The present disclosure is directed to automatic gain switching circuits for implementation with photodetectors that include a switchable storage network including a storage element. The switchable storage network, such as one or more capacitors, is configured and arranged to respond to a photocurrent from the photodetector and provide an increased storage for the circuit at a predetermined photocurrent. The storage elements can include one or more capacitors that can be coupled to integration capacitors of the photodetector. The switchable networks can include flux sensing switches such as MOSFETS that can activate at a desired or predetermined photocurrent level. Related methods of providing multiple gain values for a photodetector circuit, as well as focal plane arrays and imaging systems with automatic gain shifting are also described.