Okay, by HUD, I meant the HUD Glass. The thing that the gunsight is projected on. I felt it was more easily understood by everyone as a HUD, but if you want to give me the correct nomenclature, I will use it.
I was thinking that rather than a projection onto the glass, maybe the glass had reticle lines drawn on it, maybe a circle to show you the general area covered by the cameras if you went into a shallow dive. Perhaps they didn't dive, perhaps they kept to the standard level flight at between 8,000 and 10,000 ft that the F9F-5P operated at . Or maybe the 15,000 ft that the F2H-2P operated at.
I can see that if you have the target ahead of you and you know your distance to the target, you can calculate when to start recording at your given height. If you fly either the Banshee or the Panther Photo Recon aircraft, you could work out from their results at what point the target is passing into the camera field of view, and when it reaches the Nadir.
I'd love to know which Meteor book. The only one I have is "Meteor from the Cockpit" by Peter Caygill and all I remember is that it was a dangerous aircraft to land because the gears came down separately, not simultaneously, so using the airbrake was a no-no. In SF2 the Meteor is a MiG-killer, but according to the book the real one had a lot of problems.
Anyway, I'd better read it again.