Binoculars Info

wesley c asked:


I want to know how to use binoculars to calculate the distance from me to an object.

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When buying binoculars for astronomy one of the main considerations is the light gathering capability of the binoculars you are looking to buy and therefore the size of the objective lens is extremely important.

Before you start check out the range of binoculars for astronomy that are currently on the market you need to consider the distance you are looking to cover and what level of detail you are hoping to see. If you can imagine that a telescope can provide you with a significantly larger aperature (objective lens) and a wide range of magnification abilities it’s understandable that for viewing over longer distances, and to see the finer details, a telescope is often a better option. However that said binoculars can prove useful, even for the serious astronomer, and are an inexpensive way to get started.

The real pro’s of using binoculars for astronomy is the minimal set up time, the relatively low cost, portability and the fact that there isn’t an endless list of accessories that you need to buy.

Manufacturers generally indicate whether or not their binos are suitable binoculars for astronomy but as a general guide you want to be looking for giant binoculars or binoculars with an objective lens that is 50mm or greater. 10×50′s are often a popular choice for astronomy as they are reasonably comfortable to hold yet powerful enough for the basic astronomers needs.

Some manufacturers do make smaller binoculars for astronomy such as the Pentax PCF 8×40 or the higher quality Pentax DCF SP 8×43 and Olympus rate their EXPS I 8×42′s as excellent astronomy binoculars. As a general rule, and particularly relating to the smaller binos, if the objective lens is 5 times or more than the magnification you can use them for astronomy.

If you are looking for a real meaty beast then the Celestron Skymaster series ranges from 15 x 70 up to 25 x 100 (which offers the power of a small telescope) and Nikon do the 10 x 70IF SP which is considerably more expensive (around £1200 versus up to £400 for a Skymaster) but you are paying for the quality of the lenses and the superior optical design (one of the leaders in it’s class). The bigger you go when you are looking for binoculars for astronomy the greater the power and light gathering abilities so if you opt for a 25 x 100 (25x magnification, 100mm objective lens) you will be able to see further and view objects in greater detail than with a 7 x 35 or a 10 x 50 (for example).

Binoculars for Astronomy, quick check list:

• Fully multi-coated lenses are a must

• Waterproof binoculars are generally best if you want to prevent fogging and view in all weather conditions.

• The best astronomy binoculars come with Bak-4 Porro prisms (Bak-4 glass is high quality glass and porro prisms generally provide greater light transmission and a sharper image than their roof prism counterparts)

• Always check a binoculars suitability for astronomy

• Remember the more powerful the better and if you want a performance similar to a small telescope buy a binocular with the largest possible objective lens.

• For larger binoculars make sure you check tripod / mounting requirements.

• Quality optics is important and no more so than for astronomy. If you can afford high quality binoculars they are well worth paying for.



By: Terry Ross

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Optics workers will tell you they are often asked to recommend the best binocular for birders (bird watchers) To match the binocular to the birder it helps to first look at the needs of the birding enthusiast.

What sort of optical demands must we consider? Well for one thing the birder need to see details like the patterns and color of feathers, often in dim light such as under a tree canopy or in twilight. They need good magnification so that they can easily identify birds at a distance and sometimes they will want to observe birds at very short distances so they want their binoculars to work for close focus observing too, maybe even down to just a few meters.

They need true color viewing so they can see everything as it really is colored and not with any tint or false color. They also need a reasonable field of view so they can observe birds in flight easily and be able to pick birds out from the surrounding trees.

They want the binoculars to be light enough to carry and hang on a neck-strap. Their binoculars should be light enough to hold comfortably for viewing and easy enough on the eyes to be able to use for long periods. Birders usually want their binoculars to be compact enough to pack in a rucksack. For observing from hides they often want to use their binoculars on a tripod or mono-pod so a fitting for these adapters is advisable. If their bird watching is in the wilderness then rugged construction and some element of waterproofing and fog-proofing is also advisable.

When looking at binocular specifications we usually pay most attention to the two numbers that define the basic specifications. The first number gives us the magnification factor, so an 8x binocular magnifies an image (brings it closer) by 8 times. The higher the magnification the more difficult it becomes to use the binoculars effectively due to the natural hand-shake which makes it difficult to keep the bird in view and also the smaller the field of view will be. For birding use, an 8x binocular is the most commonly used though in some circumstances enthusiasts will use higher magnification.

The second number in the specs tells us the diameter of the objective lens. This is important for two reasons, firstly the larger the diameter the more light is captured by the binocular so the clearer and brighter the resulting image. Secondly, the larger diameter also gives a larger field of view. In the birding world, the most popular objectives are 40mm and 42mm. Getting much higher than this makes the binocular a little too heavy and large.

Other important considerations are the quality of the lenses and prisms and the optical coatings used on those elements. These coatings reduce loss of light through reflection from the binocular and its internal components and they help to preserve good clarity and true color throughput. As a rule of thumb look for Fully-Multi-Coated (FMC) coatings for bird watching use. The specification for eye relief refers to the distance between the eyepiece and the eye. Those who wear glasses will need a longer eye relief to allow for the extra distance caused by the glasses being between the binocular and their eye.

Roof and Porro Prism designs refer to the two body styles of binoculars. This difference comes about through the placement of the internal prisms within the binocular body. Roof prism types are the more compact and modern looking. Their objective lenses are more or less in line with the eyepieces, while porro prism types are the traditional style with the lenses stepped out from the line of the eyepieces. More and more birding enthusiasts are now opting for the roof prism type particularly as their quality has caught up with the porro types in recent years.



By: Aidan James

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