How to: Finding Telescope Magnification

Finding Telescope Magnification
What’s the Magnification of Your Telescope?

Finding your telescope’s magnification is an important part of a purchase process. However, working out the magnification of your telescope or working out the magnifications when choosing a telescope to buy can seem difficult and confusing. Most people generally look for higher magnifications when looking for a telescope but have no idea how to find the magnification. Don’t worry guys, you’re not the only one. In fact, working out the magnification isn’t that hard at all. Most of them are easy to obtain with the information given on the specifications list. Just add a little maths! This process also enables you to get to know your telescope more.

Factors you need to know:

  • Focal length(mm) or focal ratio
  • Size of eyepiece (mm)


Magnification = Focal length (mm)/size of the eyepiece(mm)

If the Focal length was not provided and you only know the focal ratio

Focal length=F-ratio x aperture of your telescope

Example 1:

Saxon 1309EQ2 Reflector Telescope w/Steel Tripod


Saxon 1309EQ2 Reflector TelescopeSpecification for Saxon 1309EQ2

From the above specifications, we gather that the focal length the Saxon 1309EQ2 is 900mm.

Three eyepieces are supplied with this telescope, the 4mm, 10mm and 25mm.

When a 25mm eyepiece is used:

Magnification =900/25= 36x


When a 10mm eyepiece is used.

Magnification= 900/10= 90x


When a 4mm eyepiece is used.



Example 2:

Celestron Nexstar 8 SE Computerised Cassegrain Telescope

Celestron Nexstar 8 SE Computerised Cassegrain Telescope

We can see from the specifications list the focal length of this telescope is 2032mm

Magnification = Focal length(mm) / Eyepiece size (mm)

With a 25mm eyepiece used:


**Other eyepieces can be used to reach much higher magnification**


Example 3:

Saxon Hyperion 1021EQ3 Refractor Telescope

Saxon Hyperion 1021EQ3 Refractor TelescopeSaxon Hyperion 1021EQ3 Refractor Telescope

We can see from the specifications list the focal length of this telescope is 1000mm

Magnification = Focal length(mm) / Eyepiece size (mm)

25mm Eyepiece Used:

Magnification=1000/25= 40x


10mm Eyepiece Used:

Magnification= 1000/10=100x


Is higher the magnification the better?

**As shown in the above examples, finding telescope magnification is not difficult after all. However, please keep in mind that a telescope’s magnification is not everything. Is higher the magnification the better? The answer would be it depends, the ideal type of telescope for you depends on your needs and what you want to see.**

For lunar and planetary observation, the refractor would be the ideal choice as the refractor is made of lenses and is able to provide images with higher clarity when viewing to moon and the other planets.

Product examples:

Celestron AstroMaster 70EQ Saxon ED100 EQ5 GOTO Refractor Telescope Saxon Novo 909 AZ3 Refractor Telescope
Celestron AstroMaster70EQ Saxon ED100 Refractor Telescope
For fainter stars and deep-sky objects like the nebula and galaxies, reflectors are the ideal choice since they’re relatively inexpensive to reach the aperture needed to view those objects.

Product examples:

Saxon 15075EQ3 Reflector Telescope w/Steel Tripod Skywathcher 10” GoTo Computerised Dobsonian Telescope Saxon 8” Dobsonian Telescope
Saxon 15075EQ3 with Steel Tripod Saxon 8" Dobsoinan Telescope
For much fainter stars and deeper space objects the cassegrain telescopes are the ones to go for since they have more efficient light gathering power as oppose to the reflectors, the cassegrain telescopes are more compact, requires a smaller aperture for the same result a reflector would deliver.

Product examples:

Celestron Nexstar 6SE Computerised Cassegrain Telescope Celestron CGEM 1000HD Computerised Telescope Celestron CPC 925 Computerised Cassegrain Telescope.
Celestron CGEM HD 1100 Celestron CPC800


Highest Practical Magnification

However, we also need to be mindful of the Highest Practical Magnification. Typically, on an average viewing night, the highest practical viewing power for each inch of aperture of your telescope is around 25x-30x magnifications. This means for a 3 inch (76mm) aperture telescope, the highest practical magnification on an average night is 90x magnification etc.

In conclusion, taking care of the magnification of your telescope is easy, we just need to take into consideration of your needs and the highest practical magnification. At last, go out there and enjoy astronomy!




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