Tutorial: Mounting Optical Lens Mir Salek Optomechanics, Fall 2008 1- introduction

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Tutorial: Mounting Optical Lens

Mir Salek

Optomechanics, Fall 2008

1- Introduction
An assembly of lens is hold usually in a lens barrel. Each lens is fixed in this barrel by a mounting structure. An example of a lens barrel is shown in Figure 1. The following criteria should be met by a lens mount:

1– It should define the position of the lenses to the required accuracy.

2– Does not deform or change the optical properties of the optics by stress

3 – Provides the required adjustments for the optics

4 – Protects the optics from the maximum predicted shock to the device

5 – Protect the optics in presence of environmental extremes such as extreme cold and heat or moisture. The device might not be operational in these extreme situations.

6 – Maintain its function upon operational environmental variations. The most common environment effects are temperature and vibrations.

Figure 1: a lens barrel assembly1

The position of the optics is defined by a fixed mechanical structure and a retainer pushes the optics to this reference point. Figure 2: Lens hold in the cell illustrates a lens hold in a cell. In this article, different methods of mounting the lens are presented. In each case, thermal properties and resistance to shock and vibration of the mount is discussed.

Figure 2: Lens hold in the cell2

2- Mounting the Lens
2-1- Mounting with Reference to the Mechanical Axis

In loose tolerance or less expensive systems, the position of the lens may be defined by its mechanical axis. Mechanical axis is defined by the mechanical edges of the lens. The major issue here is of course misalignment of optical axis of the lenses in the system. The other problem occurs when the lens has appreciable edge thickness. In this case, lenses might tip and their edges might crack. To avoid the latter problem either the edge of the lens is made in a circular format or a relief should be made in the cell. The former case is shown in Figure 3 and the latter case in Figure 4.

Figure 3: Details view of a lens with spherical rim3

Figure 4: Putting a relief in the cell to avoid jamming4

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