A binoviewer is a device that splits visual input from a single objective into two viewing windows. A common example can be seen with the laboratory microscope, which collects visual information from the microscope stage with a single tube, but splits it into two eyepieces for the user. These devices are also sometimes used in astronomy, where they are fitted to telescopes to enable binocular viewing. Numerous optics firms sell binoviewers and accessories for the benefit of their customers.
The primary advantage of a binoviewer does not have to do with the optics. It involves the eyestrain associated with using a single objective for viewing. Many people are accused to binocular vision in daily life, and find the use of a single lens uncomfortable. Prolonged use of a tool like a spyglass can cause eye strain and discomfort. Binoviewers split the input into a format that may feel more comfortable and familiar.
When people look into the binoviewer, they see the same image in both eyepieces. It is usually necessary to adjust the eyepieces to avoid the appearance of a split image. They can be rotated on an axis to allow the user to bring the split images together into a single field that resembles regular vision. Focusing sharpens the image, and it may be possible to focus the eyepieces separately to fine tune them, for a user with visual acuity issues.
Looking through one eyepiece of a binoviewer alone, the user may note that the image can appear fainter than the combined view. This is a result of the mirrors used to split the original image in two. Users can adjust lighting and contrast on the device to get the crispest, clearest possible image. Some equipment, like telescopes, is capable of saving settings for the user. This can be helpful for shared tools where people want to be able to quickly and easily return to the viewing settings that are most comfortable for them.
It is possible to purchase binoviewer attachments for telescopes, microscopes, and other equipment. These can be specific to the manufacturer, as different optics companies use their own proprietary technology. People who are unsure about whether a splitter will work with a given device can contact the manufacturer to discuss the technical specifications. Some sellers also have generous return policies to allow customers to buy items to try without an obligation, in the event the optics aren't comfortable to use or don't work with the buyer's equipment.