Actually, I recently watched 'The Making of West Side Story-The Album), and it showed a lot of orchestral recording.
In fact, most albums are recorded in studios unless it's a live recording or if for some reason the orchestra is trying to get a certain sound for a piece (like in a church, etc)
Anyhow, if you are seeing a live event being recorded, there will be mics in the front on either side of the conductor, or mics will be placed throughout the orchestra sections.
In the West Side Story film, mics were placed in various sections, with close mics on instruments like the piano and guitar. Then, after the recording they are able to adjust the sounds by section. But, for the most part, orchestral works are recorded in the studio, not in the concert halls.
micro