How slow should I set my shutter speed to capture motion blur?
Cars and trucks can play havoc with your compositions when shooting during the day. But at night city traffic is a real advantage.
The moving headlights and tail lights are converted into ribbons of red and white throughout your picture, making a surprisingly attractive feature of the rush-hour roads. But in order to create this effect you have to set a shutter speed that's slow enough.
The exact speed will depend on how fast the traffic is moving and on how much of the road you have in the frame. But, as a general rule, the longer the shutter speed the better.
This gives wider streaks and unbroken lines of light. For the average city street, an exposure of 20 seconds or more is ideal (but don't forget the tripod!). Factors such as traffic lights will mean you'll have to judge exactly when to start the exposure to maximise the movement during the shot.
How do I set a slow enough shutter speed?
An easy way to set the longest shutter speed available is to use your camera's Av mode. Then use the thumbwheel behind the shutter release button to set the narrowest aperture that your lens allows (usually between f/22 and f/32).
The maximum shutter speed available in this mode on many DSLRs is 30 seconds. To get longer shutter speeds, you need to switch to M (Manual mode).
Here you can use the Bulb setting to keep the shutter open for as long as the cable-release button is pressed (find out how to use Bulb mode). You may need an ND filter to reduce the amount of light reaching the sensor.
Which ISO setting should I use for night photography?
When setting an ISO value, a good rule to follow is to always use ISO100 unless you think you really need to change it.
Increasing the ISO will increase the sensitivity of your camera's sensor, so that you need less light to take a picture. You can set a different ISO value for every picture that you take.
But take care - your camera increases the sensor sensitivity by amplifying the electrical signal generated by the sensor, which makes for a noisier picture (find out how to reduce noise at high ISO settings). If you want top-quality pictures, keep the ISO as low as you can.
Just because you're shooting in low light, it doesn't mean that you should increase the ISO to help the camera see in the dark. If you're using a tripod or you have flash switched on, you can almost always keep the ISO set to 100.
SEE MORE: How to photograph light trails of cars
When should I start to increase my ISO settings?
You should use high ISO settings when you want to avoid blur. It's much better to put up with a bit of noise than end up with camera shake, so increase the ISO as far as you need to when you can't use a tripod.
Also, a higher ISO can be a good alternative to simply using flash. With flash you can stick with ISO100, but it can ruin the atmosphere (as shown in the middle of the three shots on the right).
A slow-speed approach
With many low-light subjects, it's best to use an ISO setting of 100.
This shot of a Polish market, for example, was taken indoors at night. But using a tripod, there was no problem in extending the shutter speed to get enough light to the sensor. This gave a bright enough exposure without even touching the ISO controls.
What is camera noise?
All digital cameras create a certain amount of noise in the images they capture. Noise looks a bit like the grain in a picture taken with film - you need to blow the picture up to see it. Fortunately, digital camera sensors are getting better and better at minimising noise.
Noise gets more noticeable as you increase the ISO setting. It's particularly noticeable in the darker shadow areas, and as well as a grainy texture, the blacks become mottled with colour.
This noise can be minimised using custom settings on your camera, or by using the options provided by image-editing software.
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