Sirius Optics MV1 comparison on M35
All achromatic refractors have problems focusing light of different wavelengths to the same point. This chromatic aberration causes images of bright objects to have colored halos (usually blue or violet) around them. Apochromatic refractors add additional glass elements to correct this, but they are much more expensive and beyond the budget of many amateur astronomers.
The Sirius Optics MV1 filter is designed to minimize blue halos around stars in achromatic refractors. MV stands for minus violet and it works by filtering out the blue/purple wavelengths of light. Technical details about the characteristics of this (and other) filters can be found on their site.
To review this filter, two images were taken of the open cluster M35. Both were 10 minute exposures on 35mm Elite Chrome 200. All images were taken at the prime focus of an Orion 120ST refractor - a 600mm f/5 instrument designed for widefield use. A JMI NGF-SE focuser was used in place of the stock focuser. Images were scanned on a Nikon Coolscan IV ED negative scanner with the exposure locked to give an accurate representation of the effects of the filter. Scanning was at 2900 dpi resulting in images of 3968 X 2648 pixels. Various views and sizes of these two images are presented here. With the exception of the final two images on this page, no adjustments other than sizing and cropping were done.
A similar set of exposures/comparison was done for M42 - The Orion Nebula.
Central portion of the images after sizing to 25 percent. Since the MV1 filters out blue light, it imparts a yellow cast to the photo. The filtered image is slightly darker as well. Blue halos are significantly reduced. |
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| Unfiltered image Click the image above to see the full-frame image |
Filtered image Click the image above to see the full-frame image |
Central portion of the full size, full resolution images. |
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| Unfiltered image | Filtered image |
Central portion of the images after sizing to 25 percent, color corrected and level adjusted. |
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| Unfiltered image | Filtered image |
Conclusion
This filter significantly reduces blue halos around bright objects both visually and
photographically.