The hackspace sub-thread and various other things have made me realise that it might be possible to seriously attack a project that has been floating around my brain for several years.
The first element I need to get working is a tunable light source. For now, from near-visible IR through to top of visible spectrum would be enough. I think I need a moderately tight band of frequencies. It does not need to be super bright, nor does it need to light a room. A few square inches of illumination, a few inches from the source, and visible in a darkened room might be enough. But until I try it, I do not know - that could be an underestimate and brighter is certainly not a problem. And I need to be able to set the frequency quite accurately.
Anyone got any suggestions as to how to achieve that in a diy way? And for a pittance.
How do those colour detectors work. They must be quite cheap, the Cobolt Speechmaster device complete is around 60 quid, but it might not have the resolution you want. k Brian
An incandescent lamp and a diffraction grating is the only way to do it reliably over such a wide range. Edmund scientific will sell you some. You might be able to buy something off the shelf from Anchor surplus or the US Surplus Shed (beware of import duty and freight charges).
LED technology can give you various colours but the bandwidth is 50-80nm so "yellow" includes some red and green etc. The red includes some orange etc. Greens include some blue and some yellow. Modern blue and green LEDs are far more saturated than the early ones.
You can see their spectrum fairly easily using a shovelware CD as a reflection grating.
Use a prism of dispersive glass. And a wideband source like an incandescent lamp
A friend of mine designs and builds spectrometers.. you heat a material up red hot and the a stepper motor rotates a prism, so the whole emissions spectrum passes through a tightly focussed (collimator) on to a photocell. Something like that.
That charts the entire spectrum and then if suitable calibrated, he looks for signatures of things like lead and mercury, in software, compared with specially perapred samples with 'industrial limits' of the particular contaminants.
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jock@ will find him. He may have some suitable optics 'left over'
Id forgotten diffraction gratings, yes that works as well.
LEDS are at best monochromatic with multiple spectral lines. Only incandescent gives a whole spectrum with ALL freq1uenies present, and that can be contaminated by the presence of certain fluorescent type materials.
I have a suspicion that certain diseases might affect absorption/emission of light. So I want to see whether that is the case
- sort of in the mould of the tricorder challenge. :-)
I would be perfectly happy with the ability to take a series of photographs and examine carefully afterwards. The end result might be as simple as a standard xenon flash with several filters. But for now, I need to examine what happens in normal health and in disease and find which frequencies I need to look at. (I do have specific diseases in mind and, therefore, potential victims.)
Although I think you are probably barking up the wrong tree you can get narrow band filters to only pass certain wavelengths and by tilting them detune them by cos(theta) for H-alpha (656nm) red and OIII(~500nm) cyan relatively cheaply. I doubt if you can detune them enough to get the full range so you might have to buy one exotic filter inbetween at full price from Edmund (they do practically everything in 10nm steps).
The astronomically interesting narrowband filters are mass produced at
1.25" diameter and available for £50-£100 each from various dealers.
I should warn you that narrowband imaging is an already well established technique and in the near IR works to spot dead and dying trees in forests before it is at all obvious in the visible.
During WWII people with an unusual form of colour blindness that allowed them to see near IR were much sought after because they could see through camouflage in that branches no longer connected to roots looked different to them as they saw light in the near IR.
You can achieve the same sort of effect with normal visions by looking at the world through unexposed developed slide film which severely attenuates visible light whilst passing near IR. Once your colour vision returns you see the world with a powerful near IR bias. DO NOT under any circumstances look at the sun as permanent eye damage can result - dye based films allow damaging amounts of IR through whilst maintaining an apparently comfortable visible light level.
There are no pain receptors in the retina so you only feel the excruciating pain much later. This happens during solar eclipses too when the total amount goes down but the surface brightness does not!
The blind Belgian experimenter Plateau who destroyed his own sight by persistance of vision experiments that involved staring fixedly at the sun for just 25s and went blind in later life as a result.
There is at least one disease that makes the skin look different under UV light. I was tested for it, which is how come I know, but I don?t have it, which is how come I can?t remember what it was. However, a google search suggests tuberous sclerosis is one such disease, for which a Wood?s lamp is used. The wikipedia page on Wood?s lamps says something about dermatology too.
It is that sort of thing I have some hope for - not that disease, though!
Some time ago I saw someone photographing documents at multiple frequencies, then combining the results. He was managing to pull out an astonishing level of detail which was otherwise inaccessible.
With a disease as rare as perhaps 150 sufferers in the UK (and that seems feasible but not certain), not much research has actually been done.
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