Review: Third Planet Optics 6-inch f/6 Optical Tube Assembly

Credit: Third Planet Optics

We live in a golden age of telescope equipment. Just look around and you’ll find a quality piece of equipment at a reasonable price.

However, even I am amazed at the bargains out there. Take, for instance, this 6” f/6 OTA (optical tube assembly) from TPO (Third Planet Optics). It is available from a number of different web sites. You get the optical tube, 2-inch focuser, 6×30 finder, tube rings, and Vixen-style plate, all for $229. If you add up the prices of everything I listed after “optical tube” in the previous sentence, you can easily arrive at $200+ for these accessories alone.


A 6-inch telescope is often considered an ideal starting point for a serious amateur. It is large enough to show you the planets, the moon, and deep-sky objects like star clusters, nebulae and double stars, but it is not so large that it becomes unwieldy and cumbersome to transport. The sample I tested, purchased anonymously, has excellent optics and, at 14.5 lbs, fits well on a mid-sized mount like Celestron’s CG-5 or AVX.

I spent several nights with the telescope in July of 2020, both at public observing events, and with astronomy club members. I looked at Jupiter, Saturn, and deep-sky showpiece objects like the Ring and Dumbbell mebulas (M57 and M27), and globular clusters like M13 and M92. The major cloud bands and four moons of Jupiter were easily visible at even at low power, as were the rings of Saturn, as well as its largest moon Titan.

If you’re a beginner looking to buy one of these, I recommend it with enthusiasm. However, there are a couple of things you need to know. First, it is an optical tube only. You will need a sturdy astronomy-specific mount. Your photo tripod, no matter how sturdy it may appear, is not going to work. I recommend a mid-sized mount like the ones pictured. These mounts sell for anywhere from $600 – $900, so you will have to figure this into your purchase price. If you are an intermediate or advanced amateur, you likely already have such a mount.

Second, the eyepiece will not come to focus unless you use the supplied extension tube. Experienced astronomers know to use these tubes, but beginners might be baffled as to why nothing will focus. The reason is many telescopes these days are configured for cameras, which require a different focus point. Many manufacturers assume you are going to be taking pictures, not looking through the telescope. I have mixed feelings about this trend.

As long as you are aware of the issues described above, I cannot recommend this telescope enough. Note that this telescope may be found carrying a number of different brand names on its tube, including TPO, GSO, Orion, and others.

When I was a teenager in the 1980s, I took a job flipping burgers at a fast food restaurant to earn enough money to buy my first telescope. Coincidentally, it was a 6–inch reflector like the TPO. Factoring in inflation, I could have spent a lot more time observing, and less time in the burger joint, had a product like this been available back then. Luckily, you do not have this problem.

Good hunting with your new telescope!




About Ed Ting

Ed Ting is a well-known amateur astronomer. His work has appeared in Sky & Telescope, Night Sky, Skywatch, Amateur Astronomy, Discover, and Popular Mechanics magazines. His web site,, is a widely-read telescope review web site. He is a National Science Foundation Ambassador to Chile and a NASA Solar System Ambassador.

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