Pic by Zane Landers
The Explore Scientific Twilight I mount is an alt-azimuth mount that pivots left to right and up/down on ball bearings.
Unlike cheap alt-azimuth mounts based on the design of a fluid head tripod, where the telescope is suspended above the axis of rotation, the Twilight I puts your telescope’s optical tube sideways of the altitude axis. This avoids the common problem of the telescope tipping when aimed high in the sky, which happens with photo tripods and mounts like them due to their inherently unbalanced nature. When you balance your telescope properly on the Twilight I, it remains so regardless of where it is aimed in the sky. There are clutch levers on both the altitude and azimuth axes just in case, however.
While it has a stated weight capacity of 8.16 kg, the Twilight I works best with telescopes under 6.8 kg, including all accessories—so a 6” SCT or Maksutov, a 6” reflector, or a 4-5” refractor is probably the upper limit.
The arm holding the altitude axis for the Twilight I can be adjusted in angle to ensure the back end of your telescope adequately clears the mount’s base; a hex key to adjust the mount is provided and fits neatly in a cover on the azimuth axis.
The Twilight I features standard slow-motion cables to make fine tracking and pointing adjustments on either axis, which is particularly useful at high magnifications. Due to manufacturing tolerances, there can be some backlash/slop in the gears that these cables connect to for adjustment. However, in most cases, this is not a huge concern.
To attach to your telescope, the Twilight I has a standard Vixen-style dovetail saddle that will clamp to any scope with a dovetail bar. The saddle uses a set screw with an additional safety screw to firmly grasp your scope’s dovetail plate.
The key to the Twilight I’s stability is its 1.75” steel tripod. This tripod is heavy, but it’s rock solid, and the bottleneck limiting this mount’s weight capacity is solely the mount head. A near-identical tripod is provided with the Sky-Watcher HEQ5, which holds more than twice as much weight as the Twilight I is meant for.
An accessory tray/spreader bar insert provides additional bracing for the legs and has slots for three 1.25” eyepieces—though in most cases you’ll probably not find yourself using it for this purpose.
Should I buy a used Explore Scientific Twilight I?
A used Twilight I has relatively little that can actually go wrong with it, being a manual mount. However, you should, of course, inspect the mount for any obvious corrosion or damage.