I've got the 20AM to wirelessly fire the 42AM on my NEX-6 (and it should be same on the 7). No it is not optical if what you're thinking of is the remote flash simply fires when it senses a flash pulse from the triggering flash. If that's the case then the built in popup flash on the NEX-7 could have been the commander and you won't have wireless TTL. If you read the link I sent the triggering flash actually sends a complex sequence of light signals to the remote flash, instructing to fire a metering burst, then tell the remote flash how much power to put out and then tell it to actually fire to illuminate the scene. That's why you need the 20AM because it can send out these complex instructions to the remote flash. Also, the light spillage is very small.