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Photography

Introduction to ISO, Aperture and Shutter Speed

Short answer: Aperture controls depth of field, set a low f-stop for background blur or a high f-stop to have most of your scene in focus. Use a fast shutter speed to freeze motion, or slow shutter speed and tripod to let more light in. Use the lowest possible ISO for crisper images, or bump this up for a brighter but grainer image.


ISO

ISO is an exposure index that indicates how amplified the signal from your digital image sensor is. Any noise or grain present in your image will be amplified at higher ISO values and be much more obvious:

ISO 100 Sample Image
ISO 100, 1/320 sec, f/9, 50 mm
ISO 1600 Sample Image
ISO 1600, 1/2500 sec, f/13, 50 mm
ISO 25600 Sample Image
ISO 25600, 1/4000 sec, f/36, 50 mm

In general you will want to keep this value as low as possible in order to achieve sharp and clear images.

This is also an important factor to bare in mind when buying your camera. Look for the lowest value that can be achieved with the camera you are looking to buy and ask yourself if this is going to be good enough for you.

Also, the more expensive the camera the better it should be at producing a good image at higher ISO values. Scrutinise the sample images available and take note of the settings used to achieve each image. For more info check out our ISO post.

Aperture

This is the size of the opening in the lens. This is measured in f-stops. The smaller the number the larger the opening and the more light that will be let in, the higher the f-stop the smaller the opening and less light will be let in.

The key effect to keep in mind with aperture is depth of field. A low f-stop has a shallow depth of field. This creates background blur that is very popular in portrait photography and is an easy way to give a photo a professional look.

f4.5 sample photo
1/160 sec. f/4.5 26 mm ISO 100
f10 sample photo
1/30 sec. f/10 26 mm ISO 100
f20 sample photo
1/8 sec. f/20 26 mm ISO 100

A higher f-stop has a deeper depth of field meaning more of your scene will be in focus. This will be more common in landscape photography if you want both foreground and background to be in focus.

Aperture is key to bare in mind when buying lenses. You will notice more expensive lenses are the ones that can shoot at low f-stop values like 1.4. This is going to be valuable if you want to shoot handheld in low light conditions and want to create background blur.

Shutter speed

This is the time your shutter is open. My Sony A6000 can shoot as quickly as 1/4000’s of a second.

A quicker shutter speed is letting less light in but more capable of freezing action. For quick action, like sport or a bird in flight, you might want to use a fast shutter speed if you want to freeze the motion in the photography.

A slower shutter speed lets more light in but movement, in the subject or from you holding the camera, is more likely to blur.

1600th of 1 second shutter speed sample image
1/1600 sec. f/3.5 16 mm ISO 100
4th of 1 second shutter speed sample image
1/4 sec. f/22 16 mm ISO 100
1 second shutter speed sample image
1 sec. f/22 16 mm ISO 100

Balancing priorities

The settings you use will depend on the image you are looking to achieve. Think about what setting you should be prioritising and let the other settings follow this led.

An easy way to do this is to use the priority settings on the camera. For example, if you want a blurred background then use aperture priority and set the f-stop to the lowest value your lens is capable of. If you want to freeze motion then use shutter priority. On my Sony A6000 I’ll often use Program Auto to set the ISO to 100, for crisp images, and let the aperture and shutter speed be set automatically.