Monday, July 20, 2015

Baader Contrast Booster

This post is fairly long, so here are the pictures. I'll meet you on the other side!

Messier 8, the Lagoon Nebula; ST80 w/Baader CB on Vixen SP; Canon EOS Rebel T3; 11x120 @ ISO-3200

Messier 7, Ptolemy's Cluster; ST80 w/Baader CB on Vixen SP; Canon EOS Rebel T3; 32x60 @ ISO-3200

Back in February I purchased two new toys for my ST80/Vixen Super Polaris rig: a Baader Contrast Booster with IR-Cut filter, and an ADM dovetail saddle adapter. Family, clouds, weather, clouds, personal health, clouds, work, clouds and clouds prevented me from doing any astrophotography until mid-July.

The Vixen Super Polaris was the last mount of the Polaris line that was produced without a dovetail saddle. Personal budget limitations have prevented me from upgrading to a modern mount, but ADM Accessories makes an adapter within my price range. The VSAD-SP bolts to the top of the mount head. Two large, spring-loaded screws on the saddle grip the male dovetail bar very securely. Installing and removing the scope is very easy now. In addition, the telescope and camera can be properly balanced on the declination axis, which was impossible before because of the size of the scope and arrangement of the rings.

I'm always trying to find ways to get better images out of sub-par equipment. The ShortTube 80 is a great little scope for casual viewing, but the chromatic aberration inherent to fast achromats makes it unsuitable for imaging. A quality imaging scope is still outside of my price range for the foreseeable future, so I am trying to make the best with what I've got.

My research and experimentation led me to try the Baader Contrast Booster. The Contrast Booster filters out wavelengths on the extreme ends of the visible spectrum that are responsible for much of the blurring and halos caused by chromatic aberration. It also filters out wavelengths produced by common sources of light pollution.

I had the opportunity to try the filter visually against the Great Orion Nebula back in March. The moon was at 68% illumination and the nebula was about 30 degrees above the light-polluted horizon. Despite all of that, I could see a remarkable difference in contrast.

The two images above were made using the Baader Contrast Booster. The chromatic aberration, while not competely removed, was significantly reduced. This was a major improvement over my best results with the Orion SkyGlow Astrophotography Filter and the #15 yellow filter discussed in the Fixing Halos post.

The three following images illustrate the differences among the filters:

Baader Contrast Booster
Orion SkyGlow Astrophotography Filter
Yellow #15
The stars in the Contrast Booster image are larger, but that may be due to the fact that it was shot at ISO-3200 versus ISO-800 for the other two. The important thing to note is that the halos are confined to a tight ring around the stars.

The image of the Lagoon Nebula at the top of the post was processed without attempting to remove the effects of chromatic aberration. I applied the Color Layer technique to the image of Messier 7 to reduce an overall purple hue that was likely the result of all of those bright stars.

I was concerned that the Contrast Booster might cut out too much blue from the images. Pure blue hues are not common in astroimages. The best example that I can think of is Messier 20, the Trifid Nebula. This nebula presents a striking contrast between a red emission region and blue reflection region. The image of M20 below was compiled from only five subs, so it is fairly grainy. However, the blue came through the filter nicely:

Messier 20, the Trifid Nebula; ST80 w/Baader CB on Vixen SP; Canon EOS Rebel T3; 5x120 @ ISO-3200
I plan on doing more tests and reimaging more objects with the Baader Contrast Booster. So far, however, I think this filter brings the ST80 close to the performance of an ED refractor--at least as close as it can reasonably get.

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