I manage a Time Machine backup for a photographer. We had a 2TB drive for photos and a 2TB drive for the Time Machine backup of those photos. The Time Machine backup drive has run out of space and we realized that it's time that we can remove photos from the main photo drive (and burn DVD backups) anyways. Since Time Machine keeps deleted files, simply deleting them from the main drive won't help us in freeing up the space on the Time Machine drive. What is the correct way to handle this problem?
Here is a Q&A covering manual ways of cleaning backups.
You can always just wait for Time Machine to delete old backups as there really is no need to free up space on the backup volume. In cases where you may need to recover old backups and don't have a proper archiving solution, some people archive the entire drive once it fills and start with a clean one.
As a photographer almost always has a separate archiving solution, letting Time Machine manage the backup space is often a workable plan and maintains a good 6 months of deleted data in all the cases I've seen on 2 TB drives.