Prism question
To enduse prism on minus lens base up or down how do we move the lens?
example:
minus lens the base is at the bottom, therefore do we move the whole lens up to get base up prim?
I am not talking how does the lens look in the lensometer, i am talking about just the movement of the lens in reference to the lens table in the lensometer.
Can somebody please help me with that?
A plus lens the Base moves with where you move the lens. Aka if you move the lens up wile in the lensometer the Prism base will be base up. A Minus lens is the opposite. If you move the lens base up it will be a base down prism.
It depends where the eye is in relation to the OC. In a Plus lens if you move the lens up, so the eye is lower than the OC there is Base Up prism. In a Minus lens if you move the lens up, so the eye is lower than the OC there is Base Down prism.
Prism is always relative to the position of the eye as it relates to the OC.
Optical Cross: n. crucifixion apparatus used by the New Jersey State Board.
"It is not knowing, but the love of learning, that characterizes the scientific [person]." -Charles Sanders Peirce
"A concept is a brick. It can be used to build a courthouse of reason. Or it can be thrown through the window. -Gilles Deleuze
Plus Lens:
OC goes UP, BASE is UP
OC goes DOWN, BASE is DOWN
OC goes OUT, BASE is OUT
OC goes IN, BASE is IN
Minus Lens:
OC goes UP, BASE is DOWN
OC goes DOWN, BASE is UP
OC goes OUT, BASE is IN
OC goes IN, BASE is OUT
In short, know for a plus lens that the OC and base direction follow each other, and for a minus lens it's the opposite.
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