Posted by Elke Naber on 23rd Apr 2020

14 Main specifications of Binoculars

Are you looking for a new pair of binoculars but you don't understand all the specification terms? We understand that very well, because they are very difficult and sometimes need a little more explanation. Especially if you want to make the right choice. That is why we give you an explanation of the 14 most important specifications of binoculars.

CONTENT

  1. Magnification factor
  2. Front lens diameter
  3. Twilight factor
  4. The exit pupil
  5. The light intensity
  6. Twilight or light?
  7. Eye distance
  8. Dioptric correction
  9. Field of view
  10. Depth of field
  11. Type of glass
  12. Coating
  13. Type of Prism
  14. Nitrogen filled

1. Magnification Factor

Each Homey’s binoculars has two numbers in its description, for example 8x42. The first number is the magnification factor, so 8 in this case. This means that when an object is 80 meters away, you see it 10 meters away through your binoculars.

It may be attractive to use the largest magnification factor as possible but this is not the best choice. This because the vibrations in your hand are also magnified. When these movements become too large, your brain can no longer correct this.

In addition, with a too large magnification factor you can’t focus on things that are close to you. Your focus point is much further away. Take this into account when choosing your binoculars, plus that especially the binoculars with a larger magnification factor are usually the more expensive ones.

The magnification factor also has a direct link with the exit pupil (4), the twilight value (3) and the relative brightness (5).

2. Front lens diameter

The second number in the description of 8x42 is the number which indicates the diameter of the front lens. The larger this number, the more light is received by the field glasses. If you want to use your binoculars in dark conditions, make sure your diameter is large for a lighter image. Binoculars with a large diameter are often a lot bigger themselves.

The magnification factor (1) and the diameter of the front lens (2) are used to calculate the twilight number (3), the exit pupil (4) and the brightness (5) of the binoculars.

3. Twilight factor

The twilight value is a number that indicates how many details you see in dim lighting conditions. The rule for this is, the higher the twilight factor, the more details you see in twilight (reduced lighting conditions). Field glasses with a twilight number under 15 are suitable for daytime use, binoculars above 15 are often used for lesser lighting conditions.

The twilight factor is calculated as follows:

root (magnification factor x objective diameter)

4. The exit pupil

Also important is the diameter of the exit pupil. This indicates the size of the light beam leaving the binoculars. It must be larger than your own pupil, if it is smaller than the pupil of your eye, it is more difficult to get a good picture. The exit pupil can be determined by dividing the diameter of the objective lens by the magnification factor. With an 8x42 binoculars, the exit pupil is therefore 42/8 = 5.25 mm.

The less light, the more you will suffer from a small exit pupil. This is because your pupils enlarge in low light. The pupil size varies from 2 to 7 mm, so you know that an exit pupil larger than 7mm makes no sense.

Calculation of the exit pupil:

Lens diameter / magnification factor

5. The light intensity

In addition to the exit pupil, the brightness is also determined by the light intensity. This is very simple to compare, the higher this number, the better the quality of the binoculars. Under 15, the binoculars are suited for daytime. Field glasses with a high light intensity (7x50, 8x56, 9x63) are also known as night viewers.

Calculation of the light intensity :

The square of the exit pupil

6. Twilight or light?

When you look at the different calculations, the following conclusion is useful: The diameter of the front lens has a positive relationship with the twilight factor and the light intensity. This means that as the diameter of the front lens increases, both the twilight figure and the light intensity improve.

This is different for the magnification factor. A higher magnification gives a higher twilight value but a lower light intensity.

It really depends on where you will use the binoculars. For example, in Europe you have a lot of twilight time, so the twilight value of your binoculars must be higher. But when you go to the tropics, you need binoculars with a higher light intensity or brightness.

The light intensity can also be improved by using special glass types or coatings. The geometric brightness, therefore, says nothing about the actual brightness of binoculars.

7. Eye distance

The eye-distance is the distance from the eyepiece to the eye. This is an important fact for people who wear glasses. They will need a much larger distance than people without glasses. With some binoculars you can determine this distance yourself – by means of adjustable eye caps – but with some it is fixed. Eye distance for people who wear glasses is comfortable from 15mm.

8. Dioptric correction

People who wear glasses can also choose to take binoculars for which they do not need glasses. This is made possible by the dioptric correction and the focus, so that the correction that is normally in the glasses now takes place in the binoculars. The two eyepieces would be adjusted independently. This means that you have to take off your glasses when you look through the binoculars and you should reset this every time you wear your lenses. This is a matter of what do you prefer.

9. Field of view

The field of view narrows as your magnification increases, but this too depends on how the viewer's eyes work. The magnification will reduce the overview you have. The number in the field of view indicates the diameters in meters that you can observe horizontally at a distance of 1000 meters. When it is larger, you can "find" something faster and also better track an object.

10. Depth of field

The binoculars can be set with a sharp point. Unfortunately, everyone will experience this differently because you are dealing with the natural experience of sharpness. With this natural experience, people have the perception of sharpness with a slight degree of blur, this is called depth of field. The depth of field differs for everyone and will therefore sometimes cause some discussion of the binocular settings – I was never allowed to touch my grandfather’s binoculars.

This difference will decrease when a subject is displayed larger. What can happen as you have a larger magnification factor, or when you simply move closer.

11. Type of glass

The type of glass that is used for the lenses of binoculars also makes a difference. There are differences in BK-7 and BaK-4 glass, both with pros and cons.

BK-7 glass is made of crown glass and has a very high refractive index. This index ensures that you get a good and clear image, which is of course very important with binoculars. This glass is easier to make than BaK-4 and therefore cheaper.

BaK-4 glass is made of barium crown glass, which has an even higher refractive index. This glass will give a better picture than binoculars with BK-7 glass. It is also more difficult to produce and is therefore used in more expensive variants.

12. Coating

When we talk about coating, it is not about the possible nice print that the housing has, but about the processing of the glass through which you look. Untreated glass can reflect 5% of the light, so you will lose a lot of light with all the glass you look through. A layer with an anti-reflection coating can already reduce this loss by 1.5%. This loss can be improved with multiple layers up to 0.2%.

The coating can also ensure that an image can be displayed with a higher contrast. You will notice this due to the differences in coatings with somewhat higher-priced binoculars and the lower-priced ones. In the lower class there will be a somewhat pale image and possibly a color cast.

13. Type of prism

The difference between a Porro or a Dakkant binoculars is on the inside, but you can also see the difference from the outside because of its size. With porro binoculars, the light passes through the viewer in an N-shaped bend. The disadvantage is that it is less compact, but because this technique is easier to make, it is often cheaper.

The Dakkant binoculars are a lot narrower than the Porro ones, because the light can pass directly through the viewer. This system makes the binoculars a bit more compact, but because it is more difficult to make, these binoculars are often more expensive.

14. Nitrogen filled

When making binoculars, you can choose to make the binoculars airtight after a rinse with dry and dust-free nitrogen. This ensures that the binoculars remain free of condensation and dust. Also, by leaving a slight overpressure of nitrogen, this can make the binoculars waterproof.

CONCLUSION

The perfect binoculars unfortunately do not exist, but personal favorites do. In the search, make sure you have clear what you want to focus on, what you need the binoculars for and base your choice on that.