If an object is on one side of the concave lens, the concave lens can form the image of the object. If the position of the object on one side of the concave lens is known, how to draw the image formation of the object? Suppose an object is on the left side of the concave lens, as shown in the figure below.
Orange line = the concave lens
Blue line = the principal axis
Arrow (green) = object
F1 = the focal length 1 and F2 = the focal length 2
The figure of the object’s image is obtained by drawing all the beams of light passing through the object, but this is less practical because there will be many lines representing light beams. For simplicity, just a few beams of light are chosen to represent all the beams of light passing through the object. Since this event involves refraction of light, the law of refraction of light must be obeyed when drawing the image formation.
Three beams of light or three rays
Ray 1 :
Ray 1 that comes to the concave lens is drawn parallel to the principal axis and touches the top edge of the object,
then refracted by the concave lens, where the beam of light refracts as if coming from the focal point. The incoming rays and the refractive rays that are must meet the law of refraction of light.
Ray 2 :
Ray 2 that comes towards the concave lens is drawn as if going to the focal point and touching the upper end of the object,
then refracted by the concave lens, where the refracted beam of light must parallel the principal axis. The incoming rays and the refractive rays that are draw must fulfill the law of refraction of light.
Ray 3 :
Ray 3 coming to the concave lens are drawn past the point of intersection of the concave lens and the principal axis.
Image formation (two rays)
The image formation can be drawn using only two rays, as shown below. If using two rays, there are three possible figures of the image formation.
Ray 1 and 2
Ray 1 and 3
Ray 2 and 3
Draw the images formation using only two rays need to be adjusted to the object distance from the concave lens. If the object distance from the concave lens is as in the figure above, there are three ways to draw the image formation using only two rays. If the object distance from the concave lens is different from the figure above,
for example, the object is between the focal point and the lens, then there is no need for three ways to draw the image formation, maybe there are only two ways to draw.
If you draw the image formation by the concave lens, you can choose one method and do not need to use two or three ways.
Image formation (three rays)
The image formation can be drawn using three rays, as shown in the figure below.
If the object distance from the concave lens is not as in the figure above, for example, the object is between the concave lens and the focal point,
or the object is between the focal point and the center of the curvature of the concave lens, then it is not necessarily the formation of image can be drawn using three ways like the figure above. There can only be two ways to draw the image formation.
Please observe the example image of the image formation by the concave lens, where the object distance from the concave lenses, varies, regarding the image formation by the concave lens.
