## Mashy 2 years ago Myophia correction doubt I understand what myophia is.. but my doubt is when it is corrected using a diverging lens.. all it does is that it brings the far objects to the far point for example.. if a person is myophic with 100cm as far point (meaning he cannot see clearly anything farther than 100cms).. then usng divernging lens we make sure any object at infinity is brought to 100 cm . what i don't understand is.. now the near objects will be even closer.. and might get closer than the near point of the eye (25cm).. does this mean when myophic person has to see somthing near by

1. Mashy

he has to remove his glasses?

2. Mashy

@yrelhan4

3. rajathsbhat

No. I'm myopic.

4. Mashy

5. rajathsbhat

My power is -1.00 And no, I don't have to remove glasses when I read a book (a rare event). People have this misconception about the near point of an eye. The near point is not the point before which you can't see clearly. I can see the tip of a pen-nib perfectly clearly (if I concentrate hard enough) even when it's about 3 cm from my nose. It's just the point before which there is considerable strain on your eye. But you are right in saying that the nearest point (i.e. 3 cm for me) shifts further away from you. For example, when i wear my glasses, my nearest point shifts to about 5 cm. P.S. That means that a myopic person strains his eye more than a person with normal vision while reading a book.

6. Mashy

Ok.. that makes sense.. so its WISE to remove glasses ? :P

7. Mashy

Your power is 1 D.. which means the focal length is 1m wow that means you are myophic with a far point of 100cm!.. ? :D

8. rajathsbhat

I guess...but text does seem clearer when I have my glasses on. I don't know if that's because my eyes are used to wearing glasses or not.

9. Mashy

anything farther than 100cm and you can't see.. :D

10. Mashy

hmmm damn.. i should have done more research before my lecture tomo :P.. but its ok.. lemme not get too detailed :D

11. rajathsbhat

That's not true. Anything farther than 100 cm is not clearly focussed on my retina and starts to appear blurry.

12. Mashy

yea yea.. thats what i meant.. can't see properly! ^_^

13. Mashy

i had one more doubt.. if you are hyperobic then you are wearing converging lenses so if you now look at far away objects.. (which would be outside the focal length).. they would start giving you INVERTED images right???

14. Mashy

so you would see blurry inverted images ?? i wish i had a reading glass somewhere near by!! :(

15. Mashy

@rajathsbhat

16. rajathsbhat

No. A reading lens effectively makes you myopic (think about it). When you try to see the head of a pin from far away using a reading glass it just appears blurry because it produces an image that is sort of a patch on the retina. |dw:1365533782928:dw| Since you can consider the pin as a collection of such points, each point on the pin produces a patch of an image on the retina and as a result, you see a blurry pin. I image of the pin is inverted. That's of course how every image is.

17. rajathsbhat

And remember that each of these patches is circular. That should clear up the upside down doubt.

18. Mashy

wait what?!?:O

19. rajathsbhat

what's wrong?

20. Mashy

m getting confused.. there are two ways i think of it.. one way is whether the light rays will get diverged or converged.. if i think that way.. its pretty simple to understand another way i think is quantitatively about where the image would be formed.. see if you are hypermetropic, that means you have a near point.. lets say something like 75cm.. that means he can't see anything within 75cms right?.. so in the problem.. they wanted me to make him read a book about 25cms away.. so putting the equation i get the f = 35.5 cm.. thats fine.. but now what i think is if the object is kept at 50cm (more than the focal length).. it would create a REAL image what about it?!? cause in all the rectifications.. the lens are supposed to create VIRTUAL images which now acts as an object for our eyes!

21. Mashy

wait.. the real image that it would create would be way way far behind the retina?!

22. Mashy

or this is just crazy?!

23. Mashy

its 37.5 cm.. focal length for the earlier one..

24. rajathsbhat

you have several things mixed up. First of all, there's nothing wrong with a lens creating a real image. Your eyes can see virtual/real images (objects). For example, you can see yourself in a mirror (virtual image) AND you can see a computer screen (real object/image). That's what special about a converging lens. Second, I have no idea why you think the image would be formed "way way behind the retina". Our eyes have lenses of variable focal length. We are special. I hope that answers that question.

25. Mashy

no i meant the REAL image of the LENS would be formed way way behind.. and this REAL image will now start acting as a virtual object for our eyes|dw:1365535349110:dw| so that real image now starts acting as an object for my eyes and hence it would now make a real image at the retina.. (just like how you derive formula for 2 thin lenses in contact) but this image is inverted.. so the object for the eye is inverted.. unlike the (real object or the virtual images you are talking about)

26. Mashy

do you have a magnifying glass?!? if you do please hold it near the eye and see far away objects.. they should look inverted :(

27. Mashy

and in the drawing.. i haven't shown the refraction made by the eye lens!

28. Mashy

OH I GET IT!! so here also it produces an inverted image in the retina.. and for virtual images also it produces inverted images in the retina.. ok ok i get it.. !!

29. Mashy

i was thinking in terms of concave mirrors how concave mirrors produce real images and they appear inverted to us..? :D

30. Mashy

so if the inverted image is produced in BETWEEN the two lenses.. THEN .. then it will produce an upright image on teh retina.. and hence we wil the see it inverted right? :D

31. Mashy

correct na? :D

32. rajathsbhat

you will NOT see an inverted image when you look at far away objects through a reading lens. The only way that'll happen is if the reading lens/magnifying lens is so far away from you that the rays that come into your eye ARE ALREADY INVERTED. |dw:1365535994325:dw| the image is upright on the retine --->you'll *see* an inverted image.

33. Mashy

yea i got it :D.. i got it.. !! thank you so much...i think i love you :O

34. rajathsbhat

If the lens in question is a reading lens that you have close to your eye, you'll ALWAYS see and upright image. The convex lens is converging the rays and your eye lens is converging it even more.

35. rajathsbhat

lol you're welcome.

36. Mashy

no seriously.. that was a huge help.. now i understand it better ^_^!!

37. rajathsbhat

so, do you accept that far away objects appear upright and blurry when you see them through reading glasses? If so, mission accomplished.

38. Mashy

yes yes yes yes i agree i get it .. i totally perfectly get it.. thats why you were an extremely big help :) :) :) :)!!!!

39. rajathsbhat

Great!