It protects your sensor from dust build-up during long exposures.
How this filter works: Artificial lighting such as mercury vapour lamps, both high & low pressure sodium vapour lights and unwanted natural light caused by neutral oxygen emission in our atmosphere (skyglow) are almost completely suppressed by the SkyTech CLS filter.
The filter selectively allows light from deepsky objects through, with high transmission of ionised oxygen O-III (496nm & 500nm), Hydrogen Beta / N-beta (486nm), N-II(654nm and 658nm), H-alpha(656nm) and S-II(672nm).
By selectively blocking light pollution and transmitting these desirable wavelengths, the contrast and detail of deepsky objects is greatly enhanced.
Precision laser-cut housing.
Schott glass substrate material with precision polish.
Glass thickness 1.0 mm.
Surface Quality: 60/40 (Refer to MIL-O-13830)
Fine-optically polished to ensure accurate 1/4 wavefront and < 30 sec parallelism over both surfaces
95% transmission of main nebula emission lines (i.e. Ha 656nm, OIII 496nm & 500nm, SII 672nm and H-beta 486nm).
0.1% transmission of off-band, specifically the major emission lines of artificial light pollution (i.e. Na 589nm, Hg 435nm and 578nm).
Dichroic Filter Coatings:
Multi-layer anti-reflection coating (AR Coat).
Special high homogeneity coating process with electron-beam gun evaporation and Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL (central wavelength) no deviation with temperature change.
NOTE: Filter fit can be adjusted to sit snugly in your APS-C sized EOS. Instructions on the adjustment can be found here