Hi John,
I so far have used 4 different types of Light Pollution filters for imaging.
No 1.
A very economic Antares 1.25 inch Light Polution filter. I started off using this and got some great results using my UnModded Canon 350d, taking images at prime focus through My 6 inch and 11 inch scopes. It certainly helped, and I still have it, mainly for visual use for my 1.25 inch DS viewing.
No2.
Interest in wider field imaging using my camera lenses, resulted in purchasing an Astronomik EOS CLS filter. The beauty about this was that it sits between the lens and the camera (you have to ensure the type you get will fit the camera), so I could use any of my Camera Lenses (with the exception of the stock EF-S lens that came with the Canon Camera), Plus using it with my scopes. Without it, a 2 minute exposure using a 90mm lens at F2.8 resulted in a totally Red sky. With it, you could clearly see the difference, however it gave a Cyan colourcast to the image when viewing. This could be overcome by adjusting the colour balance of the camera prior to shooting or in post processing. The end result was that it did make a big difference.
No 3.
A Baader 2 inch UHC-S Filter. This, I bought to accomodate my 2 inch eyepieces for visual observing, and it did make a huge difference. The Ring Nebula, for example "jumped out" due to the extra contrast. When I got my Modded 350D (IR filter Removal), I also used this for imaging and got happy results with it. However, it does allow some IR frequencies to pass through, therefore star bloating could be an issue, during Photography. The colour balance was pretty good though using my recently acquired Modded Canon 350D, but had to be tweaked also.
No 4:
Again being limited to using the Baader 2 inch in my scopes and wanting to also have something that I could use with my Lenses, I decided to get the Astronoimk EOS
CCD CLS Filter. The difference in this from that mentioned in "No.2" was that it
also blocks IR ( a neccesity when the IR Filter is removed from the Camera), which could lead to bloated stars. I haven't got much of an opportunity to experiment with this one yet, however, I did point the Camera (Piggybacked using a 90mm Tamron Lens) at Vega for an hour with this filter attached and was very happy with the results. As you can imagine the removal of the IR filter in the Camera results in much more Red being registered, however, the filter compensates for some of it, while adjusting the camera colour balance with the filter in place, can compensate for the rest, while still allowing the necessary frequencies for nebulosity imaging through.
Just going by my experiences to date and limited exposure to only the four mentioned above, all I can advise is the following:
1. If using an
UnModded Camera such as the stock 350D =
Standard Astronomik EOS CLS. Gives a cyan colour cast, unless you adjust colour balance. However, excellent results when done.
2.
Baader UHC-S Filter - Great for
Visual (well it was looking through my 11 inch scope), and also good results using my "IR Filter Removed Canon 350D". However, I used the 2 inch version, therefore limiting myself to my scopes. Clolour Balance adjustment required, but not as much for the Modded Camera.
3.
Modded IR Filter Removed 350D =
Astronomik EOS CCD CLS Filter. This also blocks IR, thus heping to reduce star bloat. Initial tests have been very very encouraging, however, as it is a new arrival I have yet to put it through proper paces. Still an element of Colour Balance adjustment due to the use of the "IR Filter removed 350D".
Again, this is only my only experience to date, I am sure more experienced imagers on the boards, will be able to advise you more, due to their experiences.
Hope it is of use.
Beat regards
Steve
www.flickr.com/steveroche
  