I've tried different ISO settings as well as auto ISO, but whatever the ISO, when I'm in shutter priority mode, the camera isn't automatically adjusting the aperture as I change shutter speed. I'm just ending up with very dark pictures. Is this a problem with the camera or am I missing something? Help!
When the subject is too dark or too bright, it may not be possible to obtain the appropriate exposure. In such cases, the shutter speed indicator or aperture value indicator flashes when the shutter-release button is pressed halfway (except when the
Mmode is used). Change the shutter speed setting or aperture value [or ISO value].
Emphasis mine, words in brackets are condensed information from the rest of the original paragraph.
For better explanations, please see "What is the relationship between ISO, aperture, and shutter speed?"
There are three values that have influence on the exposure: ISO, shutter speed and aperture. You chose to set ISO and shutter speed, which leaves the aperture to the camera's CPU.
The aperture is limited by the lens's design - your camera has a variable maximum aperture of
f/3-5.9 (and a maximum ISO of 6400).
Think, for example, of the following situation:
The scene is very cloudy and therefore, you would need something like
ISO 400 @ 1/100s @ f/4. You, however, have decided to use
ISO 100 @ 1/200s - ISO alone would require 2 full stops, and the shorter shutter speed is 1 additional stop, so your aperture would need to be opened by 3 full stops, thus requiring
f/1.4 instead of
Your camera, however, can only deliver
f/3, resulting in a picture about 2 full stops too dark.
God - I hope that these calculations are correct. This always gives me a headache...