More about magnification

All about magnification

Remember magnification is limited by several factors, all telescopes are limited to a theoretical maximum of 50x per inch under optimum conditions. This means that a 60mm telescope can use a maximum of around 120x under perfect conditions. Even the very largest instruments are limited to around 250x magnification under UK skies as the turbulent atmosphere simply will not allow more. So next time you see advertised magnifications of several hundred quoted they are not practical in the real world! Remember to see Saturns rings you only need around 50x and deep sky objects such as Galaxies and Nebula often require even lower powers. Even modest Binoculars at 10x magnification will show Jupiters four moons strung out from the planet.

It is far better to have a clear bright view of an object at the correct magnification than a dim blurred image with too much magnification.

Light Gathering Power
The prime function of a telescope is to gather light. The larger the telescope, the more light it can gather. Telescopes are rated by their aperture so a 152mm (6") instrument has a lens or mirror which is 152mm in diameter has four times the light grasp of a 75mm (3") instrument.

Magnification - How Big
Simply changing the eyepiece will vary the magnification that a telescope provides. Magnification is equal to the telescope’s focal length divided by the eyepiece’s focal length. For example a 10mm eyepiece on a telescope with a 1000mm focal length would provide 100x magnification.

Resolution - How Much
Resolution is a telescope’s ability to reveal fine detail; especially low-contrast detail such as the ability to split binary stars and reveal details on the Solar System’s objects. A 100m (4") telescope will resolve detail under perfect conditions to 1.1 arc second where a 200mm (8") will reach around 0.58 of an arc second, double the resolving power.

Eyepieces are available in two formats, 1.25" (standard on most telescopes) and the larger 2" size that offers wider fields of view for telescopes equipped with 2" focusers. The design and number of elements in eyepieces dictate how wide the field of view that you see is. There are three types of design generally available, Plossl (approx 50 degrees) Super Wide (approx 68 degrees) and Ultra Wide (approx 82 degrees). Most modern eyepieces are equipped with filter threads allowing the use of colour or light pollution filters to enhance views.

If you wear spectacles long eye relief eyepieces are recommended but you should only need to wear them if your prescription is for astigmatism, long and short sight issues can be easily resolved with a slight refocussing of the instrument.