Your second photo is definitely underexposed, but it's hard to know why. Lots of good suggestions so far. As to the first one, shooting in aperture priority is just fine, but it seems to me that your camera was focusing on the whole area. You might try using just one single focusing point, and put that on the subject, like the swan, to isolate it. At f5.6 at that distance, if you used an area focus mode, it's likely why the swan is not in sharp focus. Just a thought.
5.6/250 at 140mm on a dreary day ? Depending if it was spot, matrix, or centered and what the meter read to where it was pointed at what light source or portion there of? I see no issue why 3600 ISO ...
5.6/250 at ISO 100 with a 50 "might" be exposed although if dark and darker, 125 is imaginable.
And at 5.6 at 140 you will be able to separate as well, read the DOF table? Not foreground but subtle enough background
Landscapes should be shot full manual anyway - what a waste of good electronics
If your ISO changed "on its own," I can't help but think you have the auto ISO set. Together with that, I suspect that your point of focus (and with it, the spot from which your camera took its meter reading) may have shifted slightly from image to image. If, for example, you took your reading from the swan, it would be properly exposed and the background would be considerably darker. If you read from the background, the reverse would happen. This could be the case especially if your camera is set to spot metering, rather than "averaging."
If your ISO changed "on its own," I can'... (
Spot metering is a good tool, but one has to be careful when using it. Takes some precision to get thing right.
Dione, I spotted the problem right away..., you’re not using a Canon!!!
Dione, just kidding, your camera is fine, just your photography isn’t!!!
Dione, WELCOME to the Hog!!!
Well that was really helpful to OP. I hope you are proud of yourself.
Hey Dione, keep shooting!! I have grey hair and started with film. It cost money every time you clicked the camera! No so digital. Really, think of something to try just get out the camera and try!
BTW I did shoot a lot of landscape/nature. I would guess 90% of the time I shot in aperture priority. I also set the ISO. This means that the only exposure that is changed by the camera’s “strange electronic” is the shutter speed. Don’t know if it is any better to shoot this way, it is just a quirk of mine and if you are experimenting you only have one variable that you don’t control.