If you really want to go even smaller and lighter than the smallest and lightest pocket binocular, but still have something you can use to see an object you can’t see with your own eyes, the way to go is monoculars. These incredible little instruments can do what a pocket binocular can do, but with only one telescope and not two like all binoculars. You use only one eye, since the instrument has only one ocular lens and one objective lens.
They have virtually the same specifications as a binocular: magnification, objective lens diameter (aperture), exit pupil, field of view, etc. and it can also focus on any object from a certain distance up close to infinity. Basically it is a telescope or spotting scope, but only very small and very lightweight – some only 3 inches long and weighing 5 ounces!
So, if weight and size are REALLY an issue, consider a monocular!
What are the advantages of a monocular?
Simplicity of design: Comparing a monocular with a binocular, one will immediately realize that the design is so much simpler. Simplicity has a lot of benefits: No collimation issues (perfect alignment between the two telescopes of a binocular), no diopter, and weatherproofing much easier.
Cost: Since monoculars are only half that of a binocular, they are considerably cheaper. This means that you can buy into technology which you may not be able to afford (or be willing to pay) in the case of a pair of binoculars.
Size and weight: Size: Any monocular easily fits into any pocket – most of them even in something as small as a purse. Weight: Since a monocular is merely half of a ordinary binocular in size, that goes for weight as well. They are really lightweight – some weigh even less than 6 ounces. The popular Zeiss 10×25 T Monocular (see review) only weighs an incredible 3.1 ounces! This means that you can always have a monocular at hand – in particular when you will not be carrying a binocular. This makes them very inconspicuous as well.
Objective lens diameter: Since size is no issue at all, they have one huge advantage above all pocket binoculars: The objective lens of a monocular can be as wide as 40 mm, like the Barska Blueline 10×40 Close Focus Monocular, and still easily fit into any pocket. The wider lens brings a lot of advantages, among which higher relative brightness.
Close focus: Some monoculars can focus as close as a few inches, which is excellent when you’re into small stuff like butterflies. The Zeiss 8×20 T Monocular focuses as close as 10-14 inches! (see review). They can even be used as field microscopes .
Two negative points:
Using only one eye in long viewing sessions is more tiring than using two eyes.
Monoculars produce 2-dimensional images, while binoculars add perception of depth.
Monoculars will never replace binoculars, but should be considered a handy addition which could be considered to supplement your main instrument. Think about all the advantages they bring to the table.
For an overview of the most popular monoculars, please go to Monoculars: The most popular models.