Saturday, July 25, 2015


On the evening of July 14, 2015 I took a picture of Pluto to celebrate the flyby of Pluto by NASA's New Horizons spacecraft. But, there was a problem: I couldn't find it!

Pluto is very small, and also very dim. It is typically around 14th magnitude, which is about 128 times dimmer than the human eye can see in Earth's darkest skies. It's not even visible in most amateur scopes, outside of using long-exposure photography. In addition, the part of the sky that Pluto is currently located in is along part of the Milky Way. How was I to locate such a small, dim object among all of those stars?

Plan A was to use my various planetarium programs to find reference stars that would aid in locating Pluto. That failed because none of them had enough stars in their databases to account for everything I was seeing. I made an educated guess (which I discovered was correct), but there was no way to tell for sure until I could implement Plan B.

Plan B was to use a technique similar to that used by Pluto's discoverer, Clyde W. Tombaugh. Tombaugh worked for the Lowell Observatory in the 1920s and 1930s. He would select a part of the sky and take a picture of it with the observatory's 13-inch astrograph (a telescope designed for photography). A few nights later he'd take another picture of the same area. He then used a blink comparator to look for differences between the photographs. Objects that stayed in the same position were stars, but anything that moved was a comet, asteroid, or a planet.

I took my second set of images on the night of July 24, 2015. After processing and lining up the images I was able to see that my suspect Pluto was, in fact, the real thing! The animated GIF below shows Pluto's position on the two nights:

Pluto! Click on the image for a larger view.
To further illustrate how inconspicuous Pluto is, I put together this movie from the July 14th image:

So, there you have it. A mundane little dot moving among a sea of other dots. Who knew what a beautiful little world Pluto would turn out to be?

Public domain image courtesy of NASA and Wikimedia Commons.

Waxing Moon, July 24, 2015

The Moon, July 24, 2015; ST80 w/CB on Vixen SP
38 images, ISO-100, 1/160 second exposures

This is my first attempt at imaging the Moon using the new Baader Contrast Booster filter. When I image the Moon with the ST80, I generally use the stop-down adapter that's built into the dust cap. This reduces chromatic aberration, yielding a sharper image with a less-pronounced red/blue halo surrounding the Moon. The disadvantage to using the adapter is that it greatly reduces the telescope's aperture, which reduces the amount of detail in the image.

This image was made without using the stop-down adapter. It was stacked in RegiStax 5.1 and processed in Photoshop CS6. There were some color anomalies, but I hid them by slightly desaturating the image and adjusting the curves a bit. The ST80 certainly doesn't capture the Moon's color characteristics as well as the Epsilon 200, but overall I'm pleased with what the filter can do.

Next, I may try using a Barlow to get a closer view.

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.