Measurement of the FWHM using the Sun as a light source


Optical setup: Sun => BF => SHG700 => IMX885

Configuration of the SHG700 f_c = 125 mm, _fim= 2000 mm, grating 2400 lpmm, IMX585
dispersion = 0.0471 A/pixel

The following images show the solar spectrum (without any filter), the spectrum transmitted by the blocking filter at normal incidence, and the spectrum transmitted with the filter tilted..



At normal incidence :
- The Center Wavelength of the BF is not centered on Ha.
- Oscillations are visible in the transmitted spectrum at normal incidence. Since these fringes disappear when the filter is tilted, their origin might be interferences building within the filter.

Note that such fringes were not visible with the IMX585 was used to measure an Heliostar BF. However, in that case, a spectro with a lower resolution was used:
../../Skywatcher/Heliostar100_C/Heliostar100-C_BF.html 

Transmission is the ratio between the solar spectrum light transmitted by the filter and the solar spectrum::




In the following curve, the dent on Ha is an artefact. It is the result of the presence of the dark Ha line combined with interpolation effects.


Noteworthy, the FWHM does not change significantly when the filter is tilted to be centered on Ha.