It is a transparent refracting medium bounded by  two or at least one spherically curved surface in lens formula. 

What is lens using in various device :In a microscope or in a telescope convex lenses are used to see distant or much closer objects.

What is the type: Convex and Concave lens.

What is the definition:

Convex lens:  This type is thicker in the middle and thinner at the edges; in other words, it is a piece of a transparent medium that bulges out in the middle.

Concave lens: The shape of this type is just opposite to that of a convex type. It is thinner in the middle and thicker at the edges; in other words, it is a piece of a transparent medium bent inwards in the middle.

What is the structure  formed:  A convex type or concave type is the combination of frustum of prisms. We know that when a light ray falls on a prism it always bends towards the base of prism. The base of these prisms in a convex lens is towards principal axis of this type. Similarly in a concave lens base of the frustum of prism is away from the principal axis .

What is the activity on light on convex type:  If any parallel light ray falls on the convex type, when it strikes on any frustum of the prism it bends towards the base of this prism .Consequently all parallel light ray falling on one or the other such prisms bend towards their bases.  Since all bases are facing towards the principal axis the rays also converge towards the principal axis at a point which is known as real focus . 

What is the another name : For this property this type is also known as a converging lens. 

What is the activity on light on concave type:  If any parallel light ray falls on this  structure, when it strikes on any frustum of the prism it bends towards the base of this prism. Consequently all parallel light rays falling on one or the other such prisms bend towards their bases. Since all bases are facing away from the principal axis the rays appear to be coming from the point which is known as virtual focus . 

What is another name: For this reason this type is also known as a diverging lens.

What is the application :i) Eye lens is a convex type that forms the real and inverted image of any object on the retina.

ii) The eyepiece used in a camera, microscope and telescope are convex  

iii) A magnifying glass is a convex  used to  watch minute objects. 

iv) Spectacles are convex or concave to correct the vision of our eyes.

v) A concave  is used in a Gallilean telescope.

What is power: Power of a lens is defined in terms of the deviation produced by the this structure. 

We know, that a lens of smaller focal length deviates the light rays more than that  of higher focal length. More is  deviation of light higher is the power . Numerically the power  is equal to reciprocal of focal length  in meter. Power (P) = 1/ focal length in meter 

The unit of power is dioptre (D) .Convex type has positive (+) power and concave type has negative (-) power. When two or more thin structures are put in contact the power of the combination is equal to algebraic sum of powers of the lenses. If P1, P2, P3………..are the powers of the thin structureis equal to  the power of combination of lenses ,P = P1 + P2 + P3 +……… 

What is a macro lens : It  is a dedicated camera  lens that is optically optimized to handle extremely  close focusing distances and can take sharp, highly  detailed images of microscopic subjects. Macro lens is mainly used in photography. (what is a macro lens)

what is a macro type best example: 

  •  1 -Canon EF 100mm f/2 .8L Macro IS STM
  •  2 -Canon EF-S 35mm f/2.8 Macro IS STM
  •  3 -Tamron  SP 90mm f/2.8 Di VC USD Macro.
  •  4-Nikon AF-s 105mm f/2.8 G IF ED VR Micro.

What is a macro  focal length :There are many different  macro types on the market today, with focal lengths from 15mm to 200mm. most of the macro hit the same 1:1 magnification ratio that gives shooters the life sized reproduction they want for superb close-ups.

What is a macro type detection: If this structure  with a magnification ratio of 1:1 or 2:1 or 3:1 then it is a macro .  If the magnification ratio is 1:2, 1:3, 1:4 etc then it is not macro. 

What is a macro lens advantage:  This macro lens is good for shooting. Macro lens is used for close up. Macro lens is also used in close up photography.  A macro lens is a special type of camera lens that has the ability to work with very short focusing distance.  Macro lens is useful in taking sharp image of very small object.  What is a Macro type focusing distance : It is around 30 cm. 

What is the disadvantage: Sometimes macro lens can degrade the quality of the image. 

What is a macro \type termed so :Actually macro lens provides a large view of a small object. In other words,  macro lens makes the micro image MACRO.

What are toric lenses :A toric type  is a type  having different optical power and focal length in two orientations perpendicular to each other. One of the surfaces is shaped like a cap from a torus and  other one is usually spherical. Such toric type behaves like a combination of spherical and  cylindrical lens 

What are Toric lenses functions :A toric type is a contact lens that is shaped in a particular way.  The shape of toric type creates different refractive , or focusing, powers on the vertical and horizontal orientations.  If the object is moved around the toric type the refractive strength increases or decreases gradually.

What are  constituent of toric:  The toric  is made of some bio-compatible lens material. Toric IOL   technology uses bio-compatible material  have been successfully used in contact lens.

What are toric  problem of  becomeing blurry:  Toric is used in making contact lens.  If it is used for long time   then eyes may become blurred because of much dryness of inside our eye and the weighed lens  can’t swivel to be the right way up again by each blinking 

What are toric  comfortibility: Toric  is of  different types   with soft lenses which are the most popular among every one.  Users feel most comfortable using these toric  because of the hydrogel component,  which provides safety and  comfort. 

 What are  uses of toric: Toric type with different optical power and focal length are primarily used in  eye glasses , contact lense and intraocular lenses to correct astigmatism. 

Toric IOL reduce lifetime economic costs by reducing the need for glasses or contact lenses following cataract removal.   This results can inform  physicians and patients regarding the value of toric IOL in the treatment of  cataract  and pre-existing astigmatism 

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