Celestron Cometron 7x50 binoculars (SKU: 71198) giant binoculars opinie

Question: What do the numbers 10x25 / 10x50 / 7x50 / 20x60 / 20x80 / 8-20x50 / 10-30x50 given in the binocular name mean?

Answer: The first number in 7x50 is the angular magnification (7-times), and the second is the objective diameter in millimetres. A designation such as 8-20x50 or 10-30x50 means a zoom binocular with variable magnification – here from 8 to 20 times or from 10 to 30 times. 50, of course, is the objective diameter.

Question: Does the set include a case and a neck strap?

Answer: Yes, every binocular comes with a case and neck strap, and usually also objective and eyepiece caps, unless it is stated explicitly that they are not included.

Question: How do magnification and objective diameter affect the image in a binocular?

Answer: Higher magnification increases the visibility of fine details, but at the same time reduces surface brightness of extended objects. For hunting, magnifications between 7x and 10x are recommended; for birds and landscapes, typically 7x to 12x; for aircraft observation, larger magnifications of 15–20x or zoom binoculars are often chosen.
In turn, a larger objective diameter means higher resolution and a brighter image, but also greater weight and size, sometimes making a photo tripod necessary.

Question: I still don’t know which binocular to choose. I want a universal model with good parameters so that “you can see a lot”. What should I choose?

Answer: The most universal binocular parameters are 10x50, and this is what we usually recommend – such binoculars combine good detail visibility with high image brightness, a wide field of view, and do not require a tripod.

Question: Is it better to choose a binocular with fixed magnification or a zoom binocular?

Answer: Zoom binoculars contain an additional optical system that allows the magnification to be changed. In optics, “less is often more”. Every additional optical group that is not a dedicated corrector of an aberration generally has a negative effect on image quality. It is similar to photographic lenses – the most highly regarded lenses are usually fixed-focal-length designs, not zooms. On the other hand, zoom binoculars offer greater versatility, because few people carry 2–3 different binoculars with different magnifications.

Question: Does this binocular use glass objectives, or are they plastic?

Answer: All quality binoculars use glass optics only, because only glass can be precisely ground and polished to the required shape. Polymers (“plastics”) are limited by the accuracy of the moulds in which they are formed.

Question: The specification mentions anti-reflection / anti-glare coatings. What are they? Are they there so that I am not visible in reflections, e.g. from the Sun?

Answer: Anti-reflection (anti-glare) coatings are used to increase the efficiency of an optical system, for example a binocular, but in principle any optical instrument. Optical efficiency describes what percentage of the incoming light beam passes through the system. When light hits the boundary between two media, e.g. glass/air, part of the beam is reflected. From everyday experience we know we can see our reflection in a window – that is exactly the effect. To minimise these losses, anti-reflection coatings are applied so that more light passes through the boundary and less is reflected.
Anti-reflection coatings come in different types and qualities, and often they are what differentiates the best binoculars, whose overall efficiency can reach even 95%. The same type of coatings is used on the optical surfaces of microscopes, telescopes, spotting scopes, riflescopes, camera lenses, or night-vision devices, for exactly the same reason as in binoculars.

Question: In your descriptions you mention prism glass types BK7 and BaK-4. What does this mean?

Answer: Most optical prisms are made from BK7 (borosilicate) or BaK-4 (barium crown) glass. BaK-4 is a higher-quality glass which produces brighter, sharper images. It is also more expensive and is usually used in higher-end binoculars. This is worth considering especially if you are looking for binoculars for hunting or astronomy.

Question: I can’t find some parameters for this binocular that I’ve seen on other sites. Can I find out its brightness and twilight factor?

Answer: For clarity, we usually omit secondary parameters that do not add much information beyond what is already listed. However, you can easily calculate them yourself:
• the exit pupil is the diameter of the image-forming beam in the eyepiece; it equals the objective diameter divided by the magnification. For a 7x50 binocular, the exit pupil is 50/7 ≈ 7 mm; for 10x50: 50/10 = 5 mm; for 20x60: 60/20 = 3 mm. This parameter is usually listed in the description.
 
• relative brightness is the square of the exit pupil (in mm). For a 10x50 binocular, the 5 mm exit pupil gives a relative brightness of 25; for 7x50 it is 49–50; for 20x60 about 9 etc.
 
• the twilight factor is another secondary parameter often quoted for low-light hunting. It equals the square root of the product of magnification and objective diameter. With a basic calculator you can obtain:
- 8x40: 17.9
- 7x50: 18.7
- 10x50: 22.4
- 20x60: 24.5

Question: I’m looking for binoculars for astronomy. Which should I choose?

Answer: There is no single, simple answer. “Astronomy binoculars” are simply very good binoculars. This means very good correction of optical aberrations (mainly chromatic aberration and edge distortion) and high optical efficiency. For these reasons we generally do not recommend zoom binoculars for astronomy, with a few exceptions.
A binocular for astronomy does not need high magnification – that is the job of a telescope. A binocular should usually be handy enough to take with you whenever you cannot take a telescope – in that case 7x50, 10x50 or 15x70 binoculars are typical choices. Large binoculars dedicated to astronomy, such as 20x80 or 22x100, form a separate class of instruments and require tripod use.
For a beginner, an astronomy binocular serves to learn the sky, see star colours, and find the brightest deep-sky objects. For an advanced observer, a large binocular is a very efficient instrument for observing comets, variable stars, nebulae, star clusters, and galaxies.

Question: I’m looking for binoculars for a yacht / kayaking trip / fishing / the sea. What should I choose?

Answer: On the water, binoculars should be waterproof, nitrogen-filled, and have 7x magnification, as this is the only magnification that guarantees a bright and, above all, stable image on a moving platform.

Question: I’m looking for binoculars for birdwatching. Should I choose a high magnification (16x, 20x or a zoom)?

Answer: For birdwatching, we usually recommend fixed-magnification binoculars with low to medium power, i.e. from 7x to 12x. The optimal combination for a birdwatcher is a fixed-power binocular plus a spotting scope with zoom eyepiece on a photo tripod.