Why do we use manual exposure mode?
We use manual exposure mode (“M” on the dial on top) when it is more convenient to do so than to use an automatic or semi-automatic mode – i.e. when the drawbacks are outweighed by the advantages.
Automatic modes (camera sets both aperture and shutter) and semi-automatic modes (camera sets one after you set the other) are convenient and quick, but are also error-prone. In particular, they do not handle the following well:
- Dark or light subjects
- Varying subjects
- Varying light across a scene
In those situations it is often better to use manual, assuming you have a moment to work out the best setting – and then to stick to these settings. So “indoors” is often like that, as is “night scenes”. As you get more experienced, you will use manual more often.
(One more note for beginners” manual exposure mode is not the same as manual focus, or manual focus spot selection, or manual white balance setting – etc. Unrelated!)