How to Compensate for Long Shutter Speeds When there is too Much Light

[Reyed Mia (Apprentice, DIU)]

How to Compensate for Long Shutter Speeds When there is too Much Light

I mentioned above that one of the effects of using longer exposure times (slow shutter speeds) is that more light will get into your camera. Unless you compensate for this in some way this will lead to over exposed shots.

Below I'll suggest three main methods for making this compensation (note – a forth method is simply to wait for the light to change (ie for it to get darker). This is why many shots that incorporate blur are taken at night or at dawn/dusk):

1. Small Apertures

So how do you cut down the amount of light that gets into your camera to help compensate for a longer shutter speed? How about changing the size of the hole that the light comes in through. This is called adjusting your camera's Aperture.

If you shoot in shutter priority mode the camera will do this automatically for you – but if you're in manual mode you'll need to decrease your Aperture in a proportional amount to the amount that you lengthen the shutter speed.

Luckily this isn't as hard as you might think because shutter speed and aperture settings are organized in 'stops'. As you decrease shutter speed by a 'stop' you double the amount of time the shutter is open (eg – from 1/250 to 1/125). The same is true with Aperture settings – as you decrease the Aperture by one stop you decrease the size of the shutter opening by 50%. This is great because an adjustment of 1 stop in one means that you just need to adjust the other by 1 stop too and you'll still get good exposure.

2. Decrease Your ISO

Another way to compensate for the extra light that a longer shutter speed lets into your camera is to adjust the ISO setting of your camera. ISO impacts the sensitivity of your digital camera's image sensor. A higher number will make it more sensitive to light and a lower number will make the sensor less sensitive. Choose a low number and you'll find yourself able to choose longer shutter speeds.

3. Try a Neutral Density Filter

These filters cut down the light passing through your lens and into your camera which in turn allows you to use a slower shutter speed.

It is sort of like putting sunglasses on your camera (in fact some people actually have been known to use sunglasses when they didn't have an ND filter handy).

For instance, if you're shooting a landscape in a brightly lit situation but want a shutter speed of a second or more you could well end up with a very over exposed image. A ND filter can be very helpful in slowing the shutter speed down enough to still get a well balanced shot.

It is the use of ND filters that enabled some of the shots in our previous post to get a lot of motion blur while being taken in daylight.

Another type of filter that can have a similar impact is a polarizing filter. Keep in mind however that polarizers not only cut out some light but they can impact the look of your image in other ways (ie cut out reflection and even change the color of a sky – this may or may not be the look you're after).

Two More Technique to Try

Another technique to experiment if you're wanting to capture images with motion blur is to experiment with Slow Sync Flash. This combines longer shutter speeds with the use of a flash so that elements in the shot are frozen still while others are blurry. Read more about Slow Sync Flash. Another technique worth trying out is panning – moving your camera along with a moving subject so that they come out nicely in focus but the background blurs.

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