People were asking me about Fairlie nomenclature on the Train Misconductor Discord so...
The first builder of a Double Fairlie locomotive was a wealthy astronomer and optician making and selling telescopes and binoculars--locomotive design started off as a sidegig. The first single Fairlies were called Telescope types having "Shaflaauh Telescope & Optics Company" on the builder's plate; therefore the Double Fairlies became known as Binoculars. Since the Doubles were a lot more popular than the Singles, the Singles eventually became known as Monoculars instead when built by other builders.
The planet Flibul was actually discovered using a Shaflaauian telescope, which is a particular kind of corrected doublet telescope intended for focal viewing (as opposed to afocal viewing with an eyepiece)
In a normal visual telescope the entire system doesn't actually have a focal length, only a magnification factor. The telescope itself has a focal length, and the eyepiece has a focal length, and if you divide one into the other you get the magnification. So my 6" f/8 Dobsonian reflector with a 1200mm focal length using a 25mm eyepiece has a 48x magnification. This afocal imaging requires that the imaging device have its own lens for focusing light. This could be the lens of a smartphone camera or the lens in your eyeball.
But when doing serious astrophotography, the telescope is used without an eyepiece with a camera that is used without a lens. As a result you have the telescope essentially acting as a powerful photographic telephoto lens. This is a focal imaging setup. The light comes to focus on the imaging sensor.
On Gymnome, though, the astronomers can do occular shapeshifting. While traditionally this practice has been to shapeshift one's eye lens to form bigger and bigger telescopes, this tops out at only about an inch or two of aperture, beyond which abberations due to the sloppy gooey structure of the eye lens make it impossible to see more detail. When glass and metal telescopes were invented, they were used to replace the eye lens, so the occular shapeshifter would shapeshift their eye lens flat, blinding themselves without the help of an artificial lens or mirror to focus light--the telescope's objective.
Eventually occular shapeshifters started going permanently blind in one eye and needing contact lenses at all times to see, leading to the development of the telescope eyepiece lens. But some visual astronomers still swear by focal viewing.
Sketch of Eaurp Guz, a Gymnomi Slime, on Earth, using an ancient 21st century telescope set up for afocal viewing, as all visual work telescopes on Earth do.
The distant ice giant planet Flibul, as if seen using afocal viewing in a powerful telescope.
