Image Stability in Digital Photography

The third requirement we have to comply is avoiding that the picture comes out moved against our will. When a point moves perpendicular to a lens it's image also moves on the focal plane. If we move the lens, the image will displace correspondingly. If we are photographing in these conditions, the way the movement will be registered as a set of lines depends on the speed of the relative movement and exposure speed.

Objects in Movement
Any movements speed in absolute terms (km/hour, m/second) is isolated data that says very little. For us, what's important is the speed in regard with our field of vision or angular velocity , which also depends on the distance we are from the object in movement and the angle it's trajectory makes with our field of vision.

The closed you are to an object in movement, the greater it's angular velocity is in regard to us. With the same speed, an object crosses our field of vision, or camera's viewfinder faster the closer we are to it.

The angle it's trajectory makes with our field of vision also determines the greater or lesser angular speed regarding our field of vision or viewfinder. The maximum angular velocity of an object in movement happens when it's trajectory is perpendicular to our line of vision. When the object is getting closer or going away from us the only apparent movement is that of a diminishing or enlarging of the object's size. In this case, because of it's angular trajectory, angular speed is minimal.

When sharply capturing an image of an object in movement, we must remember that the faster it's going, the harder it's going to be, the closer it is to us and the closer it's trajectory is to perpendicular to our line of vision. The angular velocity of a child running close to the camera from left to right of the frame can be greater than that of a moving car that is far away and coming straight towards us. In a frame, the angular velocity also depends on the focal length of the lens we are using.