Naturalists, Bird-Watchers, Astronomers, Wardens, Fire-Watchers, Coastguards, Yachting Club Members, Executives, Estate Managers, Security Staff, Hotel Guests, etc. In short, anyone enjoying or overseeing a vista or view.
Why big binoculars?
Big binoculars, generally known as observation binoculars, are those with objective lenses of diameters of 70mm and upward (to 150mm). They are generally used for long-range terrestrial observations or astronomy over a long period of time when the use of both eyes is more comfortable than using a telescope. The use of large objectives results in a large binocular, which necessitates the use of a good tripod for reasons of weight and to hold them steady under high magnifications. Using large objective results in great light grasp, the practicality of high magnifications and better resolving power and so long-range study of detail is improved.
There is more. Larger objectives allow the use, with minimal errors, of long focal lengths. The longer the focal length of a lens (distance from principal focus to the lens), the less the light rays are refracted (or bent) and the less colour dispersion occurs. Also, depth of field (the amount in focus at one time) generally increases with increased focal length.
Miyauchi 20 x 20 (45 Deg.)
Thus, if we compare, say, a Miyauchi 100mm binocular with a less expensive Sentinel 100mm one we find the performance of the Sentinel binocular greatly benefited by its longer focal length whereas the Miyauchi binocular achieves good results in a more compact form by even higher manufacturing accuracy (at a price) and also by offering an APO (apochromatic) version for maximum colour correction. The Sentinel binoculars come in a semi-APO design and the reason these binoculars are larger is due to the need for larger prisms to “compact” the light paths of the longer focal lengths. Everything in optics is a compromise somewhere along the line and relies much upon the designer’s art.
In general, observation binoculars are sturdily built to maintain collimation (optical alignment) of the two sides, which becomes more difficult to maintain as the power is increased. Needless to say, such binoculars need very sturdy tripods to obtain the best results. Sentinel 100mm binoculars come with a custom-made tripod but, for the rest, we recommend the use of an Italian-made Manfrotto tripod such as the 055/NAT with fluid head or the even more solid 501/344B.
The origin of big observation binoculars was with the military which used them for the early spotting of enemy ships and for artillery spotting but much of this duty is now carried out with the use of satellites and electronics. Another case of “swords into ploughshares” with civilians benefiting. Because of the outdoor environment in which these instruments are often used, they are often filled with nitrogen to prevent fogging from moisture and to prevent long-term oxidation of the optics. Such an instrument is also dust-proof, of course, and uses independently focussed (IF) eyepieces as opposed to centre focussing (CF) instruments.
To sum up, BIG BINOCULARS give you:-
a) Better light grasp (increases as the square of the diameter).
b) Higher resolution (increases directly as the diameter).
c) Opportunity of high magnifications while using both eyes (for comfort and long-term viewing).
d) Long focal lengths to minimise colour dispersion and improve depth of field.
