Camera Obscura

I am going through the log book details of the late fighter pilot Hal Thomas. In his days tarining at No. 2 SFTS at RNZAF Station Woodbourne he flew Vickers Vincents (this is April-June 1940, before the days of the Harvards arriving).

Several entries for Vincent flights he has noted in the DUTY remarks column the words “Camera Obscura”.

I know what a camera obscura is, it is an instrument liek a periscope that through the optical lanses and mirrors projects the image onto a screen rather than looking through like a periscope or telescope, etc.

So, how did this apply onboard a bmber? Was the camera obscura used in a different way from how I describe? What was it used for? Bomb aiming?

I ahve never heard of one being used on an aircraft. Any ideas?