1. Properties of Telescopes

2. Magnification Magnification is how much larger an image in a telescope is when compared to when the object is seen by the naked eye. Magnification is measured in multipliers 20x means that the image is twenty times as big This is called the magnification power of the telescope

3. Finding a Telescope’s power The focus of a mirror or lens is where it makes parallel rays of light meet. Focal length is the distance from the lens/mirror to the Focus To find the power of a telescope just: Divide the objective’s focal length by that of the eyepiece. Power = f o /f e It is possible to change power of a telescope by changing the eyepiece

4. Aperture The Aperture of a telescope is the diameter of its objective. Aperture determines two things The brightness of the image…the larger the aperture the brighter the image will be Particularly important for very dim objects like nebulae and galaxies Resolution

5. The Resolution of a telescope is how well it can show details The aperture is the main factor determining the resolution …the greater the aperture the better the resolution. Resolution is also affected by the quality of the lenses and mirrors. Badly made ones have distorted or fuzzy images known as aberrations.

6. Magnification is useless if the image is dim or the resolution is bad (all you get is a big dim and blurry image!) Therefore the most important property of a telescope is its… Aperture!