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Different relationships with the distance of the eye to the monitor screen:
One basic rule when testing a camera system is that the best optical correction is achieved!
When testing a compact system (where the XY reading table is part of the basic system and with the monitor screen above the camera) there are a number of important factors to be taken into consideration:
Here are a few important tips:
- Observe the direction of sight! The eyes should be at the level of the upper edge of the screen and look approx. 20 degrees downwards. With eccentric fixation, however, it can be correct to look downwards to the lower edge of the screen and take advantage of peripheral vision obliquely upwards! The important factor is that the axis of the direction of sight is downwardly directed!
- Normal “close distance” is 30 cm between the eyes and the screen. The camera in the compact system, however, looks at the lower edge for what is to be read and to come to the upper left hand corner where reading begins, the XY table must be fully extended. This often results in users having to move their bodies backwards the same amount - "you are pushed out by the reading table”. This movement has major consequences.
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THE DEPENDENCY OF MAGNIFICATION AND LUMINANCE ON DISTANCE
(Source: Lund/Watson CCTV-book -97)
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When the eye moves closer to the screen magnification on the retina increases.
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The effect of light/brightness on acuteness of vision.
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Light strength weakens 4-fold if the distance between the eye and the screen is doubled.
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Magnification:
If the eye moves from 30 cm to 60 cm, magnification on the retina is halved and vice versa, if the eye moves closer to the screen magnification on the retina increases. This is known as effective magnification and from the user’s point of view, is the most important. Lineal magnification – where the magnification of a letter or an object on the screen is measured – is a technical measurement and used for comparison only.
Light/brightness:
With the same movement from 30 to 60 cm the light/brightness is reduced 4-fold! It is a well known fact that the ageing eye requires stronger lighting! In addition, light is of major importance for certain diagnoses and not least of all, light is a determining factor for acuteness of vision!
Radiation:
Is no longer considered to be a problem as newer monitor screens satisfy TCO standards. TFT and LCD screens, which have become the most popular screens now, do not generate radiation!
CONCLUSION:
Try to maintains a constant distance between the eye and the screen!
Difficulties that occur with incorrect direction of sight:
It has been recognised that sight directed upwards, results in a “gritty” sensation and other discomforts in the eye. More recently, experience and research, reported by the Swedish National Board of Health and Welfare has shown that what is called astenopic difficulty (tired eyes) can be avoided by a downward direction of sight! (20-30 degrees)
What is less widely known is that with near-sightedness, the collaboration between three important functions of the eye, the Near-sight triad, deteriorates. This means that:
- Accommodation
- Convergence, and
- Pupil constriction
functions considerably worse when the sight is directed upwards! The triad functions best when sight is directed approx. 20 degrees downwards!
(Source: The National Board of Health and Welfare, http://www.socialstyrelsen.se/)
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Click respective product names for information
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IDEA-SCX
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SynSupport Sverige AB
Illervägen 15
SE-352 45 Växjö
Tel. +46 470-72 98 88
Fax. +46 470-74 95 80
E-mail. info@synsupport.com
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SONY partner
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