than the first, but since many mirrors only put retroreflective material on the side facing away from you, I illustrated that one. I've also omitted the effect of refraction, since the effect works the same way with or without it, and it simply adds confusion.

Here are some patent diagrams, which include the light bending effect of refraction, but show what's going on inside the mirror in larger scale:

(1) Link to: Solid Retroreflector aimer Diagram (like StarFlash)
(2) Link to: Mesh aimer diagram (showing paths off front and back of mesh)

Thanks for the explanation! I hadn't thought about the internal reflection.

I find that my vintage mirror with the + shaped aiming hole and mirrored back is very accurate. However, it does take some practice and coordination. Not something you want to try for the first time when you really need it.

You're welcome.

Yes, the WWII General Electric ESM/1 & ESM/2 "cross in glass" mirrors using the rearsight method are quite accurate, but there is more coordination involved. US Coast Guard testing found that subjects hit the plane more than twice as often with retroreflective aimers that with the "cross-in-glass" style when bobbing in a small liferaft/dinghy. I expect the difference would reduce on solid ground.

Here's a few links along those lines:
Illustrated instructions for aiming double-faced signal mirrors
Specific Instructions for GE "cross-in-glass" mirrors
Four examples of the ESM/1 4"x5" "cross-in-glass" mirrors
Two examples of the ESM/2 3"x5" "cross-in-glass" mirrors

Yes, trying to use a signal mirror for the first time when you need it is not a great idea.

The US Coast Guard, which requires all personnel to carry signal mirrors when afloat,
makes a point of testing their members on that skill.

Here's a nicely illustrated USCG PowerPoint signal mirror training package
http://www.completepqs.com/assets/files/bcm/ppt/BCM-02-09.ppt
It's on this USCG training site, with lots of related topics:
http://www.completepqs.com/index.php?id=57

If I recall correctly: The best & quickest way of determing if a signal mirror is the real MaCoy & not an cheap knock off (without removing it from it's bubble packaging)is to photograph it using the flash on your camera. You should see a hotspot over the retro reflective grid.

If you don't it's a knock off. Avoid.

That method works well, and Doug uses it effectively in his article. It's also a great way to show someone else why you think there is an issue with an aimer, especially with "side by side" photos next to a good aimer.

There are three good alternatives, though:

(1) Buy a mirror with a reputable brand.
(2) Test for retroreflectivity with a flashlight
(3) Buy it, try using it in the sun and return it if it is defective.

In more detail:

(1) Buy a mirror with a reputable brand.

The glass mirrors with mesh aimers that are branded:

• Coghlans
• S.I. Howard Glass
• Vector 1
• Rescue Reflectors

should work - I have at least three from each source, and no complaints.

Glass mirrors with apparent mesh aimers that aren't one of the above, I'd test.


Doug's article lists distributors from whom he has received glass signal mirrors with dysfunctional mesh aimers, and lists what he finds to be "readily identifiable marks" of the fake mirrors.

I've only ever had one plastic signal mirror whose mesh didn't seem retroreflective (and it was the brand Doug mentions in his article), so it's much less of a problem for plastic mirrors. Decent plastic mirrors with retroreflective mesh/meshlike aimers are:

• The 2"x3" Rescue Flash mirror from American Medical Kits
• The various sized mirrors from Rescue Reflectors
• The "Sight-Grid" buoyant signal mirror from Coghlan's / Vector 1
• The 3"x5" ACR "Hot Shot" mirror
• The "Bright Spot" Scubapro Diver's Mirror from ASTI

Note that there are are also several good signal mirrors with decent solid retroreflective aimers - the StarFlash buoyant mirrors, in particular.

(2) Test for retroreflectivity with a flashlight

This is a handy way to test bubble-packed mirrors for those (like me) with a small "everyday carry" flashlight on their key chain. Hold the flashlight tight against your temple (right next to one eye) and hold the package with the mirror aimer about 9 inches in front of your nose, with the mesh illuminated by the flashlight. The mesh should look significantly brighter to the eye adjacent to the flashlight than the other. The difference is striking on most modern mirrors with retroreflective aimers, but much more subtle on pre-1980 Mil-M-18371 government issue mirrors, especially if there is a light background (e.g., white paper) behind them. With a black background, though, even such mirrors exhibit this clearly. If you are at home (e.g., the mirror came mail-order), this test works even better in darkness.

The camera flash method does work well for the pre-1980 mirrors - the top photo below of a 1968 MIL-M-18371 mirror was apparently take with flash,
and the lower one without:
http://www.modernforces.com/uniform_mirror.htm


(3) Buy it, try using it in the sun and return it if it is defective.

I've bought mirrors from many sources where the mesh didn't exhibit retroreflectivity, and I've never had any difficulty returning them.