Today, Dobsonian Telescopes are as popular as any design of telescope on the market. Its not surprise why: They are easy to use, and they give the biggest ‘bang for your buck’- the most aperture for your telescope dollar.
But it wasn’t always this way. Times were that using a Dobsonian telescope was something that only true hardcore amatuer astronomers did. Using a Dob was the equivelant of a computer gamer overclocking the chips on his computer – something most people just couldn’t do despite the benefits it may reap. So why was this the case?
Dobsonians are credited to one Jon Dobson, who created the design to make telescopes easier – many folks did not like having to fuss with heavy equatorial mounts and tripods. So Dobson developed a simple “lazy susan” platform, put a large wood fork on that and stuck a reflector tube with some round hubs stuck on the sides that would let the tube pivot and “voila” you’ve got a simple mounted telescope! Thing is, Dobson invented the concept in the 50’s, and it wasn’t until very late in the 90’s or even the early 00’s that Dobsonians started to be popular.
So why didn’t “The Dob” catch on for decades? it certainly wasn’t ignored, but it definitately fell into the realm of simple equipment only used by hardcore users. What was the problem.
A small part was that they did not look like traditional telescopes. They tended to look like medieval cannons, not delicate optical instruments. But that was not the majority of the problem.
The main issue? Balance. You see the Dobs didn’t have anything that would secure the optical tube to the base and keep it from drifting off target. THe problem stems from the telescope tube being very light at one end (the open end) and very heavy at the other (where that thick, wide mirror sits.). There was no easy way for people to balance the instrument as the angle of aiming changed – the telescope might be balanced just fine at 30 degree from level, but not at 70 degrees and it would start to drift. Dob owners had dozens of hacks to maintain balance. Sliding weights, magnets (for steel tubes) and many other tricks, but they were obviously a bit to much for casual users so Dobs never took off. As a result, while there were a few specialty Dobsonian telescope makers the mainstream telescope manufacturers tended to put Dobsonians in their ‘other products offered’ category. The resulting dobsonians weren’t much to speak of – cardboard (sonotube) bodies, the lowest quality mirror they could get away with (large, but barely driffraction limited), secondary mirors held on with a cheap iron stem, etc. etc.
Somwhere around 1999 that changed. Orion Telescopes decided there was a potential market to mine if they could only solve these issues. The solution, as it turned out, was to simply use springs.
This is one of those things where you look at the solution and go “why didn’t I think of that?”. It seems pretty simple, and in fact many Dobsonian users tried different tricks, such as tying down the tube but the high-tension springs provided the pressure needed to keep the tube from drifting, but without making it too hard to move (thanks to some well-placed teflon pads on the base where the hubs meet). The development wasn’t always easy, legend has it that the Orion engineers ordered two of every spring in the Grainger catalog to see what worked. The result was what Orion referred to as the ‘CorrecTension’ system.
The effort didn’t stop there, they started using an improved design – using a steel body (which did allow them to use regular optical tubes) with decent mirrors and a much better overall setup.
In classic ‘everyone thought of it at the same time’ most telescope companies also started doing some upgrades to their Dobsonian line, but when Sky & Telescope did a review of six different new Dobs the Orion Skyquest, mostly due to its CorrecTension, was hands down the winner.
Nothing lasts forever and while Orion still is probably the #1 Dob seller, most other companies have found ways to match the SkyQuest’s capabilities, at least as far as balance goes. Tension knobs have replaced the springs on most models (including some Orion models) and it can be tricky to tell which Dobsonian models is the very best for your money but the fact is that you, as a regular telescope user, can now operate and use a Dobsonian without having to be a tube balancing genius.