CLS light pollution filter

[acarleton]

Hi all

one of my main goals of astrophotography is to shoot galaxies, a tough subject i know. I live in northern Sydney so i have quite a bit of light pollution. i was thinking of getting a CLS filter for my 600d EOS camera (attached to an f4 10" newt).
http://www.bintel.com.au/Astrophotography/Filters/Astronomik-CLS--br--EOS-Clip-/852/productview.aspx
i was wondering, how effective are these? will i be able to take photos of magnitude 10 objects with it? will it allow me to have a dark background? or am i doomed with my location.
i have heard that if you have an unmodded DSLR you will get some strange colouring, a blue tint. can this be overcome by shooting with RGB filters?

and finally, are narrow band filters useless for galaxies? i assume that due to the redshift, more distant galaxies will have their light filtered out with these, but are they appropriate for closer Messier, Caldwell and NGC objects?

[cometcatcher]

The CLS doesn't perform as well on galaxies as it does with nebula but if your LP is bad it may still help some. Hard to say how much.

You may not have a blue tint if your LP is from orange sodium lights.

Narrow band filters are mainly for nebula. Galaxies have too wide a bandwidth to work effectively with them.

I think DGM make a galaxy filter. The effect is mild so I wouldn't expect too much from one.

[Marios]

Hi Mate

I wouldn't be to discouraged you can still shoot galaxies with a LP filter.
It will never be as clear and rich as shooting from a Dark site without a filter, however there are many examples on the web of impressive results.

Here is one guys page note the filter type used:
http://cs.astronomy.com/asy/m/galaxies/445908.aspx
http://stargazerslounge.com/topic/182675-m51-l-rgb-cls-final-image/

There are many competing LP filters the CLS and CLS-CCD by Astronomics differ slightly were the CCD version cuts out just after the HA point.
This results in the rest of the useless interfering IR spectrum being completely blocked. The CCD is best used with full spectrum modified DSLR and CCD cameras.
The CLS is good for none modified DSLR which still retain there IR blocking factory filter. Both these filters will cause color shift regardless if the camera is modified or not.
This shift can be adjusted in post processing and also by taking a custom white balance.

The other very popular LP filter is the IDAS Hutech DS1 filter, similar to the CCD in spectrum coverage except for a few variations. These variations help with the color balance and hence this filter is widely regarded for good color balance.

PS. RGB filters are for Mono CCD cameras not DSLR, your camera already has a bayer system to handle color.

[Andy Walters]

Hi Aiden,
if you shoot a custom white balance on a grey card, and save it, that will bring your jpegs back to normal colour. Doesn't matter for raw, but looks funny (bluer) on screen.
Andy.