Magnifiers and Other Optical Devices
Telescopic Magnifying Devices
Using optical telescope principles a number of manufacturers have
produced spectacle mounted telescopic reading devices. Foremost
in this field would be the Keeler range of LVA telescopes that utilise
a unique mounting ring that attaches onto a spectacle lens. Once
attached it is possible to screw various telescopes onto the spectacles
for near vision and far vision use. The range of telescopic units
available includes wide area reading units, read-write units, short
focus distance units and rapid focus distance unit.
The advantages of these units are hands free operation,
reasonably good field of view, excellent optical performance and
ease of use. Like their simple magnifier counterparts there are
a few important points to remember when using these devices if they
are going to be beneficial. Firstly the working distance - all of
the near vision units within this category require a change in attitude
towards reading.
The distance from the spectacle mounted unit to the
reading matter needs to be quite short, typically 150mm or less
(depending on power/type) and as a result the user must learn to
hold print closer. Secondly the demands upon the muscles around
the eyes are increased with the extra concentration required when
using any high power device. Thus it is advisable to use the units
for short periods of time only and to have frequent rests whilst
using.
|
