Aperture priority is a digital photography basic which will enable you to gain control over how your pictures turn out



Aperture priority is one of the photography modes available on a DSLR camera which enables a photographer to adjust the depth of field in a photograph.

We have covered digital photography basics concerning shutter speeds, aperture settings, ISO and white balance in a previous page so you may click here to view that discussion.

In order to benefit from all the settings available on your camera you need to get to know and understand the different modes on the camera The best way to learn is to find out what settings there are and how to adjust them, then get your camera and ‘play’! Even if this doesnt seem to be a help to underwater photographers the basics are the same and basic understanding of your settings is what you need.

When you download images the settings used are visible when you right click the image and select properties if your image processing software doesn’t show this automatically.

I will explain the different modes to be used on your camera:

Aperture Priority

On an SLR camera you have a mode setting ‘A’ or ‘AV’. This is for aperture priority.



The changes in aperture size affect –



Depth of field

This is the term used for how much of the photograph subject is in focus.



You will read or hear terms like shallow focus, low depth of field – this refers to when a photographed subject like a portrait or an insect or flower – or in our case a small creature in photography underwater – is the only item in the picture which is in focus, the foreground and background are blurred.

Orangutan Crab (Achaeus Japonicus) on sponge
This is achieved by way of a lower f-stop number like f8 in this photo - note the blurred background - this indicates a shallow or low depth of field.

The aperture is large.

Remember low f-stop number means a large aperture, high f-stop number is a small aperture.



Underwater photographers - When deciding what depth of field you want the rule of thumb is:

Hypselodoris Bullockii




Landscape or similar usually needs a high depth of field therefore the whole scene is in focus.

A photograph of a single person or face, or a single animal or flower may be more effective with a low or shallow depth of field – only the subject is in focus.

If you set your camera to aperture priority mode you can then change the aperture setting whilst previewing the shot in the viewfinder.

If you start at a low number like f5.6 you will see that only the subject you are focusing on is in focus whilst the background or far background details are blurred.

Take a picture at that setting, then increase the f-number to f11, take a picture, then again increase the aperture to f22 and take a picture. More and more of the background comes into focus as you increase the f-number.

This setting also allows you to change your aperture setting without worrying about the shutter speed. The camera automatically adjusts the shutter speed to compensate for the changes in light created by the changing aperture.

Once you have played around with these settings download the pictures to your PC and then review the effects, they will be very obvious.




Now you know a bit about aperture priority click here to go back to digital photography basics


Click here to learn more about underwater photography


Click here to learn about using the shutter priority setting on your camera


Click here to learn about depth of field


Click here to learn how to read a histogram, an important tool on your digital camera


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