Wow, thanks Richard, that’s incredibly helpful!
I’ve got some ebay alerts set up for PR devices, as well as Jetis, so it sounds
like i’ll just be waiting a bit longer for the right one to come along.
Until then I’ve got a KM CA-210 on the way in the mail to play with...
Definitely not afraid of the serial port devices— it was kind of recently that
I realized how usb devices are constantly dropping off the map because of
unsupported drivers in new OSs, but serial devices just keep trucking along...
On Feb 18, 2020 at 5:40 PM, <Richard Kirk
(mailto:dmarc-noreply@xxxxxxxxxxxxx)> wrote:
Quick answer… There are lots of spectrometers that use fibre-optics in this
sort of price bracket. They are sometimes the spectrometer part of more
complex instruments. The really good instruments are large because you can
only get good contract ratios with a large black internal void where all the
light that ought not to be there can get lost. Without this, you have a
spectrometer the size of a sugar cube which can make perfectly good
measurements but any scattered light may come back somehow, and you have to
find out exactly how. This is not fatal: you can correct for higher order
reflections from the grating, and other such things. You can also calibrate
using standard light sources. I worked on the Truelight projector probe,
which is one of these gadgets. The Hamamatsu micro-spectrometers are very
good and robust gadgets, but even they have to be calibrated in power and
wavelength. Another expense is often to add some light collection device on
the front so you can point it at a display and make a reliable measurement.
Even the good spectrometers you can get are generally calibrated from NIST or
NPL or other national body sources from a bolometer. A bolometer is a gadget
that can tell you exactly how much power you are getting from your light, by
turning it into heat; but these are usually really inefficient, so they are
used to calibrate the spectrometers in watts per steradian, and a standard
spectral lamp is used to calibrate the wavelengths in nm (I used a Helium
lamp). Conclusion: there is a reason why these things are cheap. They have
probably skimped on the light collection and the calibration. Adding these
adds to the price. I do not know this particular gadget but I have seen
several similar ones. If they only quote one figure (6nm) then this is very
suspicious. You could have a 1D light detector with 256K elements to image
visible light from 400nm to 700 nm. This will give you a resolution of nearly
1nm per photosite if you could spread your spectrum exactly. But most gadgets
like that manage about 10 nm resolution. They can work quite well on that if
they are properly calibrated. If I had to give a recommendation, I would
suggest looking for a second-hand Photo Research spectrometer. I have an
ancient PR-650 that is thirty years old and still working. The old ones can
be a bit of a pig to talk to over a serial port, but the spectrometer is a
big piece of optics. If you are lucky, you may find one in decent condition
for a couple of thousand. Good luck! Richard Kirk
