For a city not widely acclaimed as a major tourist destination, Oslo does offer a number of impressive sights. The modern Opera House is near the top of the list for me.
The building is huge and water surrounds it on three sides. When you are near it, there are not enough steps you can walk back to get a wide-angle shot. Practically all best shots of Oslo Opera House are taken from distance over water. For this full frontal view, you need to get out on Oslofjord. Taking pictures from a moving or gently rocking ship necessitates going for fast shutter speed in the shutter-priority mode. On a bright day, it will result in wide apertures and shorter depth of field than what you would normally want for wide-angle landscapes, but it thankfully matters little when your focus is effectively at infinity.
Walking up those roof ramps – especially in the morning when there are very few people around – is a free and easy way to get an elevated perspective over the city. Don’t miss it when you are in Oslo.