What Narrowband / lines filter (O-III, H-beta, H-alpha, S-II) can improve the results of my Canon DSLR with APS-C Sensor?

If you want to create absolutely beautiful color photos of bright deep sky objects (entry level) and wish to work with sophisticated techniques of Astrophotography (and the correct tracking), then your camera is ideal. For advanced working with long exposure times, i.e. with narrowband emission line filters, the DSLR is less suitable.

The reason is partly in the manufacturer’s narrow cut filter that is installed before the camera’s sensor only allows some of the main wavelengths (H-alpha and S II) to penetrate by a fraction over the prolonged exposure time.

Even if this limitation was lifted by conversion to a suitable astro cut filter, which lets through red, colour CCD sensors for photography with narrowband line filters are not ideally suitable as only every fourth pixel is addressing that wavelength.

Cameras (s/w cooled Astro CCD cameras) are already available for exposure times in this tight line area allowing exposure for many minutes, e.g. 200mm telescope diameter with at least 20 min exposure per wavelength / or filter. A DSLR camera would need several times more exposure time, and the resolution is then only one-fourth of the sensor pixels. Also a lot of noise is formed due to sensor warming (even with the best current cameras) and then noise reduction of the camera will strike so hard that the images start to become unusable. With in-camera noise reduction disabled noise in the image will be significant.

Furthermore, in many colour CCD sensors the narrowband lines leak into other colour channels so that these images then brightly colourful. So it makes sense for pure Astro CCD cameras to use monochrome sensors and cooled to allow extremely long exposure times.

This recommendation applies to the current DSLR development in 2016. It is foreseeable that the sensitivity and noise reduction is improving steadily in DSLR cameras. Cameras are also announced where by the shifting of pixel rows the loss of resolution can be reduced (e.g. Pentax K-1). It is moving more and more intelligence into the (CMOS) chip of DSLR cameras. Nevertheless, the monochrome, cooled Astro CCD cameras cannot be replaced by DSLR cameras for the foreseeable future.

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