What comes with the tube
Each refractor here ships with a 2-inch diagonal, its focuser, a dovetail and a finder base. The dovetail sits on cradle rings with a carry handle, except on the two ED80s, which have it built into the tube. The AR doublets add an 8x50 straight-through finder. None includes an eyepiece, so budget for at least one, and for a finder on the ED and FCD100 triplets. The FirstLight 127 Maksutov comes with a 25 mm eyepiece, a 1.25-inch diagonal, a red-dot finder and a smartphone adapter.
Matching a mount
Dovetail
The refractors attach by dovetail: Vixen-style on the AR doublets, the ED80s, the ED102s and the FCD100 127s, and Losmandy-style on the ED152. Check that your mount's saddle takes that style before you buy.
Payload
Add up the tube and everything you will hang on it, and stay inside the mount's rating, which runs lower for imaging than for visual use. The tubes weigh from 5.95 lb for the ED80 to 23 lb for the AR152. Explore Scientific's iEXOS-100 carries about 9 lb of equipment, and its EXOS2-GT 28 lb of instruments for imaging and 40 lb for visual use.
Refractor or Maksutov
An AR doublet gives more aperture for the money than a triplet and suits visual observing, though it shows a violet fringe on bright targets. The ED and FCD100 triplets correct that color, which makes them the tubes for astrophotography. The FirstLight 127 Maksutov folds 1,900 mm of focal length into a short tube at f/15, for high power on the Moon and planets.
Frequently Asked Questions
What does OTA stand for?
Optical tube assembly: the telescope itself, meaning the tube with its lens or mirrors and its focuser, without a mount or tripod.
Can I do astrophotography with an OTA?
Yes, on a tracking equatorial mount. Image with the ED and FCD100 triplets: the color fringing an AR doublet shows at the eyepiece becomes a real problem in stacked images.
Why buy a tube alone?
To use a mount you already own, or to choose one for the job, such as a tracking equatorial mount for imaging. A second tube with a different focal length also gives you a different field of view on the same mount.
For mounts to carry these tubes, browse our equatorial mounts and GoTo mounts, and for the glass behind the triplets, read APO vs Achromatic Refractors.