Close Focusing Distance | Optics Trade Debates

By Polona Kraner Jul 30, 2018

Welcome to Optics Trade debates. In each episode, we talk about a different topic and try to answer the most common questions we receive about it. Today we are going to talk about close focusing distance.

Close focusing distance is the minimal distance on which an image is observable. It’s important for close-up observations of butterflies, flowers… Most optical devices enlarge the image so that more details are visible.

The best central focusing binoculars can be focused on distances as short as 1m. When observing objects that are closer than the close focusing distance, the object is out of focus and the image is in two circles. Compact binoculars are especially good for close-up use.

Binoculars with individual focusing are really bad for close-up observation. Some can’t even focus images closer than 20 m.

Digital night and thermal vision devices have different focusing distances. Some devices are in focus at all distances and on others, the focusing is controlled by knobs. A short focusing distance is especially important for thermal devices which can be used for things like construction, electrical engineering…

It is also useful for hunting and observing animals that come really close by.

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Explanation of the term on our website:

Closest focus distance is an important value when watching butterflies, moths or plants at a really close distance. It represents the nearest distance where the viewing object can still be in focus. With binoculars, an excellent viewing distance is from 1.5 m below. If you’re not particularly interested in watching objects at a close range this is an irrelevant factor when choosing a new pair.