“Strangers in the Night..”
Posted by reedcat | Posted in Articles, Uncategorized | Posted on 17-09-2007
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As you probably know, the exposure meter collects data from many points on an image. The microcontroller processes this array, looks for the darkest and lightest points and places optimal, in its opinion, exposure somewhere near the middle point. The problem is night shots differ with dominant segments of low luminance, but your camera doesn’t know it. The logic of the processing program is oriented to look for optimal balance for showing both dark and light places and this task has its highest priority.
To correct this you should to use an exposure correction to inform the camera about the unusual conditions. Correction is measured in special units: “eV” or “exposure values”. This is not an absolute, but a relative value. Changing it by 1 eV means changing the light quantity by one aperture or shutter speed grade, or 2 times as mentioned earlier. Positive correction values are used for shooting of very light subjects, and negative for dark ones.

For the described conditions you should set an exposure correction in the range -1…-2. To study which value should be set you can experiment. Try to take shots with different values and after some practise you will be able to set it up easily.
Next way: try to set “spot” metering. But be carefully by selecting a zone for metering: it must be not darkest and not brightest point on a shot
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Next problem is almost hopeless with point-and-shot cameras. With long exposure (above approx. 1 s) and especially with high ISO values (depending on your camera it may be ISO 400 or ISO 1600) on dark areas will be visible a noice. It looks like coloured pixels (see photo below. Sometimes this noice may be reduced with photo processing. This is a price for low-cost CMOS sensors. Try to set lowest ISO values manually. Yes, it calls longer exposure time, but with tripod it is not very critical.

To be continued…

