I have been wanting to get a chance at getting a good photo of a loon for years. It took a few years because I had to find a loon that would stay around long enough for me to get a shot and to have a lens with the reach to get in close. I finally purchased a 600mm lens which allowed me to get in close to the loon without having to heavily crop in post. I used the cameras spot metering and metered off the loon to get a good exposure. I also wanted a fast shutter speed so I opened my aperture as much as possible.