Aperture – defines the size of the telescope opening, larger apertures allow more light into the telescope and is one of the most critical choices when choosing a telescope. Larger apertures are more complex and expensive, as well as make the telescope less portable.
Astrophotography – using a camera with a telescope.
Eyepiece – also known as an ocular, where you view the light collected by the telescope.
Finderscope – low powered telescope mounted coaxially to the main telescope with a shorter focal length, allowing for more sky to be seen at one time for getting an initial track on the object you want to observe with the main telescope.
Focal length – the focal length determines how much, or little, of the sky, can be seen at any given time. The longer the focal length, the narrower the field of view, and the higher the magnification.
Focal ratio – an expression of the focal length by the aperture. Typically between f/5 and f/15.
GoTo – the capability to place the telescope under computer control to find an object.
GPS – an optional part of a goto system to help find alignment stars, while helpful, it is not critical to using a goto system.
Lens coating – lens treatments to reduce reflection, increase transmission, improve the limiting magnitude
Limiting magnitude – lighting conditions (including ambient light) that affect how faint objects can be seen.
Magnification – the focal length of the main lens by the focal length of the eyepiece.
Types of Telescopes:
Refractor – the stereotypical telescope, easy to use, rugged and assessable to most people.
Reflector – invested by Newton, a more compact design and cheaper than refactor designs.
Catadioptrics – the most portal design, though it is more expensive and the mirrors and optics produce a blind spot on the center of the image.
That about sums it up for the basic telescope terminology! If you are comfortable with these terms, you’ll be able to speak to any astronomer confidently, and without embarrassing yourself…=)