The Visual Light part of the EM Spectrum

That would be a gelatinous cube. Not exactly the same thing, though both are vulnerable to fire and acid.

Cubozoans are what are commonly called box jellyfish. They are superficially similar to true jellyfish but the two groups are about as closely related as humans are to eels. The cubozoans are more advanced than jellyfish and are moderately active predators, and they usually possess several imaging eyes to enable them to locate their prey.

It depends a lot on who you ask, and I freely admit my knowledge is about 15 years old so things have probably changed.

Basically there are chelicerates, which have a fairly bizarre embryology and a fairly simple body plan where the mouthparts are essentially just modified legs located at the front of the body. These include the spiders, ticks, mites, horseshoe crabs and so forth.

Then there are the Uniramia. These have the same basic embryology as the annelids and onycophorans but the mouthparts are heavily modified to the point where they no longer resemble limbs at all, and the mouthparts aren’t located on the front head at all, but well back behind the antennae. This group includes the insects, centipedes, millipedes and so forth.

Thirdly there are the Biramia, comprised mainly of crustaceans with a couple of odd side-groups. These show an initially similar embryology to the unirami and annelids and then run off on a bizarre tangent. They also have heavily modified mouthparts that are positioned behind the antennae, but the mouthparts and all the other appendages split close to where they leave the body resulting in an inner and an outer limb.

The exact evolutionary relationships of these groups is up for debate. Some argue that the three groups all evolved independently form annelids (or even more primitive ancestors in the case of the chelicerates). Some argue that the chelicerates gave rise to the biramia while the uniramia evolved separately directly from annelids. Yet others argue that the biramia gave rise to the uniramia.

The best evidence AFAIK is that what we call athropods aren’t very closely related to each other at all, and that the superficial common features are all the result of convergent evolution dictated by the independent evolution of an exoskeleton. There are only a limited number of ways to breathe with an exoskeleton, and only a limited number of ways to see, only a limited number of ways to grow. As a result the groups have independently evolved compound eyes, spiracles, moulting and so forth. That tends to be borne out when the details of those features are examined. Although the end product is the same the fundamental development is very different on all groups.

If a thing is worth doing, it is worth doing badly. - G.K. Chesterton :smiley:

Fascinating. Back in AP Bio, I came to the conclusion that the arthropods had a pretty good body plan, being versatile enough to produce all sorts of varied and useful structures (legs, mouthparts, wings, etc.), but simple enough that there was a straightforward evolutionary path to reach that complexity. In particular, I was thinking that any aliens we might happen to meet would be more likely to resemble arthropods than ourselves. If they convergently evolved multiple times on Earth alone, then I guess maybe we could expect them to also arise on other life-bearing planets.

I also note, incidentally, that even with the few breathing methods available to exoskeletal critters, the arthropods nonetheless manage to implement at least two, the spiracles of the insects and the book lungs of the arachnids. But that’s getting a bit off-subject, here.

ummm water is very transparent to the UV all the way down to 190 nm !!! Not sure where you got this from - see http://www.lsbu.ac.uk/water/vibrat.html for a spectrum

I’d expect something resembling them, but they probably wouldn’t be the (intelligent) aliens because of the size limits imposed by any plausible exoskeleton.

You know, I was kind of scratching my head over that one, because I know (from first hand experience, no less) how easy it is to get severely sunburned in the water. Also with the snow-blindness thing, where you get sunburn on your retina! :eek:

After reading the article about IR goggles, I suddenly understood the black domes over the security cams in the subway. It never occurred to me that they might be using infrared; I thought it was one-way glass or something.

Fascinating. I’m going to make some, as soon as I can get my paws on the colour filters and some welding goggles. :slight_smile:

I knew about the retina’s sensitivity to UV, and the fact that the lens of the eye doesn’t pass it. I thought that was because if it did, there would be excessive chromatic aberration between the UV and red on the retina… didn’t know about the scattering in the eye.

I’ve wondered what seeing infrared and ultraviolet would do to artistic colour theory for a long time. This link off the IR goggle page mentions

Am I right in understanding that ‘chromophores’ are the light-sensitive cells in the retina?

I want wide-spectrum eyes.

Does that mean you’ll be adding another letter to your username? :slight_smile:

yes, if everyone will now refer to me as IRcmyk from now on. And if I can make glasses that would allow me to see in the ultraviolet, that’ll be IRcmykUV. :cool:

Wouldn’t the IR and UV be additions to the emissive RGB spectrum though? For your username, you’d have to come up with two colours of pigments that reflected IR and UV…

I learned about this in a different thread. There are some women who have a fourth cone. Sorry, it doesn’t happen to men.

I’m pretty sure almost no ordinary surveillance cameras are IR, because a) there aren’t adequate IR light sources in most indoor locations, and 2) IR video would miss a great deal of info that would be important to capture, among other reasons. IR cameras may be used in places with no (visible) light, to capture things that would otherwise be invisible, but this can only be a tiny minority of situations.

I think the dark domes are ordinary gray tint and are used to mask where the camera is looking.

I went out and did it today. It’s pretty cool, although I only got everything ready an hour or two before twilight, so I didn’t have a long time to check it out. You really do need full sunlight. Open shade is completely black.

A few observations: I was surprised how quickly my eyes adjusted to IR. Less than a minute; much faster than standard dark adapting, or so it seemed. Also, I happen to have fixture in my bathroom with two incandescent and two compact fluorescent bulbs. (The CF save power, and the incandescent light up immediately.) Seen through the goggles, the incandescent were much brighter than the CF.

I’m sure you’re right about the domes just being dark tinted, but there’s actuallt plenty of IR light out there. If you’ve ever placed a visible blocked/IR transmitting filter over an ordinary CCD camera, it looks pretty normal, except that dim light look brighter than they should. Ordinary incandescent lamps throw off a lot more near IR than visible light, and even environments lit chiefly by fluorescent lamps have quite a bit of IR in them. Ordinary CCD cameras are sensitive up to about 1.3 microns, and there’s plentyt of that light to capture. most things look pretty normal,(to a black and white monitor), except that incandescent indicator lights look [i[way* brighter than they do to your eye, since they’re throwing off a lot more IR than visible.

Yes, but if Sunspace was theorizing that the domes were made of a filter such as Beatty describes on the linked site, the full output of the sun is just barely enough to make an image visible to dark adapted human eyes. Yes, cameras can be made more sensitive than the eye, but my main point was that there’s no compelling reason to use IR in most surveillance situations.

You mean like this?

Here are a few digital pictures I took today with the filters Beatty recommended, next to visible light shots of the same scenes. I’m reasonably pleased with them.

At first I thought that the IR pix were fuzzier because of the blurring effect of the filter material (5 sheets), but then I remembered that the focus point for IR is different than for visible. So I can probably get some sharper pictures next time.

Damn, that’s cool!

Does your camera pictures look like what you see with your eyes?

If I’m using a camera, how do I figure out where the IR focus point is? Will the display screen in a digital camera still work, or do I need to use an SLR style with an optical focus?

I wonder how narrow we can make the bandpass filters. What if we got some dark grey filters, so that the sensitivity of the eye at regular colours was the same as for the infrared. The we could see how the colours mix. :slight_smile:

Another idea I had: if you go over to the LED Museum, you can find reviews of light-emitting diodes (LEDs) that give light of dozens of dfferent wavelengths (i.e. colours), from deep infrared all the way through regular colours like red, yelow, green, and blue, up into the ultraviolet. These are available from electronics suppliers. It would be simple to put a bunch of them in a flashlight body, then build a switchable circuit so that you could select which colour of light to use.

Then you could see what things look like under different colours of infrared. (Of course, you might need a lot of LEDs…)

Next weekend, I hope to get some of the filter sheets. I can hardly wait!

On the IR goggles:

I used welding goggles to construct mine and left in the clear, UV blocking glass to maximise protection of my eyes from UV.

One problem I did have was making the goggles seat neat against my face so that the rubber seal blocks out all the light. At the moment I have to push the goggles against my face to prevent slivers of light coming in around my nose. Problem with having a big hooter. If anyone has a bright idea on how this can be stopped, let me know.

Yes, pretty much.

The IR focus point is closer than the visible. I noticed that in a shot in which I had set the focus to about 6 feet, the background (at infinity) was in sharp focus. So keep the focus set close in. (Back in the old days, I remember seeing lenses that had IR marks on them, for use with IR film.)

Not in real time, but…

…you can still use a digital camera if it has manually adjustable exposure. I used a Canon 10D, a digital SLR. My digital point-and-shoot (Canon SD-400) doesn’t allow for manual exposure control, so I don’t think it would work for this.

The filters are so dark that you can’t see anything through either the digital or optical viewfinders. So shooting requires long exposures and use of a tripod. Most of the shots I took were about 3 or 4 seconds (at 200 ASA). I just pointed and snapped. After the exposure I looked at the image on the LCD and made any necessary adjustments to the framing. (You could also, of course, just remove the filter for framing, and put it back for the exposure.)

I’m not sure I follow you. Do you mean a gray filter for one eye and IR for the other? I was thinking that this would be an interesting idea, but the goggles I got were the the one-piece rectangular type, not the round ones.

As I mentioned before, with these filters it takes a lot of light to see anything. But it would be interesting to try. Let us know your results.

I had this problem at first too, although it was from light coming in the side of the goggles next to my ears. Tightening the straps more tightly helped. If you have light coming in the nose slot, you might try sticking some dark cloth to the goggles in the nose slot.

Too small to work very well; you’d want infra-eyes that are bigger than the normal spectrum ones to make up for the longer wavelength of infrared. Something closer to Minbari head-bones with embedded eyes, perhaps.