I have a Canon EOS 80D camera. I recently purchased a Canon EF 16-35mm f/4L IS USM lens which I plan to use on my next holiday later this year. I will be going on a cruise ship and was wondering if anyone could give me a rough guide on aperture, ISO and shutter speed settings. For example, if I am taking an indoor photo of a subject and I want the background in focus too. I have used Manual settings for years. I find outdoor photos ok given that I can work around lighting levels, however sometimes it can be more difficult with indoor settings on something like a cruise ship where lighting levels can vary in different locations. I don't want to raise the ISO too much in case of grainy images. Is it ok to use the camera's inbuilt flash?