Near and Far Vision Flashcards
When you move the object closer to the lens
- image is further from lens
- magnified
How do you increase power in the eye?
accommodation via the crystalline lens
The near point of the eye
point nearest the eye at which an object can be placed and still have a sharp image produced on the retina
-normal eye is 25cm from eye, changes with age
What does the eye measure when looking at an object at a distance?
the angle, not the distance
How do you measure the visual angle?
= (image size h)/(distance d) h/d
what is the visual angle of the sun/moon as observed from Earth?
- 5 degrees
- the facet that this angle is almost the same for both is purely coincidence. The sun has 400 times the diameter, and is also 400 times away than the moon
visual angle
about how close things are in angles, not about how close they are. The further away, the smaller the angular spacing
A basketball player, 2M tall, 40m away subtends an angle=
0.05 rad
2/40=radians. to get degrees multiply by 360 and divide by 2pi
The bigger the visual angle…
the bigger the retinal image. cannot come closer than the near point
What does the near point produce?
the largest possible retinal image
magnifying lens principle of operation
object between lens and focal distance is virtual, upright, magnified
-image placed right at near point.
The object to be magnified with the magnifying lens is located
between the lens and its focal distance
the image observed via a magnified lens is located
at the near point of the eye
maximum lens magnifying power!!
= (25cm)/(f) + 1 ***
the magnifying lens
- what we observe with the naked eye through a magnifying lens is the image formed by a positive lens
- for comfortable observation, the object is located at the lens focal length
- for maximum magnification, the object is located at such a distance for its image to be formed at the near point
