I'm still new to photography and started with Canon EOS T2i. I rented Canon EOS 5D Mark II for a recent trip I made to Florida. This is the first time I used a FF camera and I can say that it blew my mind away with its image quality. I took 5D2, 24-105L and Canon 50mm f/1.4 with me. Most of the time this combo gave me stunning pictures however camera failed to expose correctly in low light conditions. I was using Aperture priority mode for more than 75% of the time with center focus point. ISO was in auto.
For example look at the following pictures, first one is f/1.4, 1/50s ISO 500 and second one is f/1.4, 1/50s ISO 2500. Both with center focus point and spot metering (tried with other metering options as well but results were same). First photo is little underexposed but second photo is over exposed. Can any please explain me why camera decide to choose two different ISO settings for shots taken in almost same environment. I still get confused with metering modes, if possible please explain that too.
f/1.4 1/50s and ISO500
f/1.4 1/50s and ISO2500
PS: I recently started shooting in RAW so I was able to fix the exposure and white balance on these photos.
PS 2: I'm sorry if I'm posting this thread in wrong section as I wasn't sure where to post it.