Fighting light pollution with Astronomik CLS and CLS-CCD filters


Astronomik CLS and CLS-CCD are quite bright filters that are designed to cut light pollution and sky glow. Both filters are available in different sized including Canon Clip filter that mounts inside the DSLR body. They are bit brighter than Baader UHC-S and similar UHC filters. They pass [O III], H-beta, H-alpha, [S II] bands in which emission nebulas glow. They don't pass bands in which street lights glow. CLS-CCD has an IR cut just after [S II], while CLS just keeps the transmission further in the IR. Those filters can be used visually, but they will give most of themselves in DS imaging.

Astronomik CLS-CCD

In astrophotography they can be used with colour and mono cams. Broad transmission bands limit colour balance changes (although it will be changed in some extent). For DSLR the CLS version seems to be recommended, while mono cameras should use CLS-CCD to avoid IR refraction on bright f-ratios and other similar problems.

For with/without comparison you may check stargazerslounge, or for example Markarian test (also from SGL):

Light pollution cut-out comparison
For high pressure sodium lamps that are oftenly used in cities CLS performance should be nearly equal to the UHC type filters:
HPS lamp vs filters - CLS-CCD and UHC-S

CLS and CLS-CCD have slightly different spectral performance. Astronomik website gives such figures:

Comment article