Baden-Powell's Unilens

The Unilens monocular is a simple device for field use, designed by Robert Baden-Powell (major of the british army), which allows the magnification of distant objects similar to a telescope. Occupying very little space it still can magnify a distant image about four times. The rudimentary nature of its lenses however does not accommodate to everyone's visual acuity - only three out of four people.[1]

Despite its limitations however, the Unilens monocular does improve the detail in viewing distant objects which are always in focus. Its small size and weight made it practical to carry in the field and permit viewing of unapproachable animals.[2]

Description and use

The "Unilens monocular" is simply a unique 2.5 inch convex lens fixed on a support (sometimes metal) which makes it the correct size to carry in a pocket. When needed, the metal mount can be clipped onto a wooden pole (similar to the "selfie stick" used for today's cameras), onto any kind of similar "pole" (trekking pole, etc..) or even at the tip of an umbrella.[3]

Original instructions advised the "Unilens monocular" user to sit with the arm holding the device resting on the knee and moving the lens forward and back until the desired object is in focus. Normally this would be about "4" feet from user's eye. The magnification increases as the distance from the eye increases although fully extended the image becomes slightly blurred.

An early newspaper description advised: "The maximum enlargement of the object achieved by holding the pole with the arm entirely extended (although, at the maximum distance, it may appear a small blur). The maximum working distance (adding the pole length), is equivalent to approximately "6 feet" from the lens to the eye (for a normal user)."[2]

See also

References

  1. ↑ Leathem, J. G. (2015-03-26). The Elementary Theory of the Symmetrical Optical Instrument. Cambridge University Press. ISBN 9781107493599.
  2. 1 2 A NEW TYPE OF TELESCOPE (PDF). Whitesville NY News. 1906.
  3. ↑ the elementary theory of the symmetrical optical instrument. CUP Archive. pp. 38–. GGKEY:DXCWGNP8PB1.
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