Canon patent application: New type of lens element bonding

There is a lot of things that go into building a lens that you never will see, but cause the designers no end in worry and effort.

An example is this patent, one in which we'll never know if it gets implemented, but is a problem that Canon wants to resolve.

The problem specified here is that when two elements are bonded together, they may deform, and change their optical characteristics depending on temperature, also over time the elements may peel, or crack the along the joint. So they use a flexible adhesive, but then during thermal expansion, the shape of the element may occur, and change the optical properties, so that's not perfect either.  In this patent application, the adhesive allows for the thermal contraction/expansion to occur without changing the overall shape of the element.

As Canon states;

If the optical element using a significantly different optical element linear expansion coefficient, even align the linear expansion coefficient of the optical elements sandwiching as specified in Patent Document 2, deformation of the optical element, the optical Peeling easily occurs at the interface between elements.

In order to solve the peeling at this interface, for example, after molding a thermosetting or photo-curing resin material into an optical element, it is known that the adhesive layer formed with an adhesive is bonded to the other optical element to suppress deformation. It has been. The adhesive layer whose elastic modulus is greatly lowered when the temperature is increased can satisfactorily prevent peeling at the interface between two different optical elements. However, an optical element using such an adhesive layer may have a large change in surface shape when the temperature is raised and then returned to the original temperature, which may reduce optical performance. 

Japan Patent Application 2019-133138