Almost anyone who has a love of the outdoors will own at least one pair of binoculars in their lives.
Depending on your interests, whether they be following sport or horseracing, golf, yachting and other marine recreation, motor racing, birdwatching, hunting – you name it – you may need more than one set of binoculars to cater for your specific needs.
Like a lot of things in life, what you get out of it is in proportion to what you put into it. This goes for binoculars as well!
What follows is a discussion of the features that you need to weigh up when making the decision to invest in a pair of binoculars. It’s worth reading through this technical review as a good set of binoculars can easily last a lifetime.
HOW BINOCULARS ARE SPECIFIED
There are many numbers that describe a pair of binoculars but the first and foremost is a set of 2 numbers. This is as fundamental as specifying diesel or petrol engines, sail or power, etc.
A typical number set would be, say, 7 x 50 or 8 x 32.
The first number identifies the magnification power. Magnification power indicates how much closer an object appears to you when looking through the binoculars. The laws of physics cannot be sidestepped, however, and the greater the magnification, the lesser the brightness. As you can imagine, the bigger the magnification, the smaller the area of the image you are looking at. This smaller area has proportionally less light than a less magnified larger area. To compensate for this, you have to make the opening into the binoculars as large as is reasonably possible.
With, say a 7 x 50 binocular you have 7 x magnification but 1/7th the brightness all other things being equal. A 50mm lens (objective lens) is a good compromise to receive a reasonable amount of light. You hardly see larger than 50mm (the objective lens) in a hand-held binocular.
MORE TO KNOW. MAGNIFICATION VS. BRIGHTNESS
If you just want a set of binoculars for a boat, select a 7 x 50 if your boat is under 50 feet. The 7 x 50 is a great compromise between good magnification (7 times) and a wobbly image. The more the mag, the wobblier it gets.
The brightness of the image in the eye piece is mainly a function of the magnification. Beware!! Maths to follow!!
SO, UNLESS YOU WANT TO PUT A PAIR OF HIGH-MAG BINOCULARS IN YOUR POCKET, GO FOR THE BIG OBJECTIVE LENSES.
OTHER BRIGHTNESS FACTORS
Apart from the relative brightness issues you can lose brightness in other ways. If you are suckered into buying cheap binoculars up to 50% of the light entering the objective lenses will disappear. This is because the glass optics and the coatings on the optics are cheap.
Our best binoculars will allow from 93-95% through. Even our fairly cheap units will allow at least 75% through. When we don’t mention a number in our selection guide under “Light Transmission efficiency” it means around 50%. There. We told you.
Quality optics make the image sharper. Inexpensive glass may produce images that are fuzzy or have little rainbows at the edges. Superior glass produces edge-to-edge sharp images.
When light enters or leaves binoculars about 5% is reflected. Because there are as much as 16 air-glass surfaces inside your binoculars, you need to coat each surface with SOMETHING or no light would get through! This is why, on good binoculars, all surfaces are coated. One or more coatings are applied, generally magnesium fluoride. There are sometimes several coats. These can appear as violet, blue or green tints when you look into the objective lens. Amazing light transmission efficiency can be achieved in this way.
These are the clever optical devices that invert/reverse and fold images so that what you see in the eye piece (ocular lens) makes sense to you. Prisms shorten the binoculars, otherwise you would be looking down a stereo telescope!
There are two types of prisms, but the most common is called a PORRO. The other is called a ROOF prism. They both come in two types of glass, BK-7 and BAK-4. BK-7 uses boro-silicate glass and BAK-4 uses a denser, finer barium crown glass. BAK-4 is best and this reflects the more expensive models.
The other big compromise (apart from brightness) with binoculars is how wobbly the image gets. When you look through a telescope, or a set of binoculars you are amplifying the image that you want to see at the expense of background. This narrowing of the field of view is the price you pay for the up-close views of what you want to actually look at. In order to get a good stable image you need to stabilise yourself so that the binoculars don’t move around. This can take practice. Generally, on a boat you will need to brace yourself unless the boat is rocking severely.
If you have enough money, you can now buy image-stabilised binoculars. They electronically stabilise the image. So you can get, say 18xmag and a stable image. Once you have looked through a pair of these you WILL want a pair.
In a damp marine or camping environment with possible high humidity as well, you really should invest in waterproof models. The only time that non-waterproof binoculars are safe is in a highly controlled environment such as a house where the binoculars never leave the premises. (in this case you would look out of a window or off a covered balcony.)
Non-waterproof binoculars frequently “fog-up” and need to be left for hours out in the sun on a dry day (the hotter the better) to get rid of the moisture. Even this only partially works.
In waterproof construction all moving surfaces are o-ring sealed. The gas inside the binoculars is generally nitrogen that has been completely desiccated, i.e. dried out. The nitrogen is frequently lightly pressured compared to outside air pressure to further prevent damp ingress.
This is the maximum distance from the eye piece (ocular lens) to your actual eye, which still allows a full field of view. If you wear eyeglasses or even sunglasses when using binoculars, this is an important number. Look for at least 10mm (3/8”) of eye relief. Some cheap binoculars do not have this and you can have a miserable time trying to get a proper view.
Generally, there is a tubular knob in the centre of the binocular frame. This knob actually focuses the image. Before using this knob, one eyepiece can be adjusted for the slight focal difference between each eye. Get the both-eyes-open focus first, then adjust the central knob which adjusts both sides simultaneously.
Some binoculars have a built-in compass which is either on the top of the frame of the binoculars or actually superimposes a compass bearing on the actual image. This can be very handy on a boat.
Another feature of up-market binoculars is a Rangefinder reticule. This enables you to mark an object in the distance (say a mountain or lighthouse etc.) If you know the height of the object (from a chart) you can measure the angle (from the Rangefinder reticule) and then calculate the distance to that object.
Image stabilising binoculars come in two types. Gyroscopically stabilised and “electronic” stabilisation. The electronically stabilised units feature
piezo vibration and position sensors or gymballed prisms with servo control (really electronic/mechanical.)
The gyro-stabilised are very expensive, typically $8-10k. The piezo type start at about $1200
They all work astonishingly well and give clear, steady images with no-loss magnification up to 14x.
IF YOU HAVE THE MONEY AND YOU ARE A SERIOUS BOATIE, THESE ARE FOR YOU.
|LIGHT TRANS EFF.
|EYE RELIEF (MM)
|FUJINON “MARINER WP-XL”
|FUJINON “MARINER WPC-XL”
|Broad Field of View
|NIKON PROSTAFF 7S
|NIKON MONARCH 5
|NIKON MONARCH 5