Lookout lens
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A plastics wide-angle fresnel lens of the piano-concave type marketed by Eberhardt has a diameter of 11 in. and is designed for sticking on a flat glass surface to provide a panoramic view of the scene on the other side of the glass.
It is claimed that a conventional glass lens with comparable characteristics would be 4in. thick at the edges, weigh over 141b and have an excessive cost.
The lens is known as the Lensor Lookout; it is virtually weightless and has a focal length of 12in. It is made of pvc and is asphericized to eliminate spherical aberration. If necessary it can be cut to size with a pair of scissors. Applications could include attachment to the window of transport depot to obtain a better view of the yard. Price: £2.80.
Marketed by: Eberhardt and Co Ltd, Prospect Road, Portsmouth P01 4QY.