General Question

Timebomb's avatar

How to turn dioptres into focal length?

Asked by Timebomb (240points) December 21st, 2009

I was under the impression to turn dioptres to the focal length I divide 1 by it. E.G. 3.3 dioptres equals ⅓.3=3.0303r.
I now is this also true with negative numbers E.G. -0.2 because it’s not working in my equations.

Observing members: 0 Composing members: 0

5 Answers

jahono's avatar

You’ve got it right. The dioptres = 1/focal length, so focal length = 1/dioptres.
e.g. 3.3 dioptres = 1/(3.3) = 0.30303m focal length
-2 dioptres = 1/(-2) = -0.5m focal length

http://medical-dictionary.thefreedictionary.com/Dioptres for more info.

Timebomb's avatar

@jahono
The book I’m working on says the answer should be 5.0m not -5m, meh.

jahono's avatar

Hmmm I call typo, or slackness with signs. It would be 5m but in the negative direction (on the side of the lens where the parrallel light rays are coming from) so yeah should be -5m (for a -1/5 dioptre lens).

SirGoofy's avatar

With the ALL NEW Diopter Conversion Kit FL9000….that’s right folks….with the incredible DCKFL9000 you can convert all your dioptres into focal length in just minutes!! Save time, and keep your customers satisfied! No more doodling with pencils or wracking your brain while you patient sits there getting more impatient! Order today and we’ll throw in a year’s supply of Optometrist’s EYEYELLOWExtra. A fun gag gift your patients will just LOVE—- they’ll be laughing for years!! (A temporary simulation of viewing the world through BEER GOOGLES without the effects of alcohol).

engineeristerminatorisWOLV's avatar

Dioptre=1/Focal length.
Let’s take an example.
A person can see things clearly upto a distance of 50 cms and not beyond that, what would be the power in D of the lenses he’d use and what would be the type of lens.If another person can’t see near objects clearly within a distance of 50 cms,what would be the type of lenses he’d be using to rectify his vision and what would be the power in dioptre?
.
Sounds interesting, but the lenses that are used for near vision and far vision are different.For short-sighted vision concave lenses are used and for distant vision(the name is confusing,but distance vision means ability to see distant objects better and have a hazy near vision.This is seen in middle age people generally who have problem reading books,but can see distant things clearly) convex lenses are used.In case of difficulty to see distant objects,the power of the lenses are in + and in shortsightedness it’s -.
The reson for this is, in short vision,the image is formed before the retina and in distant vision it’s formed behind the retina.Anything behind the retina is termed as plus and infront of the retina is minus.
.
So the modified formulas for short-sightedness is D=-1/f and for Hypermetropia or longsightedness D=1/f
In the above examples,f=50 cm
So here 1 f is taken in meters
So for teh first part of the question it’d be -1/0.5= -2D and concave lens and for the second part it’s 1/0.5= 2D and convex lens.
Thank you all
ETW.

Answer this question

Login

or

Join

to answer.

This question is in the General Section. Responses must be helpful and on-topic.

Your answer will be saved while you login or join.

Have a question? Ask Fluther!

What do you know more about?
or
Knowledge Networking @ Fluther