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Orion 2" Rack and Pinion Focuser
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In the interest of full disclosure, I have no financial stake in any of the companies mentioned in the following article.
When it comes to finding components for amateur telescope making, some areas of the market are burdened with an embarrassment of riches while others are anemic when it comes to options available to the consumer. When it comes to small mirror cells or tubes, most ATMs are limited to a small number of suppliers. When it comes to focusers, however, there are dozens upon dozens of choices available to the amateur astronomer. Recently it was necessary to replace the (broken) stock plastic 1.25” focuser on my late model Orion “Deep Space Explorer” Dobsonian. Since budget was a serious issue to consider, I looked to the low end of focusers on the market. I settled on the cheapest available focuser that still had the appropriate racked-in to fully-extended height range without having to reposition the secondary mirror. I also wanted to change from a 1.25” focuser to a 2” unit, so I went for the Orion 2” cast-aluminum rack and pinion focuser manufactured by Synta.
When the focuser was received, it was oozing excessive quantities of “alien snot,” also known as “Synta Glue,” “Gluebricant” and “Jeez, what the heck IS this stuff?” I don’t think I will ever understand why so many Chinese companies lubricate their components with this sticky grease. It actually detracts from the functioning of the instrument, and it has terrible thermal properties (stiffening when the temperature drops). The first order of business was to degrease and relubricate the focuser. The unit had to be completely disassembled and each component cleaned in a two step process. First, liberal quantities of WD-40 were used to break down the glue. Second, 409 degreasing cleanser was used to clear away the WD-40/Glue mixture. This may have to be repeated to fully eliminate all traces of the glue, and a toothbrush makes a great tool for scrubbing in the notches between gear teeth in the R&P mechanism. Afterward, apply moderate amounts of white lithium grease to the R&P mechanism components and reassemble the focuser.
After reassembling the focuser and installing it on my telescope, it moved reasonably smoothly and the lock knob provided good tension control. The lock knob is good and large, so I’m even able to adjust it with gloves on. Focusing accurately at high magnification is difficult, however, unless the tension knob is completely loosened. There are also occasionally minor “jumps” and “jerks” in the travel. Compared to the plastic unit my scope was originally supplied with, however, it functions beautifully. High-end Crayford units will still put it to shame.
The focuser has a relatively low profile for a rack and pinion unit. This does, unfortunately leads to the focus knobs sitting barely above the focuser’s base, and fingers can be pinched between the two. As for the plastic knobs themselves (made of a particularly brittle variety of plastic), the knurled grip around the edges is uncomfortable to grip. I’ve heard them being referred to as “plastic teeth out for blood.” In the aforementioned situation of fingers getting pinched between the focuser base and the knob, these plastic teeth can inflict some painful damage. I took to wrapping strips of electrical tape around the knobs to lessen their painful nip. Luckily, multiple companies sell replacement focus knobs for Synta units. I eventually intend to replace the knobs with rubber-grip knobs, and hopefully ones of a slightly smaller diameter.
Apart from the brittleness of the focus knobs themselves, the overall build quality is reasonably high. The all-metal construction is a welcome relief to the all-plastic focuser I was using previously. The included 2” to 1.25” adapter is made of solid, anodized aluminum and fits tightly into the focuser. 1.25” eyepieces correspondingly fit tightly into the adapter. I don’t foresee any centering issues with eyepieces or collimation tools.
This focuser is certainly not perfect. It has several issues that cause it to come up lacking compared to better focusers, even ones within Orion’s product line. Ultimately, you get what you pay for. However, for only 7 dollars more than the cheaper plastic focuser it was replacing, it does provide a decent, reasonable option for ATMs on a budget, or owners of cheap plastic focusers looking for a modest upgrade.