Baader Violet Multi-Band Filter
Baader Planetarium is a German manufacturer of planetarium equipment and telescope accessories. One product they recently offered is called a "Violet Multi-Band Filter". I purchased one through Astro-Physics for $30.00. It was designed as a type of nebula filter to reduce light pollution when observing deep sky objects. I was told a side benefit is that the filter can be used on the Moon and planets to reduce glare and increase contrast. The filter looks to be of very high quality. Baader grinds and polishes each filter to insure they are optically flat. Some of the cheaper colored filters on the market are punched out of a sheet of glass with what looks like a cookie cutter. The filter arrived with an instruction sheet with nice graphs apparently showing how superior this filter is. Unfortunately it is written in German and I'm a little rusty in that language.
I first tried the filter on the Orion Nebula. I could detect a very slight increase in contrast but it made the whole view a little dimmer. The effect was the same on all deep sky objects I looked at. For blocking light pollution, I don't think this filter works very well. Perhaps the light pollution in my neighborhood is of a different type than in Germany.
I next used the filter on Jupiter and am happy to say this filter worked nicely. It had the same effect as my neutral density filter but the view seemed a little sharper. As the "Violet Multi-Band" name suggests, the filter imparts a slight blue tone to the image. I compared the views through the Baader filter and a light blue Brandon filter. The amount of planetary detail I observed was the same but the Baader filter seemed to give a more pleasing view.
This filter really works well on the Moon. Observing the Moon without some type of filter is difficult. The view is so bright it hurts to look at it! The Baader unit has replaced the regular neutral density filter I carry in my eyepiece case. I think the view is crisper than my other filters and it seems to block just enough light to make observing for long periods of time enjoyable.
Thirty dollars is quite a bit of money to pay for a single filter. It is two to three times the cost of a cheaper colored filter and you will not see three times the detail on the Moon. I would recommend the Baader filter for the more experienced lunar observers in the club. A beginner may find a standard neutral density filter works just as well for much less money - and I just happen to have one for sale!Published in the February 2002 issue of the NightTimes