In iOS 8, the Camera app has a lot of the same functionality as in iOS 7. In iOS 8, you are able to manually control the exposure levels in the photo. This means you can easily adjust how light or dark the photo is.
To do so open up the Camera app. Then you are going to tap on the focus point. The focus point is the subject point of the picture. When tapping to focus, a yellow square appears around the subject. To adjust the exposure level, tap on the yellow sun and slide it up and down. Sliding the sun up will make the picture lighter, and sliding the sun down will make the picture darker.
This same technique will work while using a filter.