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Explore Scientific's 12-inch Truss Tube Dobsonian

This telescope offers top-notch construction and high-quality optics, and is easy to set up and use, as well.
ASYER1117_01
Explore Scientific’s 12-inch Truss Tube Dobsonian offers a large aperture at a reasonable cost.
Mike Reynolds
The Dobsonian, John Dobson’s sidewalk telescope mount design more commonly referred to as a Dob, has evolved significantly since its first commercial introduction in the 1980s. Many of us remember the blue tube Coulter Optical Dobsonian telescopes, the first of which contained a 13.1-inch primary mirror.

Soon, amateur telescope makers and companies began producing larger and more innovative Dobs. The simplicity of the mount, coupled with a large mirror, made them popular telescopes. The Dob rage brought on what many referred to as “aperture fever.”

The basic Dobsonian mount carries a Newtonian reflector with its concave primary mirror and flat secondary mirror mounted at a 45° angle to the primary. As the Dob evolved over the years, innovations such as shorter focal lengths for the big scopes, primary mirror cooling fans, equatorial tracking tables (an accessory that serves as a motor drive), and numerous others appeared.

Truss tube Dobs were also one of these early innovations, brought on by need and by mirror-size evolution. As the primaries became larger, solid tubes of either cardboard concrete column tubing or metal became impractical due to weight. This led to the truss tube: a set of rigid poles to connect the lower part of the Dob — referred to as the rocker box, which contains the primary mirror — to the Dob’s upper cage, which holds the secondary mirror and focuser. This design, and the use of innovative connectors, means the telescope quickly disassembles into the rocker box, the mirror box, the secondary cage assembly, and the truss tubes.

Opening it up
Explore Scientific, known for its apochromatic refractors and wide-field eyepieces, has entered the market with three new Dobsonian telescopes. The trio features a number of traits standard to most Dobs along with a few surprises.

The Explore Scientific 12-inch Truss Tube Dobsonian arrived in one box. This was the first surprise; previously reviewed Dobs have always needed at least two boxes. I appreciated that the included user manual was well-written, and even contained pictures!

Assembly of the telescope was easy, and this would hold true even for a beginner. I found the construction solid, from the mirror box to the secondary mirror cage. The finishes appear nice and should last through many an observing session. The weight of the 12-inch components is reasonable, and they easily fit into my Camry’s back seat or trunk.
Info
The next surprise was the collimation tool for the mirror. Collimation (the alignment of a telescope’s optics) is usually tedious or takes two people. Explore Scientific has designeda system so the user can employ the collimation tool, a rod that lets you collimate the scope from the focuser. Usually you are back and forth to the rear of the telescope, or telling someone, “No, the other screw; tighten not loosen.” What a great innovation!

The focuser is a 2" twospeed (10-to-1 reduction) model. The finder included is a red dot finder. I prefer an optical finder scope on my Dobs, but the red dot finder is adequate and reduces the secondary mirror cage’s weight. Yet if that weight becomes an issue, or you want to use one of these heavy wide-angle eyepieces, Explore has included threaded counterweights. This was another unexpected surprise.

You should know that no eyepieces are included; most purchasers of scopes this large will already have at least one eyepiece. However, if this is your first telescope, make certain you order an eyepiece or two with it. I would suggest a wide-field 25mm as a starter. You might also want an 18mm for a little higher magnification, or a longer focal length eyepiece for a wider field of view and lower power.

Taking it for a spin
Under the night sky, the telescope performed well. It was easy to move around to its final observing spot. Once at the eyepiece, I also found it easy to adjust the tube’s position while observing. The focuser works well. I always appreciate the 10-to-1 reduction. It allows for getting the focus just right, especially at higher magnifications. And the focuser held my fairly heavy wide-angle eyepiece with no slippage.
ASYER1117_02
The Dob’s focuser accommodates 2" eyepieces and offers two focusing speeds.
Mike Reynolds
There are several general observational tests I do on all telescopes. Even though I was expecting no color issues, I like to test telescopes on the Full Moon. I detected no color issues, but our satellite was overwhelmingly bright, so I had to use a filter. The Explore Dob also performed nicely on the waning crescent Moon, providing a crisp image.

On a good night, a contrast between two telescopes can be established. My yardstick is a tough one here; I compare Dobsonians to my personal 18-inch f/6 Dob, a high-quality one that used to belong to a close friend. The Explore Dob views were excellent; I pushed the telescope to 90x with a 17mm eyepiece and then to 127x with a 12mm with no problems and a great image. I did try a 2x Barlow lens, but found my local sky conditions were not good enough to give a fair test. I noted that the image of Jupiter was OK, but not as good as at 127x.

Deep-sky objects were excellent, from the brighter ones like the Orion Nebula (M42) to some of the season’s dimmer and more elusive targets. I also spent some time looking at double stars. One of my favorites this time of year is Albireo (Beta [β] Cygni) because it’s easy to see and colorful.
ASYER1117_03
The secondary cage and focuser fit inside the Dob’s rocker box for storage and transportation.
Mike Reynolds
Conclusions
All in all, I was pleased with the telescope’s performance. I did not note any visual issues like coma, astigmatism, or other distortions.

Many of us Apollo program-era kids considered ourselves fortunate if we had an opportunity to look through someone’s 12.5-inch reflector. And you were quite advanced if you owned an 8-inch Newtonian reflector. Today, if you catch aperture fever and want to see many of those subtle deep-sky object colors, faint wisps, and nebulosity, or if you want Jupiter to appear like you’ve never seen it in smaller scopes, a Dobsonian just might be for you. And Explore Scientific’s new trio of Dobsonian truss tube telescopes gives you a selection with excellent optical performance and great mechanical quality at good prices, with convenience of setup and use — just know that even the largest of these will eventually leave you wanting something bigger. In the meantime, explore as much of the night sky as you can with one of Explore Scientific’s fine new telescopes.
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