Like all equipment, a good pair of marine binoculars is necessarily a compromise. The boat and the use we make of it will guide our choice.
The choice of a pair of binoculars to embark on your sailboat or motorboat requires you to immerse yourself a little in their technical sheet. Some features are important.
THE WEIGHT
It must be less than 1 kg. Even if you don't wear them for long, which is not the case in the mountains for example, binoculars that are too heavy tire the user's arms.
THE ENCOMBREMENT
If small marine binoculars store easily, it is difficult to stabilize vision. Their grip is less good.
THE TYPE OF PRISMS
The weight and size depend largely on the technology used to build the marine binoculars, including the type of prisms.
There are two prism systems:
- the prism on the roof (the light passes through the twin in a straight line)
- porro's prism (the offset of the prisms deflects the light beam)
Prisms of Porro
Roof Prisms
These prisms are both used to invert the image.
Roof prisms are lighter and more compact. Porro prisms have a higher optical quality than roof prisms. In the marine industry, since space is not an essential criterion, Porro prismatic binoculars are mainly used.
GLASS TREATMENT
For Porro prism binoculars, two types of lenses are commonly found:
- BK7
- BAK4
The main difference between the two lies in the density of the glass or the refractive index. BK7 uses borosilicate glass and BAK4 uses barium crown glass.
BAK4 is an excellent glass with a higher density that can eliminate internal light scattering and produce sharper images than BK7 glass. The BK7 loses some light that hits the edges of the prism.
There is a method to determine the treatment of lenses used with Porro prism binoculars. You hold the binoculars upside down away from your eyes in front of a light source to see the cone of light passing through. With the BK7 you will notice that there is a square shape cutting the part of the cone, while with the BAK4, you usually see the whole round cone.
MAGNIFICATION
A strong magnification is tempting to see further. Don't forget you're on a boat that's moving! It is then difficult to stabilize the image. At sea, x7 magnification is considered ideal.
BRIGHTNESS
This is a safety issue. In clear weather, at equal magnification, all marine binoculars are equal. But when it comes to discovering details of an anchorage or the entrance to a port between dog and wolf, a pair of binoculars that offers good brightness will perform better.
THE ADJUSTMENT CAPACITY
It's nice to grab your binoculars and see quickly. Some binoculars have a central adjustment knob, others are net from 20 m to infinity without adjustment. It's all about taste and usage.
Wearers of corrective eyeglasses appreciate the adjustable marine binoculars because they can remove their glasses and get their optical correction through the binoculars.
WATER RESISTANCE
I know, you're not gonna use your binoculars underwater! Why take a pair of waterproof marine binoculars? Simply so that moisture, and even dust, does not enter the binoculars.
EYEGLASS WEARERS
The wearers of glasses will have to fold down the windscreens to use the binoculars (on our photo, the windscreen on the left is folded down). Unless you remove the glasses and correct the binoculars at his sight. The interpupillary distance can be adjusted by moving the binocular bodies closer together or apart.
THE INTEGRATED COMPASS
Some models have an integrated compass. A rose appears in an optic indicating the aiming direction. A reticle is present to evaluate the distances. Often this compass has a light (usually red so as not to dazzle). These marine binoculars with compass lighting poise a battery compartment that powers the lighting.
