Why 24mm and 70mm tell different stories, and when to open up.
Wide lenses (16–35mm) show space, exaggerate depth and suit movement. Long lenses (70mm+) flatten the background and flatter faces.
Your Sigma 24-70mm f/2.8 DG DN Art covers 24-70mm on full frame: wide for space and movement, long for faces and compression.
A face shot close with 24mm looks distorted (big nose); the same framing from further away at 70mm looks natural. Step back and zoom in for portraits.
Blue = what's in focus around the subject (●).
Wider aperture (smaller f-number) means a softer background and more light, but a thinner slice in focus. Longer lenses and closer subjects blur backgrounds even more.
Your lens opens to f/2.8. Use it wide open for low light and soft backgrounds, and stop down to f/4–5.6 for groups or moving subjects.