Economy thermal imager?

This appears to me that you were seeing the very-dimly-glowing tip and maybe the likely-slightly-hotter heating-element-area mostly with scotopic vision.

450 C is 723 K. The surface over the heating element was likely somewhat hotter, likely mid to upper 700's K.

The 798 K "Draper point" appears to me to be the threshold of achieving significant stimulation of photopic vision to the point of seeing color more than gray.

What wavelength range is your "near-IR sniffer" good at, and what radiant power density in that wavelength range is lowest it will sense? If you report this, I can figure temperature necessary to achieve this.

I am not surprised - that is 673 K.

I consider myself optimistic at thinking that I may be able with best dark adaptation to dimly see with blurred outlines and no color, incandescence at 700 K.

I calculate the following values of candela per square centimeter to photopic vision corresponding to the following temperatures low enough to achieve glow so dim as to be seen primarily by scotopic vision despite spectral content at wavelengths long enough to favor photopic:

775 K: 3.25 E-7 (s/p ratio is .131 on a scale where 555 nm monochromatic yellow-green = 1)

750 K: 1.22 E-7 (s/p ratio is .119 on the above scale)

725 K: 4.27 E-8 (s/p ratio is .107 on the above scale)

700 K: 1.40 E-8 (s/p ratio is .096 on the above scale)

===============

Temperature at which s/p ratio achieved by a blackbody is "unity" as in same as that of 555 nm yellowish-green monochromatic narrowband light:

2093 K,

which I have determined that a USA-usual 120V 100W lightbulb of "Big 3 brand" and rated to last-on-average 750 hours and to produce-on-average 1670-1750 lumens at 120 volts, to achieve at around

53-54 volts, maybe give or take another volt.

I am aware that a few lower-current longer-life vaccum-containing incandescents have a fair chance of having color temperature this low or slightly lower. However, it appears to me that more-usual for tungsten incandescent lamps with design current low enough to be served better by vacuum than by argon-nitrogen gas fill, along with design life expectancy around 2,000-3,000 hours, is for color temperature to be not far from

2360 K (which achieves s/p ratio of 1.16 on scale where 555 nm achieves unity).

The USA-usual 120V 100W incandescent with rated average life expectancy of 750 hours, rated to produce 1670-1750 lumens, and having CC-6 or CC-8 filament, and of "Big 3 brand", appears to me to typically have color temp. of 2870 K (2865 K by a slightly older definition revised by a redetermination of one of 2 constants in the "Blackbody Formula"), appears to me to achieve s/p ratio of about 1.42.

I hope the above supports my impression that human photopic and scotopic vision have nonlinearities that differ from each other. I sense that there is dynamic range compression achieved by both, less for human photopic vision than for human scotopic vision.

I sense that human scotopic vision achieving greater dynamic range compression than human photopic vision does, is the explanation for seeing barely/hardly/minimally/dimly - incandescently-hot objects with color "degrading to gray" (my words) as temperature decreases from about 800 K or so to mid-700's K or so.

- Don Klipstein (Jr) ( snipped-for-privacy@misty.com)

I know what thermal imaging is. I do not need a primer.

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

That figures, but does scotopic vision also have resolving power at the centre of vision? I was definitely seeing better imaging there..

Agreed. I'd have tested that, but the iron only went so far.. :)

Not really sure.. I built it from various RF plug parts and a couple of button cells driving directly in series, an phototransistor and a high- brightness green LED that happened to put out well at very low currents.

I think the phototransistor is an IR type from Maplin, 3mm package with spectral peak response at 880 nm. Current varying betweem 0.1 mA and 20 mA (which is why it seems so suited to direct LED drive). Those currents are specified for 1000 lux and Vce of 3V but it saw less by one LED Vf, and its sensitivity was further reduced by an IR pass filter made from the head of a dark IR LED. I'd cut it off, polished (crudely, on a paper laid on glass), then placed nose to nose to focus from a 5mm diameter region for best coupling into the phototransistor while excluding any visible light.

This thing has been generally useful for seeing IR in various conditions where it it would be within low visible intensities if it were visible at all.

Yeah, just confirming that I couldn't. :) I could have tested at what point between the two I lost sight of it, but it would taken a long time and not proved a lot.

Likely enough, I think. When I tried the 400°C test I thought I had seen something but I tried the obvious test of sheilding it with my hand, and the consciousness of the heat being shielded and the slight phosphenes (or whatever they're called when slight neural generated effects occur) dominated it. Even if I did see it it was lost in noise and loss of focus. So it was doubt, rather than absolute nonseeing, so I am sure that at 425°C it ought to be visible.

I read all that but I don't think I could have done it. Lets just say I make an unusually good guinea pig. :)

I agree with the claim that scotopic vision has greater dynamic range though. That fits my experience directly.

Possibly related to your comment on colour degrading, or perhaps not, is the IR lased diodes. When I have seen them (5mw single mode types, looked at directly at range greater than 1 foot, almost certainly eye-safe conditions) they go beyond the wine or rubt reds of visible types. The impression is of a maroon colour. (Yep, maroon, I ought to have mentioned it earlier in this thread, no? >:) And what makes THAT interesting is that it implies a bluish interpretation! Interesting given that deep violet at the other end hints at a reddish interpretation of what is just a very deep blue. Life is full of cylic/linear transforms, but this is the single weirdest one I know.

In article , Lostgallifreyan wrote in part:

This reminds me of sensing some barely visible IR LEDs as emitting a slightly orangish shade of red. I have seen their spectra with a diffraction grating, and I know that I am seeing only very long wavelengths past 750 nm, generally past 800 nm. I have seen the slightly orangish shade of red in the long wavelength spectral region shown by the diffraction grating, with the shorter wavelength end of the spectral band appearing to me closer to pure red in color.

I have heard of this being called "color reversal" or "infrared color reversal".

As for the soldering iron tip becoming more focused but still appearing gray when viewed with central vision: I suspect that there are some rods in central vision, in smaller and more closely spaced clusters to achieve better resolution. Possibly photopic vision plays enough of a role to increase sensation of resolution, however. However, I do see dimly gray-appearing incandescent objects becoming invisible when viewed entirely with the most central degree or two of vision. And when I look at such an object that partially falls into the supposedly rod-free most-central degree or two of vision, I sometimes tend to see the whole thing anyway - maybe I get prone to "seeing things" under such conditions.

- Don Klipstein ( snipped-for-privacy@misty.com)

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

Weird. I have read of this before, but I don't know why it should be. The maroon I sort of understand, it fits with a kind of mapping of spectrum as circle, a standard practise in Microsoft colour picker dialogs for example.. Maybe our brains give interpretations to fit models we already have? These models may work at a very primal level too.

Brains again.. I've noticed mine has an amazing ability to fill in missing detail. Can be the cause of error as much as a cure for it. It's entirely possible that although I do see that weakly hot iron in the centre of my vision, any impression of better definition is purely my brain filling in because it expects it, and knows what the iron looks like already. The silhouette of the guard coil was real though, it presented itself as an unfamiliar effect somehow even though logically I should have expected to see it. I've learned to gauge when my brain is 'filling in' because when that happens the impression often has a suspiciously familiar aspect when a true new observation probably could not feel that way. But I usually avoid this when trying to establish a fact, it's the equivalent of trying to design for an op-amp at an extreme of its capability.

One thing I do remember, looking at a comet. That vanished when I looked directly at it. The only way to see it was with peripheral vision, and to keep moving slowly, too, so it triggered new cells and didn't get lost in noise and distractions. Different spectrum of light, but still obviously scotopic..

is

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Simply put, just harmonics (frequency doubling/tripling). Many more complex things are significant contributors as well.

viewed

look

whole=20

missing=20

entirely=20

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that=20

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This is back some decades ago when i was a teen. My eyes were really sensitive, bright summer daylight caused me pain. BTW the soldering iron was an old ungar imperial with a 40 W cartridge.

"JosephKK" wrote in news: snipped-for-privacy@4ax.com:

Seems doubtful to me. There is a doubling effect in the materials of the eye apparently, people exposed to 1064 nm beams have reported seeing a green flash of doubled-to-532nm light. I can't cite where I saw it because I can't remember but it has been mentioned on alt.lasers at times. It's a result of high intensity though, not low. It takes a lot of energy to produce the nonlinear effects needed to do it.

I don't know what to think though, most explanations I've seen have problems that make them unlikely. For example, the intensity needed to fire off a strong green flash in the eyeball might need to be so strong that the last thing the observer would be concerned with would be the perceived colour..

No. Frequency doubling requires very high light intensities and usually a crystal lattice with a heavy highly charged ion in it.

It is more likely to be a quirk of the light sensitive pigments of the eye. A lot of nominally blue pigments and dyes have near IR leaks and I expect the eye pigment is no different. Also at the low sensitivity needed for near IR most of the colour vision is gone for me so it is essentially grey with a hint of orange. NB red is constructed by the brain as yellow-green. The eye cones are sensitive to yellow, green and blue. Red is a construction of the brain.

You can have fun with this perceptual feature by using a neodymium filter over the eyes which creates out of gamut colours for the brain to contend with that are "redder than red" and "greener than green".

Regards, Martin Brown

On Wed, 22 Jul 2009 16:00:31 -0700, Archimedes' Lever wrote (in article ):

When i search Frys.com for "infrared" I get all kinds of IR communication devices (headphones, etc.), an intrusion-sensor security system, and one security camera that uses IR illumination.

Is this what you mean? ::

Thanks.

Martin Brown wrote in news:Fruhm.267740$ snipped-for-privacy@newsfe15.iad:

That relates to what Don Klipstein said, and I've been thinking about that.. it's ame for me if the source is low intensity, broadband, and at edges of IR. Orangish greyish brownish.. But what if the source is narrowband, much deeper into IR, and fairly strong? To me such sources (unlensed 5 mW laser diodes, etc) look maroon, a distinct red that is so deep and dark it is to red as deep violet is to blue. And both ends of the spectrum seem to reach toward each other like the closing of a circle. Anyone else see it this way?

NB red is constructed by the

Where can I get one? This needs trying. What form is the neodymium in, obviously not metal sheet... Doped glass?

s

Yes, that is what not to buy. ;-)

This is an example of a very sensitive B&W camera that has some near IR response

164C Unfortunately, this one is CS mount. I can't say for sure if you can use a C mount lens on it. I have an older version that is C mount. The idea is you get a large aperture c-mount lens, which isn't all that hard these days if you want something that is purely mechanical (i.e no electronic iris). Ebay has no shortage of C mount lens. If you get serious about this and want a follow up, start another thread as this one is pretty much hijacked.

Years ago, I collected a set of LEDs with various wavelengths. One was 700 nm. It was a very pleasant (to my eye) deep red.

It might have had a hint of purple in it, but I don't think that's how I would have described it. If you had used that word I probably would not have said you were nuts. (Again, that's from several years ago.)

--
These are my opinions, not necessarily my employer's.  I hate spam.

Perfect proof that most in the group are idiots.

Not one comment on this well known anomaly as the years ticked by.

Now, the idiots are even talking about a reduced range setup.

This toy was around in 1987. I am sure many can be found in the used channels.

You guys should talk to this guy. He knows exactly what he is doing.

His name is waterhed

The nominal peak wavelength of an LED is +/- 20nm so there would be some visible deep red component in the wings unless you also had a long pass filter. A lot of IR LEDs have a black organic dye in them to mask any trace of visible red emission. 750nm & 820nm ones look pretty well black to me.

Regards, Martin Brown

Where would one find such a lens to replace the standard lens?

Thanks.

Did you think to try Edmund Scientific or some optical lens coating supplier?

The FP uses a CCD so can't work as a thermal imager. Near IR, maybe, but that isn't germanium lens territory.

Most digital cameras work nicely in the near IR.

John