Eyepiece Selection For Your Telescope

 “I am confused – which eyepiece should I use for what object ??”  It’s actually very easy, all you need to do is follow the following steps:

  1. 1.      Telescope

It doesn’t matter what type of telescope you have, the calculation is the same


Two of our best sellers – Saxon 909Eq2 & Saxon Dob 6

  1. 1.      Focal Length of your telescope

You need to find out is what is the “Focal Length” of your telescope. This is found on the side of the telescope, a sticker will show – as example:

D = 90mm F = 910mm

The number you are interested in is – F = 910mm

The 90mm example means the size of the lens (in the case of a reflecting telescope the primary mirror)

  1. 2.      Eyepieces

Then get out your eyepieces and take a look on the side of the barrel, it will show the size

Typical 25mm & 10mm eyepieces

  1. 3.      Calculation of magnification

You simply divide the size of the eyepiece into the Focal Length of the telescope


Magnification # 1 = F 910mm divided by the 1st eyepiece which is a 25mm = 910/ 25 = 36 Magnifications

Magnification # 2 = F 910mm divided by the 2nd eyepiece which is a 10mm = 910/ 10 = 91 Magnifications

Simple as that J

  1. 4.      Eyepiece selection

Which eyepiece do I use for what object ??

Your telescope will usually be supplied with two eyepieces

A 25mm & 10mm –  This is not sufficient to maximise your viewing experience – you need 3 eyepieces to maximise your viewing capability

Low power – General viewing 25mm

Medium power – Higher magnification 10mm

High Power eyepiece – you will not have one of these supplied with the telescope – recommendation – 6.5mm Premium Plossl – our biggest seller –

See Here For our eyepiece range



Everwin 6.5mm Premium Plossl – Quality is a MUST for high power viewing

(Highly recommended)

  1. 5.      Which eyepiece to view what object

25mm – Low Power – viewing stars, star clusters, nebulae & deep space

10mm – Medium Power – the Moon & distant deep space objects – achieving a close up

6.5mm – High Power – the Moon & Planets – this is a must to see detail in the planets, such as Saturn’s rings, Jupiter’s cloud bands & Great Red Spot, and high detail on the Moon. It’s as  simple as that

Questions ? – Astronomy Alive are Australia’s leading specialists in astronomy gear, call Cris to discuss your eyepiece selection or other astronomy needs


03 9576 5325 – 0412 318 125

C – Astronomy Alive – 24th Oct 2012









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