The lens mounting scheme in this design reflects the design intent of the system to be a fixed-focus, unitized sensor system with no anticipated need for change of focus, aperture, or field of view.  Because of this, a cassette approach was used in design, mounting, and assembly of the lens system.  The cassette method provides a simple assembly procedure that is yields relatively tight tolerances with relatively little assembly expertise required. It also lends itself to robotic production of lens systems, as predetermined fixtures can be used in the assembly of the lens system.  This design concept has been utilized in optical system design and assembly for decades and was pioneered by microscope manufacturers as a way of mass producing precision microscope objectives.

In this example, the lenses and aperture stop were grouped into five cells, lens 1 in the first cell, lenses 2 and 3 in the second cell, the aperture stop in the third cell, lenses 4 and 5 in the fourth cell, and lens 6 in the fifth cell.  Because the lenses all had relatively similar glass edge diameters and there was no need to radically lightweight the design, a single diameter lens tube was used to house the cells and attach the lens system to the sensor housing.  The lens tube is also relatively short in relation to its diameter so internal threading along the whole length poses no significant issues in this case.

Mounting the optics into their cells was accomplished by the use of an adhesive.  Proper application of the adhesive tends to force the lens to the center of the cell bore.  It is important to contact the manufacturer of the adhesive that you intend to use in your application to get the design notes on that particular adhesive.  The notes will provide useful information for the design and manufacturing processes, helping you avoid headaches later on.

The double lens cells are assembled in a particular order so that the lenses themselves can be used as fixturing platforms in the assembly process.  By installing the larger lenses first, the flat surface can be used to locate the smaller diameter lens.  In this design, holes were drilled radially in the double lens cell to allow the adhesive to be placed accurately in the annulus between the lens and the cell.

Once the lenses are mounted in their cells they can be measured interferometrically for quality assurance and to accurately measure the relationship between the lens and its cell.  This relationship will then be used in the assembly of the system.  These measurements can be added to the traveler document that accompanies the lens cell, so the assembly technician can put in the correct offset during the assembly of the rest of the system.  These measurements can be tracked electronically with the lens cell by the assembly machine if this system is to be assembled robotically.

The assembly is rather straight forward from this point.  To start, one end of the lens tube will be used as a datum and all the cells will be placed inside relative to this datum.  Decentration of the cells inside the lens tube was mitigated in this case due to the system being assembled vertically and thread lock compound being added to the cells after each insertion.  A note on thread locking compounds: there can be outgassing issues with some compounds so, again, it is important to contact the manufacturer for information on the compound that you intend to use.