Most photographers rely almost exclusively on the automatic lightmeter in
their camera to produce an accurate exposure, and under most circumstances
this is not a problem. The through-the-lens (TTL) multi-segment evaluative
lightmeters found on most modern good quality cameras are very
sophisticated, and can cope with most situations quite adequately. However
even the best meter can be fooled by unusual lighting conditions or very
high contrast scenes into producing under- or over-exposed images.