Fluid lens system includes a container enclosing a fluid arranged to refract incoming waves. A pressure release mechanism is in contact with the fluid so as to compensate changes in its volume due to thermal variations. The pressure release mechanism is positioned within a pathway of incoming waves. The fluid container may be connected via a tube to the fluid as a reservoir which is arranged within or outside the container, such as beyond an image sensor. Alternatively, an easily compressible body such as a small closed metal bellows enclosing a gas, is positioned inside the fluid to absorb volume changes by compression. The container may have an inner container part that fits inside an outer container part, where the pressure release mechanism is positioned within the outer container part. A fluid filled cavity including a compressible body may be formed between the inner and outer container parts.