Manual lensemeter Flashcards
What is a lensmeter?
An instrument that determines the dioptric power, axis of cylinder, amount of prism, and position of the optical center of a lens.
What process forms the basis of all modern lensmeters?
Neutralization, where a known lens neutralizes the power of an unknown lens.
What are the primary functions of a lensmeter?
- Determine the dioptric power of a lens
- Determine the axis of cylinder of a lens
- Measure the amount of prism in a lens
- Identify the optical center position of a lens
What is the purpose of the reticle in a lensmeter?
To center a lens and determine the amount of prism within a lens.
How do you focus the eyepiece of a traditional lensmeter?
Rotate the eyepiece until the reticle is in focus, then adjust the power wheel.
What is the function of the auxiliary prisms in a lensmeter?
To shift the position of the target in relation to the reticle for accurate measurements.
True or False: The term ‘Lensometer’ is a generic term for all lensmeters.
False. ‘Lensometer’ is a brand name for a specific type of lensmeter.
Fill in the blank: A lensmeter with a circle of dots as the target is called the _______.
[European dot target or corona target]
What are the components of a traditional lensmeter?
- Cord and plug
- Power switch
- Power wheel
- Cylinder wheel
- Lens stop
- Lens table
- Lens holder
- Lens marking device
- Eyepiece
- Reticle alignment ring
What should be done to maintain a lensmeter?
- Clean the eyepiece lens
- Clean the lens-marking device
- Wash the ink pad
- Rewet the ink pad if dry
- Cover the lensmeter when not in use
How do you verify the accuracy of a lensmeter?
Use a biconvex test lens with its exact power etched, and compare the lensmeter reading to the lens’s vertex power.
What happens when using a lensmeter with greater than 6 diopters of prism?
Auxiliary prisms must be used to neutralize the excess prism for proper target visibility.
What is the typical reading for the reticle in a lensmeter?
Usually up to 6 diopters of prism.
What is the purpose of the lens marking device in a lensmeter?
To mark the optical center of the lens.
What type of target do most lensmeters use?
Cross-type target.
