When describing binoculars what do the figures 10X21 or 18X21 mean - I have been told that the first figure is the magnification and the second is the diameter of the front lens. Please could you tell me if this is right? Thanks, Fred.

Spotting Scope is a type of telescope typically used for observing wild animals and birds. A spotting scope features more magnification than a conventional binocular but less than an astronomical telescope.
The utility of a spotting scope becomes most obvious when the identification of an animal going in a large herd is required. Figuring out a specific animal from other look-alike animals becomes easy with such a device. For digiscoping purposes, few things can beat the power of spotting scopes. It is possible by using binoculars or telescopes to take a closer look at birds or other animals, but if you want a precise view of your target animal, a spotting scope is preferable.
Spotting Scope Features Explained

• Objective lens
  Objective lens, also known as the Front lens, determines the image quality at higher magnifications. The diameter of this lens ranges from 50-100mm in size. It is also called "Aperture" of the lens. It is wise to buy the highest size of the objective lens considering its weight. Larger lenses allow to pass more light and create more bright images. This means you will get higher image quality with the larger lenses.
• Lens Coating
  Manufactures often apply the chemical coating, which is known as Lens Coating, on the lens to reduce noise and increase light transmission. They also offer "fully coated," "multi-coated" and "fully multi-coated" lens to improve image quality. The premium quality spotting scopes' lenses are multi-coated with multiple layers on the surface.
• Focusing
  There are two types of focusing mechanism in the spotting scopes such as Helical and Knob focusers. The focusing characteristics determine how quickly you can focus on the object with maximum precision. Between these two options, the helical focuser is the finest option for birding as it can change magnification rapidly along with the movement of the bird. For hunting or spotting slower animals, Knob focuser is best as it gives you more precise information than the former one.
• Eye relief
  The eyepiece remains at a little distance from the users' eyes. This distance is called the eye relief where the light rays transmitted from the object pass to enter into your pupil. The comfortable eye relief distance is about 15mm to see the full field view. This feature is very important for those who wear eyeglasses. Nowadays, manufacturers are offering long eye relief for those who need to wear eyeglasses for convenient viewing.
• Image Quality
  You might have seen some designation on the glass label of the spotting scope such ED glass, APO glass, HD glass, Fluorite glass. These special qualities of glass will cost you more but create a huge difference in image quality comparing low-quality lenses. Remember, you must pay for the good quality images when it comes to buying any types of optical instruments.
• Magnification
  The magnification of spotting scope is higher than standard binoculars and varies between 15x to 75x. The power of the eyepiece determines the magnification of the scope. The important fact you should know that image quality drops off as the magnification goes up. Even premium quality scopes also lose a little quality at the highest magnification.

The condition of the atmosphere has effects on birding, hunting and digiscoping too. Humidity, ever-moving air, dry climates, dust and so on hinders the magnification and image quality at large.

Optical field of view (FOV) refers to the width of the area that you can see when looking through a pair of Binoculars or a Spotting Scope, quite simply, how wide an area you can see through your optics. Field of view is usually described in terms of 'linear field of view' or 'angular field of view'. Both figures essentially indicate that the field of view of the optic is a certain width, but they just use different numbers to describe this.

Linear field of view is also known as the true field of view and indicates the width (in m) of the area that you can see when standing 1,000m away from an object.
Angular field of view is also known as the apparent field of view and refers to the true angle (in degrees) seen through the optics.
It is easy to convert between the two field of vision measurements:
To convert an angular field of vision to a linear field of vision, simply multiply the angular field of vision by 52.5.
To convert a linear field of vision to an angular field of vision, simply divide the liner field of vision by 52.5.

When choosing your binoculars or spotting scope, take some time to consider where you are planning to use them, as this will indicate the most suitable field of view required to get the most out of your product. The most important thing to remember is that the larger the number is given to the field of view (FOV), the larger the width of the area you will be able to see through your scope. A larger field of view is desirable if you are planning to use your scope to watch anything that is moving quickly across your viewing area as it will make it easier to aim and stay on a moving subject. For this reason, scopes with a larger field of view are favored by people watching birds in flight, a ball at a cricket game, an athlete in a race or views from a moving car.
Don't forget field of view (FOV) and magnification are closely linked, with higher magnifications resulting in a smaller field of view. Take some time to consider whether you wish to view your subject in great detail, or would prefer to be able to keep track of it if it is moving quickly; after all, there's no point being able to see the fine detail on a bird's feather if you can't find the bird in the first place!

thats how binoculars are. Yours in this case is really strong. the closer you are to something, looking at it, the more magiflyed you going to be. try view things far a distance, really far away. no more double right?
Everything you need to know to become an expert:
on this website: http://www.chuckhawks.com/binocular_basics.htm
It is surprising how many people do not know how to focus binoculars correctly. There are two common focusing systems used in binoculars.
The first is individual eyepiece focus. This system is simple to understand, and easy to manufacture. It also lends itself well to sealed optical tubes, and thus is usually the focusing system used for waterproof binoculars. Individual eyepiece focus means that to focus the binoculars to your eyes, you simply focus the left eyepiece to your left eye and the right eyepiece to your right eye. There is no centrally located focusing mechanism. It is done like this. Look at something in the distance. Close the right eye (or cover the front of the right binocular), and focus the left eyepiece to your left eye. Close the left eye (or cover the front of the left binocular), and focus the right eyepiece to your right eye. You are finished, until you need to look at something at a different distance, in which case you need to repeat the process.
Because individual eyepiece focus is time-consuming, center focus is more common. Unfortunately, very few people understand how to correctly use center focus binoculars. Here is how it is done. Aim your binoculars at something in the distance. Close the right eye (or cover the front of the right tube), and focus the left side of the binocular to your left eye using the center focus control, which is concentric with the pivot shaft between the binoculars. (Note: the left eyepiece itself does not focus on center focus binoculars.) Next, close your left eye (or cover the front of the left tube), and focus the right eyepiece to your right eye. DO NOT touch the center focus control while you are focusing the right eyepiece to your right eye. Now you are finished. What you have just done is adjust the binoculars for your individual eyes. (Practically everybody's left and right eyes are different.) From now on, you only need to adjust the center focus control when you look at things at different distances. Center focus is faster and easier to use than individual eyepiece focus, once you have initially set the binoculars for your eyes.
Binoculars are commonly described by using a pair of numbers, as in "7x50" or "8x25." The first of these numbers refers to the magnification offered by the binocular. Magnification is why most people buy a pair of binoculars. In the examples above, "7x" means the binocular makes whatever you look at appear seven times closer than it does to the unaided human eye. "8x" means the binocular makes whatever you look at eight times closer than the unaided human eye. "10x" makes things look ten times closer, and so on. The first number used to describe binoculars always refers to their magnification. Common binocular magnifications are 6x, 7x, 8x, 9x, and 10x.
There are also variable power (zoom) binoculars, such as 7-21x50. These almost always perform much better at the low power setting than they do at the higher settings. This is natural, since the front objective cannot enlarge to let in more light as the power is increased, so the view gets dimmer. At 7x, the 50mm front objective provides a 7.1mm exit pupil, but at 21x, the same front objective provides only a 2.38mm exit pupil. Also, the optical quality of a zoom binocular at any given power is inferior to that of a fixed power binocular of that power. In general, zoom binoculars are not the bargain they seem to be.
Remember that everything (including movement) is magnified when you look through a pair of binoculars, especially your own shakes and tremors. So the higher the power, the harder it seems to hold the binoculars steady. 6, 7, or 8 power binoculars are easier for most people, even those with very steady hands, to hold reasonably still. The higher powers sound like a good deal, but often result in jiggly, blurred views. This is why 7x binoculars are chosen by so many experts, including the military.
Power affects brightness. Other things being equal, the higher the power, the dimmer the view. And power also affects the field of view of the binoculars. Again, everything being equal, the higher the power, the smaller the field of view. So, as you can see, power must be balanced against other desirable characteristics when choosing binoculars.

18 power magnification, and the second number is aperture 21mm or how big the main lens happens to be--

But your two numbers do not make any sense. No one sells an 18 power 21mm binocular.

Usually something like 10x50mm.

The numbers on binoculars in the form 00x00 are the power and the diameter of the objective (the main lens). A common one is 8x30, for small binoculars of 8 power and an objective 30mm in diameter.

10-30x60 is a bit more complicated. The diameter of the objective is 60mm, but the first numbers with the hyphen indicate a range of powers, from 10 to 30, because these binoculars have a zoom feature, giving variable power.

In my view, zoom on boinoculars is a gimmick. It isn't useful in practice, usually giving too much magnification to be useful at the high power end, and the complication it adds to the optics means that the image is not as good as with simpler binoculars of similar quality.

Because of the magnification any unsteadiness in your hands is multiplied. Try to brace your elbows or put the camera on something steady. About 1/2 second after you click the button is when you hear a little beep. That's the moment you ahve to hold the camera very still.

Also, I wear glasses with a strong correction, I get better pictures when I take them off to focus the binoculars.

Binoculars are often refered to as "N x NN" which typically refers to the magnification and the size in millimeters of the front lenses (called the "objective" lenses). 6x20 refers to 20mm front lenses (about 3/4 inch) with 6x magnification. These would be useful as opera glasses, or for spotting birds in a small backyard.

The "N x NN" designation doesn't say anything about the quality of the binoculars - just the physical size and magnification.

The first number is the magnification the second number is the size in millimeters of the objective (large lens) So if you measure the diameter of the front large lens that will give you the size. So a 10x50 means a magnifyng power of 10 and an objective of 50mm.
Now to find out the magnification if you don't know what it is. Measure the front lens. Then if you look through the eyepiece lens while holding it away from you you will see that there is in each a small circle of light. That it what is known as the exit pupil. It lines up with the pupil of your eyes when you have the binoculars pressed up against your eyes. Now measure the diameter of the exit pupil in millimeters. It will only be a small number.

To work out the magnification use this formula. Magnification = Objective size divided by the exit pupil.
So a 10x50 will look like this M = 50 divided by 5....therefore M =10 which is the magnification.

Both the 7x35 and 10x50 will have an exit pupil of 5mm. So if yours is one of these then all you need is the objective (large) lens size.

these binoculars were made for astronomy or day viewing but are hard to hold steady by hand, best to use tripod...bak4 prisms means you should get a sharp image from edge to edge, in cheaper models with cheap prisms only the center of the field of view is [email protected]

you have this car posted under binoculars, not cars.