National Geographic 20-60x60 Spotting Scope: a twilight factor of 34.64, and what that number is telling you
Spotting scopes are sold on magnification and bought for what they show at dawn and dusk, which are not the same thing. This National Geographic scope zooms 20x to 60x through a 60 millimetre objective, and the number worth understanding is the twilight factor of 34.64.
Twilight factor and light intensity
Twilight factor combines magnification and objective diameter to estimate how much detail a scope resolves in poor light. Higher is better. At 34.64 this stays genuinely useful through the first and last hour of daylight, which for game viewing and birding is most of the time you would want one.
The light intensity figure of 9 derives from the exit pupil and describes how much reaches your eye. Both say the same thing: the 60 millimetre objective gathers enough that high magnification will not leave you a dim image.
National Geographic 20-60x60 magnification and field of view
At 20x the field of view is 29 metres at 1000 metres, or 1.66 degrees, wide enough to find something and follow it. Winding to 60x narrows that in exchange for detail, which is how a zoom scope is meant to be used: locate wide, then close in. Near focus is 12 metres, so it works on something nearby as well as at distance.
Build and what is included
The body is metal with rubber and metal armouring, weighing 998 grams at 350 by 155 by 95 millimetres. Optics are fully coated, and removable dust caps protect both ends. A table tripod is supplied, which at 60x is not optional: hand holding at that magnification gives an unusable image however good the glass.
Features
- Compact and lightweight spotting scope for travelling and hiking
- Large objective lens diameter for a high light gathering capacity
- Table tripod included for added stability
- Magnification range: 20x-60x
- Objective lens diameter: 60mm
- Field of view: 29m@1000m (20x)
- Dimensions: 350x155x95mm
Specifications
- Magnification Zoom min.: 20
- Magnification Zoom max.: 60
- Type of coating: Fully coated
- Colour of coating: blue
- Field of view at 1000m: 29 m
- Field of view: 1.66 degrees
- Light intensity: 9
- Twilight factor: 34.64
- Near focus from: 12 m
- Body material: Metal
- Body armouring: Rubber/Metal
- Dust protection caps: for objective and eyepiece, individually removable
- Net weight (without access.): 998 g
What's in the Box
- 1 x NATIONAL GEOGRAPHIC 20-60X60 SPOTTING SCOPE