Baader PlanetariumSemi-APO Filter 2" FSAPO-2

I bought this filter to use with my 6" achromatic refractor after reading other reviews around the net stating that it reduced chromatic aberration (CA) without affecting natural color like some other filters.I've tried the filter several times while viewing Jupiter, and it does cut down a lot of the CA, but does this at the expenses of dimming the object too much at higher magnifications. I found that I liked the views of Jupiter with CA better than the views with the filter. I also felt that I was seeing more detail on the planet without the filter and that the filter caused somewhat of a loss of contrast.Considering the cost of this filter I feel that the value just isn't there and I regret purchasing it.

I tried this on a f/5 and a f/6.5 refractor, and it really didn't didn't reduce the CA as much as some people have reported. Now I must also say that people have different sensitivities to CA and also CA reduction filters, so it could work for you. Doesn't change the color of the object like a long pass 495 does, or a yellow #11

Great filter, beaware it dims your field as well

This is a great filter for owners of longer f-ratio achromats, like the 6" f8, 120mm f8.3, or 4" f9-10. Removing the haze of unfocused violet light sharpens up lunar and planetary detail quite a bit, while the color cast is closer to neutral than in some competing filters (not to mention a traditional plain yellow filter). I have various Baader filters and the optical and physical quality is always top-notch. My only complaint is that the labels on the filters are silver, and nearly impossible to read under dim light. The labels should really be white.....I've made tiny tape labels to identify mine while observing.This filter is especially fantastic for daytime observing of the Moon and Venus. In addition to cleaning up the chromatic aberration the slight yellow tint darkens the blue sky, and increases contrast dramatically.If you have a faster scope, like f5-f6.5, it will have more chromatic aberration. This filter will still help but some of the unfocused light will still pass through. Baader makes another filter that's stronger - I think it's called the Contrast Booster - that would probably work better on such scopes but adds more of a yellow tint.

This filter may work for long tube F8 or higher refractors. I bought one for e my AR102 F6.9 doublet by explore scientific in hopes of making the scope work better for photography. On this scope the filter did little to the overblown blue glow around stars on long exposures. I tried shots of nebula and had the same issues with all the stars around the shot. While it did cut the blue glow some. this is not a fix for a short tube refractor. Tried it on my Celestron d70 I bought for a guide scope and solar scope. It did not work on that scope either.