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
