Can diffraction gratings be used for shots in adverse conditions (rush, rain, quick move, speed) ?
This is a shot taken on the fly while driving at 60km/h [37 mph]).
On this shot, 3 types of “classic” spectrum :
1- A continuous spectrum (light generated from a solid – here a filament). Similar spectrums can be obtained from the moon.
2- A spectrum with emission lines (light bars). Example of a mercury-vapor lamp – typical from white light streetlights, sometimes also from low consumption lamps.
3- A spectrum with absorption lines (dark streaks in the color gradient). Here the famous sodium double line of orange streetlights (not that obvious on this shot).
The imaging device used is a mobile phone with a 5 megapixels CCD without specific settings except flash disabled.
Let’s consider another shot from this series :
On this shot, two distinct light sources.
Let’s isolate each spectrum :
« Orange » source
« White » source
We have here 2 spectrums potentially exploitable for analysis.
ANALYSIS and CHARACTERIZATION
By comparing to an easy to find and known reference (in town or in the countryside) : the sodium !
From this reference spectrum, we can infer the second source lines wavelength. This analysis is precise enough to confirm the the correct matching with a public light bulb !
So, to the question: “Can diffraction gratings be used for shots in adverse conditions (rain, movement, speed, rush…)”, the answer is definitely :
YES
PS : This analysis cannot be done with three mouse clicks !
Additional information: The wavelength range recorded extends from 400 to 680 nm while the MAZDA spectrum is from 380 to 720nm. The recorded spectrum is clearly narrow.
Two factors explain this:
1 – The material used for the grating (400nm to 1000nm)
2 – The CCD characteristics from the camera.
Some CCD sensitivity is more developed in the near infrared (780nm to 1400 nm) as the ones found with B&W camera. Color cameras generally have an IR filter.