Lens Disk idea

[Harry Dalek]

couple of quick and dirty photos to demonstrate the problem:

The first photo looks bleached out because there is no ir filter in the camera. Apologies for the poor resolution and bad focus too, it's a 10 year old webcam that's been abused a lot!

Thanks for your experiments ,i don't have a filter to do the same test on the ink but sounds like its invisible to IR light .

One thing i was expecting the white paper to reflect the light better than black looks about the same to me ...on my go

I also wonder if i tried it on different ink colours it might make a difference i suppose its all the same ink in chemical ? apart from what ever is used in each colour but wonder if that difference could help ..

Also this should work off mat paper right ? my working one shows poor reflection off mat white.

My daughter has coloured paper i might have a look today if the ink in that paper might work or even colouring in the black part with different pens or lead pencil .

Gary if you are there and still want the print out just send your address as a PM

[M3DVQ]

The infra red world is a surreal place. Leafy green trees are brilliant white as though they're covered in snow. Your dark blue fleece is light grey, and your eyes are hollow and dead

Dyes are generally invisible to infra red. It is apparently possible to get printer ink which does absorb infra red, but I suspect it's not cheap!

[Harry Dalek]

The infra red world is a surreal place. Leafy green trees are brilliant white as though they're covered in snow. Your dark blue fleece is light grey, and your eyes are hollow and dead

Dyes are generally invisible to infra red. It is apparently possible to get printer ink which does absorb infra red, but I suspect it's not cheap!

Hi Yes sounds like it would be a different world in IR sight...

i just tried different ink pens pencils and such also seemed to give the same result
purple seemed brighter than most but that might be just because the IR light looks purple on the camera screen ? don't know

I can only seem to get it to work instead of colours all mat paper slot shiny slot.... then i can get the pulse to work this could be also why the distance for mine to work is greater ....could again also be my IR led might need a pot might be to bright ....its either its invisible to the printer ink or the IR led or IR sensor needs a pot to adjust it ...might still be a good idea if gary wants to still test my encoder print out .

[gary]

Well thanks guys, that confirms it all very well.

What is interesting is the video Harry took of his "cut out" encoder which shows that it is working entirely in reverse that which you might expect.

In truth it is not so surprising to me as I had already noted that any glossy surface acts as a good reflector of IR light even if it is transparent. What wasn't so predictable was how little light (in comparison) is reflected by the white paper. Presumable this is due to the diffusing nature of the, somewhat rough, surface of the paper.


The next question is, why doesn't the black ink absorb a reasonable amount of the IR light?

[Harry Dalek]

Well thanks guys, that confirms it all very well.

What is interesting is the video Harry took of his "cut out" encoder which shows that it is working entirely in reverse that which you might expect.

In truth it is not so surprising to me as I had already noted that any glossy surface acts as a good reflector of IR light even if it is transparent. What wasn't so predictable was how little light (in comparison) is reflected by the white paper. Presumable this is due to the diffusing nature of the, somewhat rough, surface of the paper.


The next question is, why doesn't the black ink absorb a reasonable amount of the IR light?

Using the remotes IR led Gary was a great idea as you can test a lot of different things than the one pointing at the encoder .

It sure makes life easier seeing a reflection....i also tried some other mat paper all different colours purple and black reflect back better i think i am just not sure why white yellow and such you can not see it very well i am really not sure if it does and we can't see it as well ?

The experiment shows mat paper reflects poorly ,i think every one uses mat paper ? or the type with a shiny back ?

I made a cd transparent disk and placed that over the print out encoder to be able to adjust the missing pulse position and i didn't use it ,it must not have worked so shiny dark and shiny white must reflect to close to each other i must have a look again to make sure .

Must do a google on IR light .

[Harry Dalek]

I just been looking into IR light and i came up with this ...came across Carbon Black...

It is used in printer ink i am looking into if its just a matter of finding the right Black ink jet cartridge...?

[gary]

Yes the cd transparent disk is fatal to a good response. I think that is more to do with diffraction than reflection however.

Well, Harry, the thing that surprises me is that, and this is very basic but none-the-less factual, if something looks white to the eye it is reflecting the full spectrum of visible light, and if it looks black it is reflecting nothing in the visible spectrum - simple as that. Now infra red is just a little lower in frequency to the lowest frequency of the visible spectrum, and ultra violet is just a little higher than the highest frequency in the visible spectrum.

Now, any filter has a roll off, and it seems incredible to me that you could shine a red (lowest frequency in the visible spectrum) light on the encoder and you would still see black, i.e. nothing (I think?),and yet just a little lower in frequency it is totally reflective (ok, significantly reflective) - I see (no pun intended) that as quite remarkable, it implies something quite extraordinary is going on that is well worth knowing about.

This appears to be related to the colour response of the eye in that what appears black is not black at all (keeping in mind contrast is a big factor in what appears black and what doesn't).

EDIT: Many people do not realise that light is merely a bandwidth (or sub spectrum) within the electromagnetic spectrum (which includes radio waves, micro waves, x-rays, gamma rays) that extends from (in terms of frequency) very small (x) to 1/1.616199(97)×10−35.

A special *null* prize to someone who can tell us how to determine x and why it is not constant, and what is the significance of the constant 1.616199(97)×10−35.

[Harry Dalek]

Hi Gary looking at this dog in IR perhaps we are thinking in our eyes visible light spectrum when we should just be thinking in IR ...the black parts of the dogs face come up brighter but so does the mouth all these parts are hotter ...the white of the dogs fur looks darker because its colder both not because of its reflective colour at all ///
So thinking why does the black of the encoder look hotter than the white perhaps because black absorbs even IR like a black car is hotter in the sun than a white ???
But on the reflective surface is it like what i think you think Gary a double reflection happening seeing its own IR heat better than off a mat surface ..
I may be wrong may be right just putting it out there i find this interesting.

[gary]

Hi Harry, I am not sure but you seem to be thinking that all encoders exhibit this phenomenon - but I assure you MY encoders don't behave the same way YOUR encoders do. It is something to do with with the difference between using ink (as in your case) and toner (as in my case) - even though to the eye they appear more-or-less the same.

Heat and IR are NOT the same, it is just that HOT bodies tend to give off radiation strongly in the IR part of the spectrum (they give off visible light too and all other parts of the spectrum dependent on their temperature. The hotter the object the higher the frequency of radiation - thus it goes from IR to red to yellow, to blue and so on).

A TRUE black body is opaque and totally non reflective to ALL of the electromagnetic spectrum.

It is totally possible for something to appear black to our eyes and yet emit radiation in all of the rest of the electromagnetic spectrum including IR. This would be what we refer to as a notch filter. You are familiar with a notch filter? We use a notch filter to say, filter out 50 Hz mains hum from audio or video.

Now your printers black ink may well have a response of a notch filter (or a low pass filter) but the analogy would be that my 50Hz audio notch filter filters out 49.999 Hz - something that is not only unheard of, but is physically impossible to implement. That is why I find this phenomenon extraordinary.

I fully concede that my logic is purely restricted to the "ideal" world and that there are other factors associated from a far from ideal implementation - but you would expect this to result in a variation in DEGREE only - yet the fact that there is virtually no difference in reflectivity (read magnitude or luminosity) between a visually "white" segment and a visually "black" segment to IR is, well, astonishing.

The MOST astonishing thing is, as it appears to me, is not only does there appear to be the equivalent of a "brickwall" filter response, but that it is "naturally" occurring - totally by chance???

Now, if we had a full spectrum response over the bandwidth concerned *maybe* it's not as astonishing as I think - maybe a large part of the RED spectrum is unattenuated too so it's not such a brickwall filter as I think - if someone knows or thinks so please let me know.

BTW Harry - I may be wrong, but I sense a degree of scepticism in your belief that these "printed" encoders work at all, regardless of how they are printed. If I am correct I would draw your attention to the numerous MUTR Televisors out there that are using that self same encoder quite nicely.

PS: I had considered the difference in "thickness" of the layer of ink and a layer of toner as a possible reason. However it doesn't *seem* to have a significant effect on the visible light part of the spectrum. I guess there remains the possibility that the thickness and shorter wavelength have some correspondence - but that in itself would be remarkable.

[Harry Dalek]

Hi Harry, I am not sure but you seem to be thinking that all encoders exhibit this phenomenon - but I assure you MY encoders don't behave the same way YOUR encoders do.

Hi Gary well this is a good thing 2 ways of doing the same thing is a good and interesting .

It is something to do with with the difference between using ink (as in your case) and toner (as in my case) - even though to the eye they appear more-or-less the same.

Another case of the IR light either reflecting off some thing or absorbed ,i still don't understand if the light on the black in yours is absorbed due to the white in mine seems to do that and theres no ink on that or is there in the bleaching of the paper to white mmmm again Yakes

Heat and IR are NOT the same, it is just that HOT bodies tend to give off radiation strongly in the IR part of the spectrum (they give off visible light too and all other parts of the spectrum dependent on their temperature. The hotter the object the higher the frequency of radiation - thus it goes from IR to red to yellow, to blue and so on).

But we would be dealing with very low end IR of the spectrum so are we dealing with the invisible heat only low end red we can not see ...i am getting my head around if this frequency of light is absorbed more than reflected by black you would think white would reflect all light the same or be the best reflector apart from a shiny surface but its not the case i can see.
I can understand if some thing of a dark colour absorbs the ir light and looks hotter as in the test papers i did today purple and black were the best.

A TRUE black body is opaque and totally non reflective to ALL of the electromagnetic spectrum.

If it doesn't reflect the light pointed at it the light would be absorbed and turned into heat and reflect that so i am thinking it does as the light would have to be turned into some thing as the photons don't vanish ?

It is totally possible for something to appear black to our eyes and yet emit radiation in all of the rest of the electromagnetic spectrum including IR. This would be what we refer to as a notch filter. You are familiar with a notch filter? We use a notch filter to say, filter out 50 Hz mains hum from audio or video.

Now your printers black ink may well have a response of a notch filter (or a low pass filter) but the analogy would be that my 50Hz audio notch filter filters out 49.999 Hz - something that is not only unheard of, but is physically impossible to implement. That is why I find this phenomenon extraordinary.

I have heard of a notch filter yes low pass filter ; ) sounds like we have a pretty good filter effect.
I can see whats happening my end with the ink on the white paper i am using i don't know what really should happen as with most and your encoders what the same experiment does on these .

I fully concede that my logic is purely restricted to the "ideal" world and that there are other factors associated from a far from ideal implementation - but you would expect this to result in a variation in DEGREE only - yet the fact that there is virtually no difference in reflectivity (read magnitude or luminosity) between a visually "white" segment and a visually "black" segment to IR is, well, astonishing.

I would of expected a difference but looks like all inks are not the same don't you think the luminosity of the led and the sensitivity of the photo trany is a factor we have not looked into perhaps adjusted might get them in range to see as per normal but i do like the idea of a different encoder method .

The MOST astonishing thing is, as it appears to me, is not only does there appear to be the equivalent of a "brickwall" filter response, but that it is "naturally" occurring - totally by chance???

The laws of this universe seem to make it possible ,i do find it very interesting that 2 opposites gives the same result.

Now, if we had a full spectrum response over the bandwidth concerned *maybe* it's not as astonishing as I think - maybe a large part of the RED spectrum is unattenuated too so it's not such a brickwall filter as I think - if someone knows or thinks so please let me know.

Well not me it makes my brain hurt all i wanted to do is make a reflecting light switch.

BTW Harry - I may be wrong, but I sense a degree of scepticism in your belief that these "printed" encoders work at all, regardless of how they are printed. If I am correct I would draw your attention to the numerous MUTR Televisors out there that are using that self same encoder quite nicely.

Well at first till i made it work my way .....what i am interested in is i would like to see the reflective test via say a mutr encoder like i did on mine ...how well it reflects and absorbs light on the black ink and white paper there must be a difference if any one out there in NBTV land has a remote an encoder and a digital camera most IR sensitive i for one would love to see the results .

PS: I had considered the difference in "thickness" of the layer of ink and a layer of toner as a possible reason. However it doesn't *seem* to have a significant effect on the visible light part of the spectrum. I guess there remains the possibility that the thickness and shorter wavelength have some correspondence - but that in itself would be remarkable.

There factors as i see it the paper the ink yes how thick the ink layer is printed on the paper and the led photo trany but doing the ir remote test the last 2 i am a bit ify thats a problem now , bit of a puzzle .

[M3DVQ]

have a look at this page: http://www.penguinslab.com/IR.htm

particularly the graph of reflectivity vs wavelength of different surfaces. Foliage is an especially interesting one. Purple/blues are absorbed while green is reflected (as we know). Orange/Red is also absorbed well but then the reflectivity skyrockets as we get into the near-IR.


Remember that the reason we use a chemical as an orange dye say, is that it absorbs light well in a broad peak between the violet and orange. A blue dye absorbs light well in a peak between green and red.
If you mix all the chemicals together you get something that has absorption peaks across the visible range giving you a nice dark colour ink. No chemicals are added specifically to absorb IR as there is simply no need to make things black under IR usually.

In other words you shouldn't really think of dyes as a low pass filter with a sharp attenuation as you get to the infra red. Each dye is a frequency band which mixed together notch out certain colours in what is reflected as it were. If you were to image down deep into the UV wavelengths you'd see a similar things, though as the light gets higher in frequency and more energetic all sorts of odd things start to happen like fluorescence or chemical changes.

[M3DVQ]

here are the spectra of some different dyes:

[gary]

have a look at this page: http://www.penguinslab.com/IR.htm

particularly the graph of reflectivity vs wavelength of different surfaces. Foliage is an especially interesting one. Purple/blues are absorbed while green is reflected (as we know). Orange/Red is also absorbed well but then the reflectivity skyrockets as we get into the near-IR.


Remember that the reason we use a chemical as an orange dye say, is that it absorbs light well in a broad peak between the violet and orange. A blue dye absorbs light well in a peak between green and red.
If you mix all the chemicals together you get something that has absorption peaks across the visible range giving you a nice dark colour ink. No chemicals are added specifically to absorb IR as there is simply no need to make things black under IR usually.

In other words you shouldn't really think of dyes as a low pass filter with a sharp attenuation as you get to the infra red. Each dye is a frequency band which mixed together notch out certain colours in what is reflected as it were. If you were to image down deep into the UV wavelengths you'd see a similar things, though as the light gets higher in frequency and more energetic all sorts of odd things start to happen like fluorescence or chemical changes.

I have to come back to analyse you comment more closely but a brief scan indicates you may have misinterpreted my comment.

The issue here is that black (as perceived by the naked eye) is the absence of all visible colours. true black is the absence of all colours (or frequencies) period.

I am not suggesting these dyes ARE lowpass filters - merely that a lowpass filter could produce the phenomenon we are seeing here.

As I mentioned, sure, it is possible to create a notch filter that filters out all visible light and leaves all other frequencies unattenuated - what I am saying it seems astonishing to me that such a notch filter could be created, naturally, that would produce a filter with such a steep roll of on the low frequency edge that it would not attenuate IR to any great extent.

I will examine the curves more closely when I get back tonight - perhaps that is not as remarkable as it intuitively (at least to me) seems.

Cheers.

[M3DVQ]

As I mentioned, sure, it is possible to create a notch filter that filters out all visible light and leaves all other frequencies unattenuated - what I am saying it seems astonishing to me that such a notch filter could be created, naturally, that would produce a filter with such a steep roll of on the low frequency edge that it would not attenuate IR to any great extent.

My point is that it's not natural at all. The dyes are selected precisely because they absorb the visible wavelengths. (no-one wants to buy clothes dyed a "colour" that you can't see, and outside of a few uses like ours, no-one wants to print that "colour" either)

[Harry Dalek]

have a look at this page: http://www.penguinslab.com/IR.htm

particularly the graph of reflectivity vs wavelength of different surfaces. Foliage is an especially interesting one. Purple/blues are absorbed while green is reflected (as we know). Orange/Red is also absorbed well but then the reflectivity skyrockets as we get into the near-IR.

Thats an interesting chart ....but on the photos i would think the clouds would be black they seem very bright normal white in IR..

Foliage seems yes the best from that chart wonder if its because most are shiny trying to think of any that isn't i am sure there is ,i will look and do a Gary IR test ....

Perhaps i should have an encoder made of leaf !...now that would be different

I found dark colours seemed a bit better on reflecting IR black and purple were the best on coloured paper i tried , have to look into this green thing
again if different chemicals that make green are the same or not ...as we seem to have this effect on the black printer ink oils aren't oils as they say .