Westminster fountain at sunset

by Jorge Córdoba

submit your photo


Hall of Fame
View past winners from this year

Please participate in Meta
and help us grow.

Take the 2-minute tour ×
Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It's 100% free, no registration required.

I am reading a photography book which talk about dragging the shutter when a flash is used. It just tell me how to do this trick but doesn't explain why.

Can someone here tell me more about how it works?

I tried it at home and doesn't see the different. Maybe I am doing it wrong...

share|improve this question
    

1 Answer 1

up vote 5 down vote accepted

The idea is that you have two sources of illumination: the ambient light and the flash.

Becasue the flash is such a short duration, if you change your shutter speed from say 1/200th to 1/100th, it will not affect the amount of flash exposure since that is a constant amount of light that will occur in a fraction of those exposures.

However changing the shutter speed (keeping aperture constant) will affect the amount of ambient light. So as you lower the shutter speed, you will lighten the overall exposure, while anything that is mainly illuminated by the flash will remain relatively constant.

The second concept is that the flash will only illuminate things close to the flash, but will not affect the background, assuming the background is relatively far from the camera.

So when you put all this together, by changing the shutter speed you can affect your background (as if the flash wasn't there, since the flash won't affect your background) while your subject will have about the same exposure.

So then dragging the shutter is a way of having a well lit subject, mainly due to flash, but then being able to artistically adjust the background. If there is a sunset you might want to darken the background to give a more dramatic, saturated look for example.

If your experiments at home failed, this could be due to a few reasons. First, your subject needs to be relatively close compared to your background. Otherwise the flash will light up the background and the ambient light will be minimized and you won't see the effect. Also, as you change the shutter speed, you'll want to keep aperture fixed. So I'd use Manual mode, otherwise the camera will adjust aperture and the ambient exposure will remain constant, which isn't what you want if you are dragging the shutter.

share|improve this answer
    
Thanks but then if I slower the shutter speed, will it make the picture blur due to my hands may shake when I am taking a picture? –  Kintarō Jan 26 '13 at 0:58
    
If the shutter speed gets too slow, yes it may. But mainly the background would be blurred because the main subject will be lit primarily by the flash, which is very short duration. –  MikeW Jan 26 '13 at 4:45

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.