William Optics 2" Minus violet Filter

For the achromatic refractor owners this product seems to be what you need to get rid of those blue halos around bright objects. In the image without the filter the brighter stars have a blue halo around then and in the other image they are almost eliminated.

The images are only color combined. Only dark frames have been applied to the original image. Each image is made up of a single 2 minute exposures for each color. The images above have some field rotation due to less than accurate polar alignment but you should be able to see the difference.

Visually the filter blocks out the blue halos around bright objects associated with achromats but at the cost of making images appear a bit more yellow.

If your telescope use is limited to visual observing, skip this add-on. On the other hand, if you're planning on attaching a camera to the scope, pick up the MV filter. Why do I say this? The filter blocks out some light and for visual use I want as much as the OTA can offer, blue halos or not. The camera can "see" more light over time so the absence of some doesn't bother me that much and my images can be adjusted for any color imbalance.

Image with the filter installed

Image without the filter installed