OK I was reading in PRINCIPLES OF OPHTHALMIC LENSES something about converting diopters to degrees. How is this done and what is the relationship between the two? I am a little confused.
OK I was reading in PRINCIPLES OF OPHTHALMIC LENSES something about converting diopters to degrees. How is this done and what is the relationship between the two? I am a little confused.
Only done in prism deviation. One diopter deviates a point of light 1mm at a distance of one mm. One degree (almost never used in eyewear, and when it is the precriber or optician usually doesn't know the difference or correct terminology) deviates light one degree on the 180 degree protractor scale. This is usually only used in telescopes, astronomical calculations and long distance constructions. Then one may actually have degrees, minites and seconds.
Chip:cheers:
I always thought it was 1cm at 1m.Originally Posted by chip anderson
Specs, I think you are right. Somewhere around here I have a book that describes the difference and how to calculate the variation from diopters to degrees.
Chip
A prism diopter can be defined mathematically as:
Prism = 100 * tan Angle
where Angle is the angle of deviation in degrees. Solving for the angle of deviation gives us:
Angle = arctan (Prism / 100)
So, for instance, 1 prism diopter is equal to:
Angle = arctan (1 / 100) = 0.57 degrees
And 1 degree is equal to:
Prism = 100 * tan 1 = 1.75 prism diopters
For relatively small angles, since the tangent of an angle is nearly equal to the angle itself in radians, you can these as a rule-of-thumb:
1 Prism Diopter for every 0.57 Degrees and 1 Degree for every 1.75 Prism Diopters
Darryl J. Meister, ABOM
Ah! Thanks guys!!:cheers:
that is correct. This is a useful measure, as you can multiply it up and explain it to a patient easily - 7 prism dioptres relates to the image moving 7 cm @ 1 M or 70 cm @ 10M, "Imagine a car headlight at 10M the light would be dispalces 70 cm - it would look like 2 cars etc...."Originally Posted by CME4SPECS
hey optidonn, what is the exact name of that book and who wrote and published it and where can i get my hands on one? Thanks
writen by Mo Jalie, ISBN: 0900099208Originally Posted by rolandclaur
It is an old but excelent book, and it still stretches me. Nowadays I wish it was updated to cover more modern lenses, but as the title says - its all about learning the PRINCIPLES
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