Hey Cameron
There isn't a filter for Opportunity by Campaign. You can however customize the screen to add that yourself. You can take a look at the filters in place and use those as a guide to create yours. The actions for filtering are found on the Generate Report button. The field you'll want to filter for is “Campaign.”
You can also create your own report template or modify the existing ones. I'd start by going through the Report Designer tutorials first to get a grasp of the Report Designer. You also have the option of creating your own button and generating your own report if you desire.
Another completely different way to go about this would be to have a grid that lists your Opportunities like the one on the OpportuniesList screen (if you click on the little gear icon to the buttom right of the grid you have an option to add Campaign to the grid). You can then use the grid to filter for a Campaign. We then have a Export Grid to Excel action that you can use to get a spreadsheet of your Opportunities. This is a bit of a messier way to do it, but also perhaps a simpler way.
-- Mortaza