| Sysop: | Amessyroom |
|---|---|
| Location: | Fayetteville, NC |
| Users: | 28 |
| Nodes: | 6 (1 / 5) |
| Uptime: | 58:47:27 |
| Calls: | 424 |
| Calls today: | 2 |
| Files: | 1,025 |
| Messages: | 90,903 |
| Posted today: | 1 |
Not quite, but, close enough...
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
I've worked with true colorimeters (dual wavelength) in the past.
But, they were optimized to look for specific wavelengths.
I calibrate the light emitted by my monitors with a device,
but it controls the light source to do so.
With no knowledge of the actual (visible) spectrum impinging on
a sensor (and a bit of time to integrate results), how can I
do this short of swapping individual filters in front of the
sensor(s)?
Not quite, but, close enough...
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
I've worked with true colorimeters (dual wavelength) in the past.
But, they were optimized to look for specific wavelengths.
I calibrate the light emitted by my monitors with a device,
but it controls the light source to do so.
With no knowledge of the actual (visible) spectrum impinging on
a sensor (and a bit of time to integrate results), how can I
do this short of swapping individual filters in front of the
sensor(s)?
On Sat, 17 May 2025 12:30:38 -0700, Don Yx3ZbRTwkboNHcYYefd34pvzEKKty4RSFiiA4v0BSw_gbiEQH-khaK5lIXJ36q2q2xqW39hJj34hYp1MPTT9w4wb0RRE01F52nClp8J-VhECWQ18IWoopERU1Pl8khD8T_UPIBnauk.iFb6dsfIy8kEJvdCzNVyv8buyH2ji-Budd1i9iTh3IE&dib_tag=se&keywords=spectrometer+handheld&qid=1747511016&sprefix=
<blockedofcourse@foo.invalid> wrote:
Not quite, but, close enough...
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
I've worked with true colorimeters (dual wavelength) in the past.
But, they were optimized to look for specific wavelengths.
I calibrate the light emitted by my monitors with a device,
but it controls the light source to do so.
With no knowledge of the actual (visible) spectrum impinging on
a sensor (and a bit of time to integrate results), how can I
do this short of swapping individual filters in front of the
sensor(s)?
The people who make spectrometer-type instruments seem to be in a
battle for ever finer resolution.
I want a spectrometer that spans 400 to 1600 nm, or at least 800 to
1600. I want to know if a 1310 nm laser is about 1310 and not by
accident 1550 or something.
I was thinking about making such an instrument. A few filters and a
few photodiodes might work, with some overlap for interpolation.
A rotating, graded filter and one wideband detector could work.
Or a grating and a couple of detectors, with software to resolve
ambiguities.
Maybe just three detectors with different wavelength peaks.
We did buy a couple of fiber WDM splitters, which can, for instance,
tell us if a laser is 880 or 1300 or some such.
Are there toy-level visual spectrometers?
https://www.amazon.com/EISCO-Premium-Quantitative-Spectroscope-Accuracy/dp/B00B84DGDA/ref=sr_1_3?crid=21PO5QTTGGA06&dib=eyJ2IjoiMSJ9.IwA9B16820dPfj5ct0JEivvGqDD0YV5wFHFcG9c1Xss1BCoKEJvHFm_dYkhhHHK8lICo1KuioeQ85usmShFPtgMSSa0gzI2E-_
Cool. I just ordered one.
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
On Sat, 17 May 2025 12:30:38 -0700, Don Yx3ZbRTwkboNHcYYefd34pvzEKKty4RSFiiA4v0BSw_gbiEQH-khaK5lIXJ36q2q2xqW39hJj34hYp1MPTT9w4wb0RRE01F52nClp8J-VhECWQ18IWoopERU1Pl8khD8T_UPIBnauk.iFb6dsfIy8kEJvdCzNVyv8buyH2ji-Budd1i9iTh3IE&dib_tag=se&keywords=spectrometer+handheld&qid=1747511016&sprefix=
<blockedofcourse@foo.invalid> wrote:
Not quite, but, close enough...
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
I've worked with true colorimeters (dual wavelength) in the past.
But, they were optimized to look for specific wavelengths.
I calibrate the light emitted by my monitors with a device,
but it controls the light source to do so.
With no knowledge of the actual (visible) spectrum impinging on
a sensor (and a bit of time to integrate results), how can I
do this short of swapping individual filters in front of the
sensor(s)?
The people who make spectrometer-type instruments seem to be in a
battle for ever finer resolution.
I want a spectrometer that spans 400 to 1600 nm, or at least 800 to
1600. I want to know if a 1310 nm laser is about 1310 and not by
accident 1550 or something.
I was thinking about making such an instrument. A few filters and a
few photodiodes might work, with some overlap for interpolation.
A rotating, graded filter and one wideband detector could work.
Or a grating and a couple of detectors, with software to resolve
ambiguities.
Maybe just three detectors with different wavelength peaks.
We did buy a couple of fiber WDM splitters, which can, for instance,
tell us if a laser is 880 or 1300 or some such.
Are there toy-level visual spectrometers?
https://www.amazon.com/EISCO-Premium-Quantitative-Spectroscope-Accuracy/dp/B00B84DGDA/ref=sr_1_3?crid=21PO5QTTGGA06&dib=eyJ2IjoiMSJ9.IwA9B16820dPfj5ct0JEivvGqDD0YV5wFHFcG9c1Xss1BCoKEJvHFm_dYkhhHHK8lICo1KuioeQ85usmShFPtgMSSa0gzI2E-_
Cool. I just ordered one.
Don Y <blockedofcourse@foo.invalid> wrote:
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
Spinning or oscillating prism?
On 17/05/2025 20:30, Don Y wrote:
Not quite, but, close enough...
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
Short answer is you can't - at least without making some *very* questionable assumptions. It is even worse now with narrowband LEDs.
If you are allowed to make the assumption of a radiant perfect black body (something that doesn't exist) then it is much easier.
I've worked with true colorimeters (dual wavelength) in the past.
But, they were optimized to look for specific wavelengths.
True colorimeters were designed to match visible colours pretty much exactly under *any* lighting conditions (extremely tough problem). The first that actually worked well enough was the Imperial Match Predictor which ISTR was an
analogue computer made in the UK by ICI strictly for internal use only. I don't
think any documentation survives.
There was a US made spectrometer which formed a part of it whose manufacturers
name escapes me for the moment. Got it Hardy Spectrophotometer:
https://collection.sciencemuseumgroup.org.uk/objects/co11842/ge-hardy-spectrophotometer-c-1940
That model isn't quite the right one but it is close.
Now any suitable paint test chart and a mobile phone will do the job.
I calibrate the light emitted by my monitors with a device,
but it controls the light source to do so.
If you are serious about doing this right then a 2D CCD sensor and a prism hires grating combo at right angles will allow you to quantify the entire visible spectrum at ultra high resolution. Be careful though Perkin-Elmer (and
others) have some very good lock out patents on this trick (may be about to expire).
A few people can see longer wavelengths than most with an extra type of cone cell. They were sought after in WWII (pre thermal IR band imaging) because they
could see the difference between live foliage still growing and cut down dying
foliage used as gun emplacement camouflage.
Denatured chlorophyll looks much darker to them.
With no knowledge of the actual (visible) spectrum impinging on
a sensor (and a bit of time to integrate results), how can I
do this short of swapping individual filters in front of the
sensor(s)?
Measure the intensity at all wavelengths in a single shot.
PE OES instrument in the early 1990's was the first with this.
(I forget the model number) I was seriously impressed with it.
Don Y <blockedofcourse@foo.invalid> wrote:
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
Spinning or oscillating prism?
Not quite, but, close enough...
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
On 5/17/2025 2:03 PM, Martin Brown wrote:
If you are serious about doing this right then a 2D CCD sensor and a
prism hires grating combo at right angles will allow you to quantify
the entire visible spectrum at ultra high resolution. Be careful
though Perkin-Elmer (and others) have some very good lock out patents
on this trick (may be about to expire).
Again, not looking to make an "instrument". The phone idea may work
if the CCDs don't freak out with high intensity sources.
If you are serious about doing this right then a 2D CCD sensor and a
prism hires grating combo at right angles will allow you to quantify the entire visible spectrum at ultra high resolution.
On 5/17/2025 2:03 PM, Martin Brown wrote:
On 17/05/2025 20:30, Don Y wrote:
Not quite, but, close enough...
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
Short answer is you can't - at least without making some *very* questionable >> assumptions. It is even worse now with narrowband LEDs.
If you are allowed to make the assumption of a radiant perfect black body
(something that doesn't exist) then it is much easier.
I'm not looking for a laboratory grade instrument. (hence the
"corner cutting" caveat).
Rather, "how does the light falling on THIS body compare to the
light on this OTHER body" (using the same measuring instrument)
I've worked with true colorimeters (dual wavelength) in the past.
But, they were optimized to look for specific wavelengths.
True colorimeters were designed to match visible colours pretty much exactly >> under *any* lighting conditions (extremely tough problem). The first that
actually worked well enough was the Imperial Match Predictor which ISTR was an
analogue computer made in the UK by ICI strictly for internal use only. I don't
think any documentation survives.
Ours controlled the color temperature of an incandescent lamp
"seen" through a pair of filters. Then, compared the detected
signal from the sample under test (inserted between the emitter
and detector) in the same short time interval, looking for a
particular color shift (analyzing blood assays)
Again, you don't care WHAT "color" it is, just how the chemistry
altered the color within a band of expected results.
But, that system KNEW what to expect (expectations were dependent
on the actual assay being run)
There was a US made spectrometer which formed a part of it whose manufacturers
name escapes me for the moment. Got it Hardy Spectrophotometer:
https://collection.sciencemuseumgroup.org.uk/objects/co11842/ge-hardy-spectrophotometer-c-1940
That model isn't quite the right one but it is close.
Now any suitable paint test chart and a mobile phone will do the job.
How durable are the CCDs used in phones? Especially to high intensity light sources?
I calibrate the light emitted by my monitors with a device,
but it controls the light source to do so.
If you are serious about doing this right then a 2D CCD sensor and a prism >> hires grating combo at right angles will allow you to quantify the entire
visible spectrum at ultra high resolution. Be careful though Perkin-Elmer (and
others) have some very good lock out patents on this trick (may be about to >> expire).
Again, not looking to make an "instrument". The phone idea may work
if the CCDs don't freak out with high intensity sources.
A few people can see longer wavelengths than most with an extra type of cone >> cell. They were sought after in WWII (pre thermal IR band imaging) because they
could see the difference between live foliage still growing and cut down dying
foliage used as gun emplacement camouflage.
Also folks who are truly colorblind. Camouflage looks different than
natural foliage when you are just looking at the values without the
hues to distract.
Denatured chlorophyll looks much darker to them.
With no knowledge of the actual (visible) spectrum impinging on
a sensor (and a bit of time to integrate results), how can I
do this short of swapping individual filters in front of the
sensor(s)?
Measure the intensity at all wavelengths in a single shot.
Or, leverage the fact that the spectrum won't be changing in
the short term (for some value of "short") and cycle a set
of filters (rotating disc?) between the detector and source.
Again, if you aren't looking for repeatability instrument to
instrument, this may be good enough to answer the question above.
PE OES instrument in the early 1990's was the first with this.
(I forget the model number) I was seriously impressed with it.
On 18/05/2025 03:29, Don Y wrote:
On 5/17/2025 2:03 PM, Martin Brown wrote:
If you are serious about doing this right then a 2D CCD sensor and a prism >>> hires grating combo at right angles will allow you to quantify the entire >>> visible spectrum at ultra high resolution. Be careful though Perkin-Elmer >>> (and others) have some very good lock out patents on this trick (may be
about to expire).
Again, not looking to make an "instrument". The phone idea may work
if the CCDs don't freak out with high intensity sources.
CCDs are almost indestructible unless you point them at the sun. Even then they
handle it much better than a human eye. Webcams are probably a lot cheaper though. If you find one of the paint firm's colour matching apps and test chart
it may already do what you want or close enough.
If you just want to color match then your phone camera is dandy. There are apps used by printers and film lighting cameramen to do just that. ISTR chromlink ?
On 5/17/25 23:03, Martin Brown wrote:
If you are serious about doing this right then a 2D CCD sensor and a prism >> hires grating combo at right angles will allow you to quantify the entire
visible spectrum at ultra high resolution.
use a CD https://youtu.be/EoAZ-u6hn6g?si=Mv-DfJ5swtq2-j1X&t=98 :)
eons ago we used some CCDs as detectors for X-ray fluorescence, some had weird
formats like 1024x64 pixels so I assume they were really made for spectroscopy
On 5/18/2025 5:37 AM, Martin Brown wrote:
On 18/05/2025 03:29, Don Y wrote:
On 5/17/2025 2:03 PM, Martin Brown wrote:
If you are serious about doing this right then a 2D CCD sensor and a
prism hires grating combo at right angles will allow you to quantify
the entire visible spectrum at ultra high resolution. Be careful
though Perkin-Elmer (and others) have some very good lock out
patents on this trick (may be about to expire).
Again, not looking to make an "instrument". The phone idea may work
if the CCDs don't freak out with high intensity sources.
CCDs are almost indestructible unless you point them at the sun. Even
then they handle it much better than a human eye. Webcams are probably
a lot cheaper though. If you find one of the paint firm's colour
matching apps and test chart it may already do what you want or close
enough.
The way it was described to me (how does the light falling on this body compare
to the light on some other body) suggests it was expected to receive
radiant
light directly (not reflected light of of two bodies that have different reflectance characteristics)
But, I don't know how intense the light would be.
I was asked because of my past experience with the colorimeter shining
light
directly onto the detector, through filters. (I've seen products that can tell you what color an object is, etc., using reflectance)
On 5/17/2025 2:03 PM, Liz Tuddenham wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
How can I determine the spectrum of incident light on a sensor,
in general? Then, how many corners can I cut to sacrifice resolution
and accuracy?
Spinning or oscillating prism?
That might be better than a varied filter. But, probably require finer control (or sensing) of its current orientation.
On 5/18/2025 6:13 AM, Lasse Langwadt wrote:
On 5/17/25 23:03, Martin Brown wrote:
If you are serious about doing this right then a 2D CCD sensor and a
prism hires grating combo at right angles will allow you to quantify
the entire visible spectrum at ultra high resolution.
use a CD https://youtu.be/EoAZ-u6hn6g?si=Mv-DfJ5swtq2-j1X&t=98 :)
eons ago we used some CCDs as detectors for X-ray fluorescence, some
had weird formats like 1024x64 pixels so I assume they were really
made for spectroscopy
As mentioned elsewhere, how do they fare when light is shining directly
on the
sensor? How do you keep it from saturating -- dark lens to attenuate
the signal?
The way it was described to me (how does the light falling on this body compare
to the light on some other body) suggests it was expected to receive radiant >> light directly (not reflected light of of two bodies that have different
reflectance characteristics)
But, I don't know how intense the light would be.
As ever the devil is always in the details. Identical colours but with different surface finishes can look incredibly different. Vantablack is very much like looking into the void it is quite literally blacker than black!
Any other "black" looks grey next to it.
I was asked because of my past experience with the colorimeter shining light >> directly onto the detector, through filters. (I've seen products that can >> tell you what color an object is, etc., using reflectance)
You can trick almost any sensor. Human eye can be quite easily misled by didymium glass which is a narrowband Na-D blocking filter used to see into a bright yellow sodium flame when glassblowing.
Side effect is to produce cartoon like out of gamut colours when the brain tries to compute colours from the cones. Its apparent colour varies radically with the source of illumination.
The same property is shared with the natural gemstone Alexandrite.
https://en.wikipedia.org/wiki/Chrysoberyl
Such materials are rare and highly prized for their strange behaviour.