When we view an object with naked eyes,the object must be placed somewhere between ininity and the near point.The maximum angled is subtended on the eye when the object is placed at the near point.This angle is
where h is the size of the object and D is the least distance for clear vision and
is the angle subtended on the naked eye when the object is placed at the near point.
This angle can be further increase if the converging lens of short focal length is placed just infront of the eye.When cnverging lens is usedfor this purpose,itis called a simple microscope or a magnifier.
Suppose,the lens has a focal length f which is less than D and let us move the object to the first focal point F.The eye receives rays which seems tocome from infinity.The actual size of the image is infinite but the angle subtended on lens is
, where f<D and thus
is the angle subended by the image on the eye when the microscope is used.
In this way one can view an image formed at infinity by a microscope.