Aperture Priority vs Shutter Priority? Whether you’re a fan of Aperture Priority or Shutter Priority, you are enjoying the semi automatic priority settings of a modern digital camera. For a wedding photographer, settings are made on the trot. I believe that the simplest approach gives the most reliable result.
Let’s take a step back. Unless you are a tech giant with an oversized brain, many photographers start shooting in Auto mode then wonder why images may be under or over-exposed. Maybe you don’t produce additional effects such as blurred background, bokeh or perhaps moving objects are blurred. Conversely you may want to create an image with moving objects blurring to provide that movement effect.
Auto mode can stifle creativity. Keep in mind that auto mode will give a median result that will cover a multitude of situations.
International Standardization Organization (ISO)
There is another shooting variable that cannot be ignored. Yes ISO. Aperture + Shutter Speed + ISO = Exposure. Adjusting any of these variables changes the outcome.
ISO dictates the sensitivity of the of the electronic image sensor to light. A low ISO setting needs more light to achieve good exposure but produces a fine grain image. High ISO needs less light but produces a grainy image.
In bright light a low ISO is ideal. As the light diminishes so does the cameras ability to capture sharp images of moving objects. For example, a bride throwing a bouquet in poorly lit conditions will produce a blurry result unless the shutter speed is set accordingly. This is where ISO can limit shutter speed option.
On most digital cameras, the ISO can be fixed or set to Auto. In some cameras the Auto ISO will also have a ceiling ISO setting. This is a huge step forward from film cameras where you had to change the film in the camera to change the ISO.
Aperture Priority Mode
The iris in your eye opens or shuts according to the lighting intensity. Bright light, narrow iris.
There is an adjustable screen inside each lens called the aperture which works on the same principal. The aperture effects both the exposure and the depth of field. Wider aperture, the more exposure and the less depth of field. In conclusion, the aperture is used to reduce or increase the image exposure and conversely the depth of field.
Aperture is a portrait photographer’s weapon of choice. Frequently the aim is to keep subject in focus but blur the foreground and background. This is where a large aperture of say f/2 is used to produce a shallow depth of field.
The landscape photographer will have a different objective. An appealing landscape will usually have a sharp foreground and background. This requires a very wide depth of field achieved with a narrow aperture say f/22.
The confusing bit is that a large aperture is represented by a small number e.g. f/2 and a small aperture by a large number e.g. f/22.
Shutter Priority Mode
Shutter Priority fixes the shutter speed. I believe this is the key point of the Aperture Priority vs Shutter Priority. Light only enters the camera when the shutter opens. The amount of time that the shutter opens is determined by the shutter speed setting. Faster shutter speed, the less light hits the image sensor in the camera and the less blurring due to moving objects or camera shake.
With shutter speed settings the photographer has control of not only exposure but can choose to show movement (motion blur) . Simply dial a long exposure or freeze moving objects with a fast shutter.
A tripod is required for longer exposures (such as achieving a silky look with flowing water) so that the rest of the image is sharp.
The Hand Held Rule
Fortunately there is an easy Hand Held Rule for setting the shutter speed for hand held shots. This is a boon for shooting where a tripod is impractical.
The Hand Held Rule for Full Frame hand held cameras is to set the shutter speed denominator equal to or higher than the focal length. For example, shoot equal to or faster than 1/200th second for a 200 mm lens.
To be on the safe side, set the shutter speed for ‘Crop Sensor’ cameras one stop faster than the Golden Rule above. For example shoot at 1/25th second for a 200 mm lens. This may be a bit of an overkill when shooting with a steady hand as camera shake is not an exact quantity.
An advantage of using Shutter Priority mode is that for hand held shots, camera shudder is effectively eliminated by maintaining a minimum shutter speed. At the same time, the depth of field is reduced by increasing the shutter speed from this base.
There is no single solution for all situations with the Aperture Priority vs Shutter Priority argument but once the pros and cons are understood the choice is mostly straight forward.