Recent questions tagged lenses

Description : How to know if contact lenses are expired?

Last Answer : answer:I'm tempted to say when you can't read the old prescription, but in all seriousness I think that's a question for your doctor. Different brands and types of lens, not to mention the ... of your eyesight as opposed to the last time you had it examined, would be the determining factors.

Description : What is the process of getting prescription lenses?

Last Answer : You need to get an appointment with an eye doctor and he or she will examine your eyes and write out a prescription for you. You can then take that prescription to a place that makes lenses and ask ... the lenses made at the doctor's office, but it seems to me that lenses are more expensive there.

Description : How do camera and human eye resemble with each other? What is the difference in their actions?

Last Answer : Similarities I. The retina of eye and film of camera serve the same purpose. II. Like camera, the eye lens forms a real and inverted image. III. Pupil of eye is similar to the aperture of ... In a camera lens can be moved back and forth the image on film but eye lens cannot move.

Description : Explain the defects in human eye.

Last Answer : I. Short-sightedness (Myopia) In short-sightedness a person can see near objects clearly but distant object appear blurred. Reason When the eye lens becomes much thicker or eyeball becomes too ... before they enter the eye. They are further bent by the eye lens to meet at the retina.

Description : Explain how eyes get used to darkness after sometime

Last Answer : When we suddenly move from bright light to dark area, the cone cells become de-activated but rod cell do not activated immediately so we can't see things clearly. But after some time rod cells becomes ... darkness I. Cone Cell: It activate in bright light II. Rod Cell: It activate in dim light

Description : What is a real and virtual image?

Last Answer : Real image The image that can be obtained on the screen is called real image. Virtual image The image that cannot be obtained on the screen is called virtual image.

Description : Define principal axis and optical axis.

Last Answer : The line passing through the optical centre and centre of curvature of the faces of the lens is called principal axis or optical axis.

Description : What is lens? Explain the difference between convex and concave lenses.

Last Answer : Lens: A lens is a piece of glass or other transparent material like plastic whose one or both side is spherical. Types There are two types of lenses. 1. Convex lens 2. Concave lens Convex lens ... thinner at the edges. Concave lens Concave lens is thinner in the middle and thicker at the edges.

Description : Define short-sightedness and long-sightedness.

Last Answer : In short-sightedness a person can see near objects clearly but distant object appear blurred. In long-sightedness a person can see distant objects clearly but near object appear blurred.

Description : How long our eye takes to acquire dark adoption at its maximum?

Last Answer : When we suddenly move from bright light to dark area, the cone cells become de-activated but rod cell do not activated immediately so we can't see things clearly. But after some time rod cells becomes ... darkness I. Cone Cell: It activate in bright light II. Rod Cell: It activate in dim light

Description : Can an image be obtained on the screen by a concave lens? Explain your answer briefly.

Last Answer : The ray diagram of concave lens for different positions of the object show that rays diverge out and do not meet on the other side of the lens after refraction. Therefore real image is not formed, but virtual image is formed on extending the rays backward.

Description : Upon what factor does the amount of light entering in a camera depend?

Last Answer : The size of aperture.

Description : How focal length is affected when the lens of eye becomes thicker?

Last Answer : In order to look something near to eye, ciliary muscles make the lens thicker and its focal length becomes shorter. So the image is formed on retina instead of point beyond it.

Description : Define focal length.

Last Answer : The distance between the optical centre (O) and focus point (F) of the lens is called focal length (f). Focal length of a convex lens is taken as positive.

Description : Write the name of instrument in which convex lens is used

Last Answer : II. Camera III. Binoculars IV. Magnifying glass V. Contact Lens

Description : How to Put in Contact Lenses

Last Answer : How to Put in Contact Lenses Glasses give you clear vision, but if you don't like the weight they put on your face or how you look while wearing them, one great alternative is to use contact ... on contact lenses correctly. Just follow these tips carefully and you'll have the 20/20 vision you need.

Description : How not to be mistaken when choosing contact lenses?

Last Answer : How not to be mistaken when choosing contact lenses? Contact lenses are currently the most common means of correcting vision. Now on the market there are a huge number of models of contact ... is better to choose products for sensitive eyes, which will avoid the occurrence of allergic reactions.