low vision aids

Question 1

what is a simple magnifier used for

Answer 1

simple magnifier are used for near vision only. - they are plus lenses

hand held , stand mounted spectacle mounted

light leaving has zero vergence

therefore patient will be wearing distance glasses

young person won’t accommodate - light leaving has 0 vergence

Question 2

what is the first focal point

Answer 2

where light leaves with 0 vergence - distance from lens a first focal length away

Question 3

a simple magnifier has a first focal length of 6.7cm how much magnification does it get a nominal setting (10cm)

Answer 3

step 1 - f lens = 1 / -f

+10d

magnification = +/4

+10/4 = 2.5

f = 6.7 cm

f lens = 1 / -(-0.067) = +15d

mag = 15/4 = +3.75

distances will have - signs in front of them

Question 4

what are telescopes made from

Answer 4

telescopes - we need 2 lenses to form telescopes

astro= 2 + lenses

galilean = a + and a - lense

this means that a telescope won’t change the vergence

light entering and leaving will have 0 vergence

telescopes can be used for near but they are usually used for distance

2 lenses - one that is weaker and one that is stronger

objective is always the weaker + Lense

eye piece is always the stronger of the lenses