Rgb filters.....

[TheShape]

So today I went to rvo to look at a scope and mount. Not in stock so hopefully gonna order next week for Christmas. One thing though that came out in conversation at the shop was the use of filters for Astrophotography. The guy in the shop says, I don't need a filter set unless my imaging camera in mono. I didn't want to question his authority as I'm a newbie. I thought filters were used to bring out the different colours in nebula etc. The way he explained was they're only used if the imaging camera is a mono one. Who's right? And are they necessary! 

 

[ollypenrice]

All electronic sensors are mono. Some have a matrix (usually a Bayer matrix) of colour filters placed over them at the production stage. These are called One Shot Colour sensors. In this case each light sensitive pixel has its own colour filter in front of it. In the Bayer system this is a repeating pattern of red, green, green, blue filters. The use of two green filters to every one in blue and red is to do with terrestrial photography and is hard to justify in the case of astrophotography. It isn't fatal in AP but it makes no sense that I can see.

It's important to understand what a filter does. A green filter, for instance, does not 'turn all light green.' It simply blocks red and blue. A blue filter blocks red and green, etc.

Those who use a mono chip without a colour matrix in front of it use filters, in turn, to record red, then green, then blue light on every pixel in successive images. These are later combined to make a colour image in much the same way as the camera software of a one shot colour camera does.

So you absoloutely do not need colour filters if you have a one shot colour chip. You already have the colour filters in place. You would shoot yourself in the foot, because if you put a green filter in front of a one shot colour chip, you would allow the green filters on your matirix to work but you would prevent your blue and red ones from seeing anything!

I'm a staunch advocate of the mono camera over the one shot colour for astronomy but that's for a different discussion.

Olly

[D4N]

You can use filters that increase contrast with a colour camera but as Olly says it would be a waste of time using RGB filters with a colour camera.

If you live in a light polluted area a filter would be recommended to help reduce the skyglow.

[TheShape]

Thanks. It will be an unmodded canon 450d.....to start with anyway. The filter you mention D4N, I assume you mean a simple 'light pollution' filter like this one so below. 

http://www.rothervalleyoptics.co.uk/skywatcher-light-pollution-filter-125.html

[D4N]

I don't know how well the Skywatcher filter performs for imaging.  With imaging it is important that the filters have coatings that prevent reflections.

I have a Baader UHC-S filter, I used to use it for imaging when I used a DSLR but now I just use it for visual.