When we use one shot colour cameras like DSLRs, coulour is captured. You only need to enhance it by software. Optical Filters are not used to capture colour with Oneshot colour cameras.
With DSLRs ,Generally filters used only to tackle light pollution and for enhancing nebulosity as incase of H-Beta filters for Horsehead like Nebula.
In case of Monochrome CCD cameras, RGB filters are used to capture 3-channel colours.
I have addeed another image of M42, using 19 subframes of 180 sec each (Total 57 minutes) captured using Baader LPR filter.
The total duration of earlier shot was only 28 minutes, un- filtered
Frankly I do not think the difference in quality of final product is that obvious, inspite of doubling the duration, in the second image.
Kochu/21-2-10
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http://www.singastro.org/album_showpage.php?pic_id=1148
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