Marine binoculars are designed to be used at sea, where magnification over 7x usually causes seasickness. These binoculars also offer great protection against the water and are not sensitive to high temperatures or their housing being exposed to sunlight.
Many of these binoculars also include a compass or some kind of reticle for range finding.
Porro prism design
A reticle for range estimations
At sea, having a compass is very useful for navigating and coordinating positions. To combine the compass and binoculars in one device seemed logical so that you do not have two things at once in your hands.
An analog scale on the bottom of the field of view of the compass with degrees written on (can be illuminated in more expensive models)
The digital display in the middle of the field of view (push the button to read the degrees, transparent display, which reduces transmittance. The compass is easier to use if it displays degrees in the middle).
Steiner Commander Global 7x50
Rangefinding Binoculars are more or less all very similar- having a scale in the middle of the field of view, with which you can calculate the distance to the observed objects if you know their size.
Good „miling“ requires a lot of experience and good prediction. It is the same principle as with tactical riflescopes. The scale is milliradian.
For now, there are no marine binoculars available with the laser rangefinder.
The 7x50 has established itself as a golden standard. While looking through the binoculars the 7x magnification does not shake the image to the point of getting seasickness, and our brains can normally compensate it.
Most of them have Porro prism because it makes them easier to seal and individual focus for each eye separately. 50 mm objective lens and 7x magnification give the 7 mm exit pupil, which is the most comfortable to use as it eliminates the trembling and allows us to always see a "full" picture.
Most modern marine binoculars have this function, as it is possible to use higher magnification for better details. Normally, such binoculars are larger, heavier, and more expensive.
They usually do not offer as good resolution as the classic ones with the same magnification. It is also a major weakness that they are not as reliable (less permeable if they fall into the sea and less resistant to falls) and bumps and are less bright.
They do, however, offer the use of higher magnification on moving boats due to their ability to stabilize the image.
This feature is extremely common in this type of binoculars, as it also achieves the best water tightness.
In Europe, Steiner has become an established provider of marine binocular to the extent that nobody else in the premium class actually produces them anymore (Zeiss, Leica, Swarovski ...).
Steiner Binoculars (Photo by Konrad Frost/Volvo Ocean Race. 23 October, 2017)
Configuration 7x50 and Porro prism are optimal because of a 7mm exit pupil, good light transmission, and focusing separated for each eye.
All these features mean that this type of binoculars is also the best choice for observing in the dark.
Due to all of the above configurations, they are perfect for dusk and dawn - however, they are not popular in hunting due to their special appearance, size, and inadequate colors.