National Geographic 10x42mm Waterproof Binocular, Black
Two figures on this specification sheet describe low light performance directly, and almost nobody knows how to read them. Light intensity is listed as 17.64 and twilight factor as 20.49. The first describes how much light the pair delivers to your eye. The second is the number that predicts how much detail you will actually resolve at dusk, when most animals move.
What the 10x42mm figures translate to
A higher twilight factor means more usable detail in poor light, which is why 42 millimetre objectives paired with 10x magnification remains a standard choice for early morning and late afternoon observation. The field of view is 101 metres at 1000 metres, or 5.77 degrees, which is the trade you accept for the extra reach that 10x provides over the more common 8x.
Focusing, mounting and storage
Focus runs through a central wheel with a separate diopter setting so each eye can be corrected independently. Twist up eye cups suit eyeglass wearers, and a tripod adapter thread is fitted for long sessions where holding 710 grams steady stops being realistic. The body is BaK-4 prism glass with multi coated optics in a rubber and plastic armoured housing, supplied with dust caps for both eyepieces and objectives and a case for carrying.
Full features and the complete specification table appear below.
Features
- 10-fold magnification
- Solid, waterproof body
- High contrast and true colour image
- Safely stored and easy to carry in included case
- Suitable for eyeglass wearers
Specifications
| Optical Design |
Roof |
| Magnification |
10x |
| Mirror/Lens Diameter |
42 mm |
| Material Prismn |
BaK-4 |
| Type Of Coating |
Multi coated |
| Eyepieces For Eyeglass Wearers |
Yes |
| Diopter Setting |
Yes |
| Field Of View At 1000m |
101 m |
| Field Of View |
5.77 degrees |
| Light Intensity |
17.64 |
| Twilight Factor |
20.49 |
| Colour |
Black |
| Waterproof |
Yes |
| Colour |
Black |
| Body Material |
Plastic |
| Tripod Adapter Thread |
Yes |
| Focusing System |
Central focus wheel |
| Eye Cups |
TwistUp eye cups |
| Interpupilar Distance Min |
73.72 mm |
| Interpupilar Distance Max |
73.72 mm |
| Body Armouring |
Rubber/Plastic |
| Dust Protection Caps |
Dust caps for eyepiece and objective |
| Net Weight (Without Access.) |
710 g |