If you are talking about the old cameras I would say that perhaps you meant the '"bellows unit'' the folding bellows used to focus the image, if I am not mistaken.
I don´t know what you meant with beamline, but perhaps you refer to the front or rears movement of the standards.
If you are talking about more contemporary cameras, you might talking about bag bellows (an optional expandable accessory).
To my thinking the obturator has to do with the shutter speed (the exposure time) and the bellows is the (generally, in the cameras of old, corrugated) container which separates the lens and the film. https://en.wikipedia.org/wiki/Shutter_speed
I have found it described as "a caixa de vista do fole do obturador'", which now makes more sense.https://en.wiktionary.org/wiki/bellowshttps://en.wikipedia.org/wiki/View_camerahttps://en.wikipedia.org/wiki/Bellows_(photography