Steiner Merlin 8x42 roof prism binoculars

Good birding binoculars are clear, powerful, rugged, easy to hold and simple to focus. Bird watchers have to be very particular about the binoculars they use, because they not only must spot birds but also identify them. This requires a clear sharp view such that fine details can be observed. Birds can be observed in all types of environments, at all hours of the day and in every kind of weather condition. Many times the view of a bird is just a fleeting glimpse, meaning that the quality of a very short look can determine whether or not an identification can be made. The birding binoculars must be able to deliver the best view possible in all conditions, especially in low light. You also want binoculars that you can use for long periods of time without causing eye strain.

Depending on your budget, the basic considerations for choosing a good pair of birding binoculars are: image quality, magnification or power, close focus distance, eye relief, brightness, ease of use, handling, durability and weather resistance. The design, quality of materials and manufacturing factors are also important. Because individual needs vary between birders, there is no one binocular or type of binoculars that is best for everyone.

Quality & design: Quality of optics increases with price, until the very top of the line where price goes up sharply. High-quality optics have multi-element lenses with several coatings to optimize the visible light spectrum, very close tolerance manufacturing and the best consistency and alignments available. To get the best performance there is no way around the expensive, top of the line products. On the other hand, the mid-range optics may not have quite as many lens elements, features, and options, but are still fine optics with slight differences in viewing ability under most situations. That said, you get what you pay for in optics, especially in low-light conditions. High-quality optics perform well in all conditions, deliver the sharpest image with the truest colors and have ergonomic designs that maximize comfort during use. Even with the best optics, there are many considerations, choices and some trade-offs that will be determined by each individual's needs. There is no ideal pair of binoculars on the market, and the choice has to be made by what you want from them, the conditions under which you will be using them and what you can afford.

Porro & Roof Prisms: Birding binoculars use prisms to present an upright image to the viewer. There are two main designs - the porro prism and the roof prism. Porro prism was the first of these two designs and consists of two mirrors mounted separately. The roof prism is a more modern design that consists of two prisms cemented together in a single interior mount. In both designs, light passes through objective lenses that cast it onto a set of mirrors that flip, rotate and focus the image through an eyepiece and into our eyes. Porro prism binoculars are larger and bulkier than roof prism ones. Roof prisms, because of the engineering required, are more expensive than porro prisms of equivalent optical quality. Porro prism binoculars reach very good optic quality at about Rs 15,000. Roof prisms do not reach an equivalent level of optical quality until over Rs 25,000. Porro prism designs tend to be more susceptible to alignment problems if dropped. Roof prisms designs are internal focusing and that makes them more durable and weather resistant.

Magnification: Binoculars are labeled with numbers that refer to their magnification power and size of their objective lens. These numbers are written as 10 x 50 or 8 x 42.The first number refers to the magnification. This means the view that is seen is that many times as large as with the normal eye. If this number is hyphenated it means that the binoculars are capable of a range of magnifications (zoom). Full size birding binoculars generally range from 7x to 12x, the more popular being 8x and 10x. Generally speaking, with increase in power there is a decrease in image brightness, image stability, and field of view. Adults with steady hands do well with 10x binoculars, while older people and children find 7x or 8x more suitable. Binoculars over 10x power are difficult to hold steady enough to see the image clearly, and require tripods.

Size of Objective Lens: The second number represents the size of the objective lens in millimeters. The larger the objective lens the more light it allows into the binocular and the brighter and clearer the image will be. Of course, the quality of optics, power of magnification (more magnification = less light) and how stable the optic is mounted, will determine the overall image quality. As objective lenses get larger, the optics get heavier and more uncomfortable to hold. Practically, a 50-mm objective lens is about as much as anyone would want to carry in a binocular with today's materials. Because of the weight, people will often opt for 42-mm objectives. In good daylight a 35-mm objective is able to deliver all the detail we need. But a larger objective is required for overcast days, bird watching in shadows, in the woods, and in failing light.

The Exit Pupil: Another factor in choosing binoculars for bird watching is determining the exit pupil. Ideally binoculars' exit pupil should be 4 mm or above for general daylight use, or 6-7 mm recommended for low light work. To determine the exit pupil of a pair of binoculars, divide the size of the objective lens by the magnification. In the non-zoom example above we would divide 35 by 7 and determine that these binoculars have an exit pupil of 5 mm, a good size for general work. (The exit pupil is the diameter of the image as it leaves the eyepiece lens. If it is as large or larger than your eye's pupil diameter then your eyes can take full advantage of the images they receive. If the exit pupil is smaller than your eye's pupil diameter the image may appear dark and less clear.)

Eye Relief: Yet another important consideration, especially for those of us who wear glasses is eye relief. Eye relief is the maximum distance in millimeters that your eyes can be away from the eyepieces and still see the whole picture. Normal binocular eye relief ranges from 9 to 13 mm. This distance works well for people with good eyesight. Most glass wearers need eye relief over 13 mm. Binocular manufacturers try to provide this relief through the use of rubber eyecups that can be rolled down. Often this is not enough! Some binoculars are constructed with extended eye relief for glass wearers. Many manufacturers add the letter AB@ the description of binoculars with long eye relief.

Close Focus Distance: Birders need close focus to study birds up close. Well designed modern binoculars are able to focus as close as 2.5 m, and this is one of the important considerations while choosing a new pair of binoculars.

Field of view, size, weight, and cost are other factors to consider, but that's an individual choice and is hard to predict. Getting good magnification and clear, bright images are very important, however. The best way to test for what's comfortable for you is by trying different binoculars before you buy them, either at the store or preferably by borrowing them from a friend. The binoculars should also be tested for image brightness in fading light and bad weather. A good, economical choice would be a well-made set of 8 x 42 or 10 x 50 porro prism binoculars. If your budget cooperates, consider higher-priced binoculars which tend to be more ruggedly made, have better optics and cause less eyestrain.