effects on focus and background of flash vs natural light

These two photos are taken seconds apart, but are perfect examples of the problems regularly faced when trying to take photographs at places with insufficient lighting.



This first photo uses the flash to get the subject in the foreground properly exposed. However, please note that the area in the background is much darker (we won't discuss the quality of the light here).

This next example uses a much longer exposure with only natural light.

While the background is exposed more evenly, the subject is out of focus because the exposure was too long.

While in theory you can use the flash to expose the subject and then "drag" the shutter to expose the background, in an exposure this long, it is very difficult to keep the camera still. The easiest way to do this dragging technique is to shoot in Aperture priority mode, and then do and EV compensation of +1 to +2 while using the flash. Otherwise, you have to take the first picture with the flash, switch to manual and use the same Aperture and ISO settings but extend the shutter length and keeping the flash power the same (which may also require manual control of the flash).