not sure what they're called, you attach a little video recorder to your camera so you get a little more of what the camera may be seeing. hard to explain so i'll link to a video :P
from the trailer of War Photographer (beautiful film btw, everyone should see it)
YouTube - War Photographer - James Nachtwey @ 1:18 you can see the video recorder in use
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these videos give me confidence i can use Pentax professionally hehe
official name of the product would help so i can search for prices :P