Picture Style: I use Standard or Faithful but it is a subjective decision. It may be best to shoot Raw + Jpeg and in DPP you can use the Raw file to apply the different Picture Styles to see the one you might prefer.
Noise Reduction: I apply noise reduction as needed in post processing and normally do not use the in camera noise reduction but may be something you would want to experiment with. Experimentation is inexpensive in digital photography provided you have the time and desire to do it.
ISO: Depending on the camera shooting mode, I use an ISO that gives me the best combination of shutter speed, and aperture for the scene I want to photograph.
Again, it pays to experiment with the different camera modes, picture styles, apertures, and shutter speeds to see the combination that works best for you and the subjects you are trying to photograph.
Try shooting in P mode for a start and shoot the same subject and lighting to see how the ISO, Aperture, and Shutter speed effects the looks of your images. Do this by turning the Main while in P Mode to get different apertures and shutter speeds for a given ISO and then change the ISO to see the effect it has on aperture and shutter speed and on your images. This procedure may help you make informed decisions when the camera mode is in Av, Tv, or M modes.
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