Binoculars are essentially two telescopes joined together to allow both eyes to view an enlarged image simultaneously. The ones illustrated are designated 8×30. They have a magnification of eight times, so that the object being viewed appears to be eight times closer. There are models with larger magnification, but anything larger than ten times is likely require a tripod as the image will be shaking. The 30 refers to the diameter in millimetres of the front lenses which collect the light. The larger the lenses the brighter the image will be. Larger binoculars need lenses wide enough to collect sufficient light for good viewing, but less powerful ones such as the 8×30 should be sufficiently bright and useful for general use when out and about. For stargazing or serious birdwatching more powerful binoculars are recommended. On the barrel next to the right eyepiece is an indication that the field of view of these binoculars is 8.2 degrees, approximately 430 feet at a range of 1000 yards. More powerful binoculars would have a narrower field of view. The binoculars featured have the original leather strap to hang them from the neck and reduce the risk of dropping them. They would originally have also had a protective case.
To use the binoculars the two barrels of the instrument need to be pulled apart from the folded position to bring the eyepieces into line with the eyes. The focus is adjusted by a wheel between the barrels, with a further adjustment, to allow for the difference in vision between eyes, made by turning the dioptre wheel by the right eyepiece. The image, which is projected by the light collecting lenses is upside down and mirrored. To correct this, inside each barrel of the binoculars is a pair of prisms.
These binoculars are branded Carl Zeiss Jena, model Jenoptem 8×30. Carl Zeiss is one of the most famous names in optical products. Carl Zeiss, an instrument maker, founded his workshop in 1846 and the firm produced their first 8×30 binoculars in 1920. One model, the Deltrentis, used individual focussing of the lenses and the other, the Deltrintem, had a central focussing wheel. The Jenoptrem model featured here is a development of the latter. It has multi-coated lenses, which means it was manufactured between 1978 and 1990, when production ceased.
The name Jena refers to the town in Germany in which the company was based. At the time of manufacture Jena was in the DDR – the Deutsche Demokratische Republik. Models of the Jenoptem binoculars made in Jena featured DDR in the name and bore the initials DDR above the company logo or elsewhere. At one time fake models were produced in Japan and this led to the Carl Zeiss company authorising a Japanese firm to make binoculars with the Carl Zeiss Jena name, but not featuring the initials DDR. The binoculars shown here do not have DDR markings and we must, therefore, assume they were made in Japan, not Germany.