recognising lenses and basic marking ( tutorial 1 )

Question 1

how to know if a lens is positive?

Answer 1

1. at least one convex curve
2. magnifies object
3. against movement

Question 2

how to know if a lens is negative?

Answer 2

1. at least one concave curve
2. minifies object
3. with movement

Question 3

how to estimate power of lens?

Answer 3

1. thickness- the thicker the lens the higher the lens power
2. weight - the heavier the lens the higher the lens power
3. speed of movement - the slower the speed of movement the higher the lens power and faster movement the lower lens power.

Question 4

what powers can a spherical lens be?

Answer 4

negative
positive
plano

Question 5

what happens in a plano lens?

Answer 5

when looking at vertical or horizontal lines in the lens and you move it to the right the cross within the lens will stay where it is and no movement of image
-no movement of cross image

Question 6

what is the centre of intersection of positive and negative lens ?

Answer 6

optical lens

Question 7

what happens when you move a positive lens to the right?

Answer 7

.the image of the cross within the lens moves to the left

.moves in opposite direction to where you move the lens

Question 8

how to neutralise a positive lens?

Answer 8

use a minus lens of equal power to neutralise a positive lens

Question 9

what happens when you move a negative lens to the right?

Answer 9

. the image of the cross within the lens moves to the right

. moves in the same direction to where you move the lens

Question 10

how to neutralise a negative lens?

Answer 10

use a positive lens of equal power to neutralise a negative lens

Question 11

what is optical centre of a lens?

Answer 11

. vision is best at this point

. limited optical aberration

Question 12

how can you describe the power of lens in a spherical lens?

Answer 12

the power of lens in a spherical lens is the same in all meridians

Question 13

how can you describe the power of lens in a cylindrical lens?

Answer 13

the power of lens is different in all meridians

Question 14

what to do if a lens contains a cylinder?

Answer 14

must mark optical centre and principal meridians

Question 15

How to find the meridians from using toric lenses?

Answer 15

• First you find where the limbs are at 90 degrees to one another and then mark them (as they are slanted due to being astigmatic) as meridians. (scissor movement)
• Then you move the glasses up and down and left and right to find where the lines intersect as that is where the optical axis is and you mark that down.

Question 16

How do we find the meridian of one via the cylindrical and topic lenses?

Answer 16

• We twist in the scissor movement
• We mark the lines (vertical or horizontal) that is going WITH movement
• Mark the vertical axis with a W

Question 17

How do you neutralise the W vertical meridian to find sphere?

Answer 17

• Neutralising across axis will give the sphere.
• observe up and down movement looking at the horizontal line and see what movement there is
• check the speed of movement

Question 18

How do you neutralise the other meridian to find cyl?

Answer 18

• keep the trial sphere lens
• add the cyl lens to n neutralise the other meridian
• then line up the cyl lens with the vertical line