Re: "Colorimeter"

   Martin Brown <'''newspam'''@nonad.co.uk> wrote:

On 20/05/2025 18:43, Don Y wrote:

On 5/18/2025 2:15 PM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:
>

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.

>
If it is spinning steadily, all you need is a synchronising pulse at
some point once per revolution and a wide spectrum photocell with an
optical slit and a lens.  Software can work out the wavelength from the
rotational speed and the known characteristics of the prism.  The

 
Of course.  But, if spinning faster than your integration interval,
I suspect any jitter in your angular resolution might be difficult
to factor out of the mix.
 
This would, instead, suggest a slower rotation so the prism feeds
the detector a single wavelength for a longer (continuous) period.

 
I really wouldn't consider anything with moving parts. You can get
reasonable grade replica grating for low resolution spectroscopy from
the likes of Edmund scientific (intended for school labs).
 
https://www.edmundoptics.co.uk/c/gratings/621/#27766=27766_s%3AClear%2BPol
yester%2BFilm
 
Or if you aren't too fussy about quality the photo filters sold to put
rainbow stars on disco lights or on eBay. Astronomy magazines often have
adverts for slightly better than average gratings for eyepieces.

 
That means the time to get a sampling of the spectrum is multiplied
by the integration interval.  If, instead, you could get "quick peeks"
at each wavelength "quickly", and the more precise integration "later",
you have more data to work with, sooner.
 
[This is the approach I have historically taken with data acquisition
as it lets me trade response time for resolution, dynamically]
 

resolution can be as coarse or as fine as you like and algorithms can
work out the visual perception of line spectra (if that is what you
need).
>
The same hardware could be used for an expensive high-resolution device
or a cheap and cheerful version - the software and the time to reach a

 
"cheerful"?

 
UK alliterative saying.
I guess it doesn't translate into USAian too well.

 

steady reading (longer integration period for lower 'noise') being the
only real differences.

 
Figure out how much resolution you need before starting out.
 
A shovelware DVD at glancing incidence can resolve the absorption lines
in the suns spectrum if you do it just right. You look down onto the
disk with the sun at a very shallow angle to the surface. Don't look at
the reflection of the sun - only at the very dispersed spectrum.
 
The spectrum obtained with this simple kit is impressively high
resolution. It will also have various funny organic dye lines in with a
modern writeable one.
 
You really want aluminised media for this trick.

...or the transparent disc used to protect the end of a 'cake' of CDRs.

If you put your nose into the hole in the middle and shut one eye, it
displays a good spectrum.. I once had a collection of eminent people all
sat around a table doing this at a coffee morning in the Bath Royal
Literary and Scientific Institution.


--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk