those images are there to point out 2 things-
1- the bridge shield generators are the huge bulbs on top of the bridge
2- the engines for a star destroyer are huge
I've got a picture, too.
http://www.theforce.net/swtc/Pix/kdy/blueisd1.gif
This blueprint was published in 1978, and clearly labels them as long-range scanners.
http://www.theforce.net/swtc/towers.html
The second link has an entire treatise on the subject, but it's about half-way down the page. Do a search on the page for "Sensor Globes." Whether you agree or not, it's a good read, with compelling arguments.
EDIT: Or just click on the "Sensor Globes" link at the top of the page
P.S.S. Also read the 2 sections following it. CINEFEX Proof has a quote from a special effects specialist on Return of the Jedi referring to them as radar domes, and the following section has some tidbits from the X-wing video games. Honestly, it's the X-wing video games that got me believing they are shield generators, but I never stopped to really think about it. It just doesn't make sense to me anymore.
Those are very good reasonings, and i don't think any one is arguing that they SHOULD be shield domes. But its ludicrous to take an outdated manual for an entirely different class of ship than the one we have 1st tier canon sources for, and some 2nd hand quotes from a special effects artist. Of course he's going to say they're radar domes. That's exactly what they look like in our world.
But its basic cause and effect in the movie: Dome goes boom, cutaway to bridge crew, officer yells about shields being lost. Thats 1st tier canon right there. There's no ambiguity. Otherwise i can argue that anytime you see Han shoot at a guy with his blaster and it cuts to his target getting hit, I can argue thats its some random guy offscreen shooting the poor stormy.
Edited by Bipolar Potter