What does F-theta lens mean?

F-theta lenses are designed to focus a laser beam onto a planar image plane. They are often used in a scanning system with two galvanometer mirrors. One mirror is responsible for beam deflection in one direction and the second one for the perpendicular direction.

What does Theta mean in optics?

The angle of incidence is named with the Greek letter theta, and, since it is in medium 1, is called theta1. The refracted medium, water in this case, is called the second medium, or medium 2. The angle of refraction, again named with the Greek letter theta, is called theta2.

What is F-theta distortion?

F-theta lens distortion F-theta lenses (used in laser scanning systems) are usually designed to produce a certain amount of distortion (barrel distortion) so that the image height is proportional to the field angle of θ.

How does a scan lens work?

A significant feature of scanning lenses is the angle (φ) at which the focused beam strikes the work sur- face. In a typical lens, the beam will be normal to the surface only when the input beam is propagating along the lens axis. As the laser beam is deflecting off the axis, the angle moves off normal.

How does a telecentric lens work?

An image-space telecentric lens has the exit pupil at infinity and produces images of the same size regardless of the distance between the lens and the film or image sensor. This allows the lens to be focused to different distances without changing the size of the image.

What is tube lens?

A tube lens is placed within the body tube between the objective and the eyepieces to produce the intermediate image.

What is power of convex lens?

The power of a lens is defined as the reciprocal of the focal length. Converging (convex ) lenses have positive focal lengths, so they also have positive power values. Diverging (concave ) lenses have negative focal lengths, so they also have negative power values.

What is back focal length?

Back Focal Length – A mechanical measurement given as the distance between the last surface of an optical lens to its image plane.

What is Chiefray?

The chief ray is defined to be the ray from an off-axis point in the object passing through the center of the aperture stop; although there can be an infinite number of such rays, we can usually assume, at least for centered systems, that the chief ray is also restricted to the meridian plane.

What are F-Theta lenses and how do they work?

They are called f-theta lenses because the image height created by these lenses is linearly proportional to the focal length and the scanning angle theta. Difference in the focal plane for a convention lens, flat field scanning lens, and f-theta lens (image source Thor Labs)

How does the distance between F-Theta lens and scanner affect the scan field?

If the user increases the distance between f-theta lens and scanner the scan field will reduce because of the increasing beam height at the lens. Vignetting of the outer beams reduces the maximum scan field. Furthermore the telecentricity error may increase if the aperture stop distance changes.

How can I account for nonlinear displacement in F-Theta lenses?

While this nonlinear displacement can be accounted for with the proper software algorithm, the ideal solution is to produce a linear displacement (i.e., constant scan rate). F-theta lenses are designed with a barrel distortion that yields a displacement that is linear with θ (f*θ, see Fig. 1 C).

What is the difference between back focal length and back working distance?

It should be noted that the OSA is always zero for telecentric lenses. Back Focal Length (BFL) is the distance between the apex of the physical lens (outer glass element) to paraxial focus point. Back Working Distance (BWD) is simply the distance between the housing of the lens to the paraxial focus point.