This may be an obvious question, but I don't know, which is why I'm asking here. I've searched "Canberra canopy porthole" and "window", but didn't get any information. There is a porthole of sorts on the left side of the canopy of this bomber, I'm wondering what it's for.
Here is a view from inside the cockpit:
There also appears to be a similar thing on the bottom of the nose of the aircraft, offset to its right. The following is a screenshot from a video game, as I wasn't to find a photo of this.
I'm tempted to say that this second one is to do with bomb sighting, however if it weren't there, the bomber would have just as good a view, wouldn't they?