Re: Open source Hamamatsu-based spectrometer
AlexeyD wrote:
rf-design wrote:
To measure spectral sensitivity of sensors a direct usage of a grating seems to be more useful because you get all wavelengths at one time.
Really? And just how you will ensure the same light levels for each band at each location projected to the sensor?
First of all I am not an expert and learn on the base of my education.
Calibration won't help you much there.
Calibration is the key to put an accuracy number on every nm of the spectrum. The calibration is a chain of uncertainity. It start for shure with the light source.
Light source themself is complicated because flash temperature is time dependend. Next issue is the filtering of the encapsulation.
Besides if you do it without lens (to take the lens out of the path and measure sensor spectral response directly) you will need a very precise alignment of the grating or calibration of sensor response to account for unevenness.
Plane focus accuracy of the colliminating grating reduce the spectral resolution. A 100mm focal length provide enough pixels.
It is impossible to use integrating sphere to diffuse the light and make illumination being photographed even without yet another calibration that is fairly tricky. And the last, I am not sure how exactly in that setup you will determine precise location of each band
There are atomic lines which are used as calibration.
- using just grating without controlling output slit is quite imprecise (very dependent on the falling angle) so yet another alignment and calibration is needed.
So all of this adding up, you will end up with a very tricky setup - it will be very hard to maintain consistency of the results.
There are other tricky solutions outside:
https://en.wikipedia.org/wiki/Grism
http://www.ebay.com/itm/132132416869
The setup with monochromator is very simple and precise, does not require any complicated calibrations to achieve precise and repeatable results and has very few variables to maintain (the most important one - unevenness of light is catered for by spectral measurements).
This is an example of the spectral sensitivity curves taken with this setup

Do you derive an error enclosure?