This filter is suitable for photographing nebulae from light-polluted areas, but also from places with dark skies. The contrasts between objects that glow in the light of the OIII spectral line (501 nm) and the sky background are greatly enhanced.
Due to the narrow half-width and high transmission in the OIII line, the filter achieves a significantly greater contrast increase than broadband filters. The half-width of 12nm is optimally matched to the use of typical CCD and CMOS sensors.
Even in large cities, images taken with cooled CCD cameras are usually limited by dark current. Therefore, further suppression of the sky background by lower half-widths does not reveal any more details in the object. Compared to very narrow-band filters, the 12 nm filter has the advantage that you can usually find tracking stars for almost all cameras with built-in tracking sensors.
The new MFR coating technology makes it possible to use the filter on all instruments up to an aperture ratio of f/3.
Difference between Astronomik 12nm, 6nm and 4nm Filters
The choice between 12nm, 6nm and 4nm half-width depends on your imaging conditions and your camera type. There is no universally ‘best’ option – each half-width serves a specific purpose.
The 12nm Astronomik narrow-band emission line filters are optimised for use with system cameras featuring CMOS sensors. They are also a good choice for CCD cameras with normal or high dark current. The 12nm filters are also the preferred choice for cameras with an integrated tracking sensor, as they show more guide stars compared to filters with a 6nm or 4nm half-width.
The 12nm filters offer the most affordable entry point into imaging with narrow-band emission line filters. Generally, the background signal in images taken on the outskirts of a town or in a location with a dark sky is limited by the sensor’s dark current rather than by light pollution. Further suppression of the sky background by reducing the half-width therefore does not reveal any additional details of the object.
Please note: In principle, all camera lenses can be used with the Clip-Filter - i.e. Canon EF lenses or camera lenses from other third party manufacturers such as Sigma, Tamron, Tokina, Walimex etc. However, the use of clip-filters with Canon EF-S lenses is NOT possible!
A bit of help with your selection:
- As a first filter, we recommend the Astronomik CLS filter. This filter suppresses artificial light pollution and natural airglow. By using this filter you get a dark-sky background and can therefore use much longer exposure times to make fainter objects visible. The filter is optimised in such a way that objects are reproduced in their natural colours. Important: the simple CLS filter has no built-in IR-blocking. Therefore you will need the CLS-CCD filter for an astro-modified camera!
- A good choice for working in locations with really heavy light pollution is the Astronomik UHC filter. The transmission curve of this filter only allows the light of the H-beta, OIII, H-alpha and SII lines to pass through. The background suppression is significantly stronger than with the CLS, however this filter works only for gas nebulae! Star clusters and galaxies are largely filtered out.
- For a more in-depth introduction to astrophotography, we recommend the OIII, H-alpha and SII emission lines filters, available with full width at half maximum of 6nm or 12nm. With these filters you can create detailed images of faint objects even from locations with extreme light pollution and a full Moon high above in the sky. Images in these narrow emission lines are not naturally coloured.
- For the owners of astro-modified cameras we offer the Astronomik OWB filter: OWB stands for "original white balance". The filter corrects the displaced colour reproduction of a converted camera so that it can also be used for normal every-day photography, without having to revise every image on the computer.
