How to calculate magnification (power) of a telescope or spotting scope?

1. Identify the focal length of the scope. This is often marked on the body of the scope or it should be given in the user manual. For example, the Nipon 26-78x78 scope's focal length is 780mm.

2. Find the focal length of the eyepiece. For example, for the PL16, PL26 and PL32 eyepieces as listed in eBay Shop Nipon Scopes & Binoculars, their focal length is 16mm, 26mm and 32mm, respectively.

3. Divide the focal length of the scope by the focal length of the eyepiece to get the magnification of the scope. For example, if you wish to use a 16mm eyepiece to replace the 26-78x zoom eyepiece of the above Nipon scope, the magnification of the scope will become: 780/16=48.75 (or approximately 49x).  

It is desirable to have a range of eyepieces with different focal lengths to allow viewing over a range of magnification levels.

Please keep in mind that, as a fundamental law of optics, at higher magnification powers an image will always become dimmer and less sharp.  With every doubling of magnification you lose about half the image brightness and 3/4 of the image sharpness.

Therefore, it is best to begin viewing with the lowest power eyepiece (with longest focal length, eg. 32mm of the above example) or with the zoom eyepiece being adjusted to its lowest power level. This will provide the widest true field of view which will make target finding and centring much easier. After you have located an object, you can switch to a higher power eyepiece (with smaller focal length) to see more detail (if atmospheric conditions permit). If the image you see is not crisp and steady, reduce the magnification by switching to a longer focal length eyepiece, or for a zoom eyepiece, zoom out. In general, a small but well-resolved image will show more detail and provide a more enjoyable view than a dim and fuzzy, over-magnified image.

Please refer to "How to calculate the field of view" for more related information.

What is the maximum magnification power a telescope or spotting scope can achieve?

As described above, the higher the magnification level, the dimmer an image becomes. There is thus a golden rule for the maximum usable magnification (Mmax) of any scope:

Mmax=2 x D (mm)

Where: D is objective lens diameter measured in mm.

For example, for the Nipon 26-78x78 compact zoom scope, its objective lens is 78mm, so the maximum usable magnification power of this scope is 2x78=156 times.

How to decide the smallest eyepiece a scope can use?

Based on the Mmax value as calculated above, you can decide the minimum eyepiece focal length that you may wish to use for a scope. The equation is: f = F / Mmax

Where: f is the minimum eyepiece focal length (mm); F is the focal length of the scope; Mmax is the maximum usable magnification of the scope.

For the Nipon 26-78x78 scope, the minimum eyepiece which can be used is: f=780/156=5 mm. This would provide about 156x power which is nice for viewing Mars or resolving the rings of Saturn. To resolve Saturn's rings, you may only need about 30x power, but to see them more clearly, higher magnifications are required.

How much magnification do I really need to get a good image?

If the visual condition is good (eg. on nights when the sky is clear and stable), the top usable magnification for a 60mm (2.4 inch objective lens) scope will be around 2x60=120x. This is more than enough to see the rings of Saturn, cloud belts on Jupiter and many star clusters and nebulae. So, 60mm scopes have been the standard size for a wide range of applications. Two types of these models are available at Nipon Scopes & Binoculars, one is Nipon 15-46x60 Spotting Scope, the other is Nipon 700x60 Telescope. 

With a 70-80mm scope, however, the amount of light it gathers is about 55-65% more than a 60mm scope. This improves image quality especially when viewing at high powers and under low light. The choices of these models are Nipon 20-60x70 Spotting Scope, and Nipon 26-78x78 Compact Zoom Spotting Scope/Telescope. In general, larger scopes outperform smaller ones, but they also tend to be bigger and heavier, and more expensive.

How to calculate the field of view of your scope?

1. Find out the value of the apparent field of view of the eyepiece. Every eyepiece has its own value of the apparent field of view and this value is supplied from the manufacturer. For the optical eyepieces PL16, PL26 & PL32 as mentioned in the above example, their apparent field of view is 52 degrees.

2. Find the value of magnification. This is calculated by dividing the focal length of your scope by the focal length of the eyepiece. For the Nipon 26-78x78 scope (focal length=780mm) with a 16mm eyepiece, for example, its magnification will be:  780/16=48.75.

3. Divide the value of the apparent field of view by the value of magnification. For the above example, 52/48.75=1.06 degrees. This is the value of the field of view for this scope using this eyepiece.

What's the difference between angled and straight eyepieces?

Some scopes come in either straight or 45 degree angled eyepiece designs. Straight scopes used to be the norm of these products, but angled scopes seem to have taken over for a majority of users nowadays.

With a straight design, you can view the target in line with the central line of the scope. Some people find it a lot easier to locate a target in this way, especially when the target or the viewer is moving. The straight eyepiece is also useful when you use the scope in a confined environment such as a car or from a seated position (such as wheelchair user).

Angled scopes can better accommodate people of different heights, and they seem to be easier to use for digi-scoping (eg. to mount a digital camera). Nevertheless,  either option is strictly a personal choice, and both options are available from this shop.

Should I go for zoom or fixed power scopes?

Most scopes are available with zoom or fixed power eyepieces which can range from 15x to 60x. Zoom eyepieces have become popular in recent years especially for many birders. It's easier to find your object at low power (with a wider field of view) and then zoom in to see more details. This gives you much convenience and saves you trouble changing eyepieces for different magnifications. However, it should be noted that even though zooms are optically very sharp, they have a relatively narrower field of view as compared with fixed power eyepieces at the same magnification level. Looking through a good scope with a fixed wide angle eyepiece (eg. 32mm) is a joy! If you put two scopes together, one with a 20-60 zoom set at 30x power, the other with a 30x fixed power eyepiece, the difference is striking. You can actually get a wider field of view in the 30x than you will with the zoom even at 20x. That's why we have made a set of fixed power eyepieces available as optional accessories in Nipon Scopes & Binoculars shop, with 16mm, 26mm and 32mm focal lengths. They can add greater values to your scope.

Can I attach a digital camera to the scope?

There is an increasing requirement for attaching digital camera to a scope to take pictures of distant objects. You can achieve this by hand holding the camera, for example, or by mounting the camera on a tripod next to the telescope eyepiece, building or buying an adapter to hold the camera over the eyepiece, using a universal camera adapter to attach to the camera lens, or using an eyepiece with built in adapter to attach it directly to the digital camera. Or simply, you can use a digital eyepiece which takes pictures and video footage directly through the scope.

The Nipon 26-78x78 compact scope can be fitted with an eyepiece adapter which has a 1.25" (31.75mm) slip socket as an eyepiece holder. The adapter is CNC precision-machined from aluminium and has a black anodised finish. With this adapter, you can fit a digital eyepiece/camera (please see a separate technical note on "Digital eyepiece for Nipon telescopes/spotting scopes"), or fixed power optical eyepieces to this scope.  This adapter also allows a standard-design T-mount SLR and CCD camera adapter (with 1.25" fitting) to fit into its eyepiece holder.

A standard T2 mounting ring will need to be purchased separately for your particular camera brand from the camera's manufacturer. Please contact us for useful links with more information about the camera adapters, as the present site can only contain links to eBay pages. 

Please visit Nipon Scopes & Binoculars or nipon-scope.com for a range of scopes and accessories.

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Thank you!