Eye cup – these usually pop, twist or fold up and down. Always use it extended unless wearing spectacles.
Eye piece – these are often sold separately to the main body of the telescope. Usually expressed as the width viewed in metres from a set distance, such as 1000 metres or in degrees. (eg. 1° = 17.5m approx.) The exception is the wide angle eyepiece.
Field of view – is directly related to magnification. The greater the magnification the smaller the field of view. The eyepiece controls the field of view not the objective lens.
Focus control - allows you to focus on any subject at any distance.
Magnification – 20x, 40x and 60x are the most popular for bird watching. Anything smaller does not really get you close enough and higher magnification is difficult to hold steady.
Numbers – these tell you the magnification and the objective diameter eg. 20x60 means 20 times magnification and a 60mm objective diameter. A telescope with a zoom eyepiece may be expressed as 20-60x60, where the 20-60x is the range of the zoom from 20 times to 60 time magnification.
Objective lens – the big ones nearest whatever you are watching. The bigger the better for light gathering and a generally brighter image.
Resolution – on a bright day, a good telescope should be able to resolve two black dots 1.5mm apart on a white surface at a distance of 50m.
Rubber armour – a scuff and knock resistant covering. |
