LORRAINE

Question 1

WHAT IS TRANSVERSE CHROMATIC ABERRATION MAINLY INFLUENCED BY?

Answer 1

abbe number

Question 2

WHERE DO ABERRATIONS INCREASE?

Answer 2

away from optical centre

Question 3

BEST FORM LENSES

Answer 3

minimises aberrations

tend to have steeper curves

Question 4

ADVANTAGE OF ASPHERIC LENS

Answer 4

flatter, thinner curve

Question 5

WHAT HAPPENS TO PLUS RX AS YOU MOVE FURTHER AWAY FROM EYE?

Answer 5

plus rx gets stronger moving away so lens needs to be weaker

Question 6

HYPEROCULARS

Answer 6

conventional solid, plastic high plus lenticulars

dispensed by magnification rather than power

Question 7

DIFFRACTIVE LENSES

Answer 7

rings get closer away from OC

surface angle increases

constant number of wavelengths

Question 8

FRESNEL LENSES

Answer 8

ring spacing usually constant

surface angle increases

usually thin, side, black, nylon frame

main use was temporary aphakic spectacles

Question 9

FROSTED LENSES

Answer 9

surface ground so that translucent but can’t see any object form

easy to make for plastic lenses

scouring powder or fine wet + dry paper

Question 10

CHAVASSE

Answer 10

hammered glass appearance

difficult to source

Question 11

HOW DOES A MINUS LENS CHANGE WHEN BVD INCREASES?

Answer 11

a minus lens becomes weaker

compensates for the change using a stronger lens