It can be challenging to explain the attributes of a telescope to a novice. I will now cover the basic terminology of telescopes.
This is the size of the opening in a telescope where the mirror or lens collects light. This factor is important because telescopes function off light gathering. More photons are collected when the aperture is larger. The size of the aperture calls for a higher price and a larger telescope. Aperture is measured in millimeters or inches (25.4 mm is equal to 1 inch).
The focal length is the distance from the objective lens to the point where the light comes into focus. The longer the focal length, the larger the image if at the point of the focal plane, and the higher the magnification is for viewing the sky at night. Local focal lengths are ideal for small objects like double stars, planets, and etc. Focal length can also be measured in millimeters or inches.
To get the real focal ratio, you must take the focal length and divide it by the aperture. A fast focal ratio is normally considered to be f/4 or less. Mid-range focal ratios range from f/5 to ff/8, and slow ratios start at f/9. A fast focal ratio will help the telescope record the image faster.
Taking its name from Peter Barlow, this lens increases the effective focal length.