My first camera, a Brownie 127 took photos at f 14 and 1/50th with exposure control by not shooting in the evening or in the shade! My Canon Ftb allowed the photographer to set the aperture and shutter speed by manually aligning two needles to ensure the combination set would give the correct exposure. These were in the days of
Today DSLR or mirrorless cameras have a manual exposure mode like the Ftb and at least one automatic mode and two semi-automatic exposure modes as well as modes that combine automatic exposure with special settings for circumstances like sport, portraiture, snow and water.
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Should I use auto ISO for wildlife photography?
Yes. Many professional wildlife, portrait, and landscape photographers use aperture priority mode. It is often preferred over using shutter priority mode. However, shooting wildlife with AV mode does have its own unique cons and pros!
Aperture Priority
Aperture Priority automatically sets the shutter speed to ensure that the correct exposure is achieved with the aperture and ISO which are preselected by the photographer.
This essentially allows you to choose the style of photo that is taken by setting the depth of field via the aperture.
Small Depth of Field
A large aperture (a low f-stop number like 2.8 in the photo) gives a small depth of field allowing the subject of the photograph to be in sharp focus between out-of-focus objects in front and behind. The blurred background can, depending on the aperture and the lens, give very attractive soft abstract patterns of light and dark in a range of colors depending on the objects in the background. This is known as bokeh and is predominantly the reaction between light and the iris of the lens which affects the size and shape of the bokeh.
A small depth of field also tends to bring the focus of the viewer onto the animal as the background and to a lesser extent the foreground are not sharply focused.
image by Ian Sane on pxhere.com
As you or the animals move or a cloud passes over the sun your camera adjusts the shutter speed to ensure that each shot is properly exposed. The problem is that if the light starts to fade your shutter speed will drop and continue dropping until it goes too low and you lose sharp focus either through camera shake or the movement of your subject.
To overcome this you need to keep checking your shutter speed so that you can increase the ISO setting to compensate. But increasing the ISO too far risks quality deterioration.
Large Depth of field
A large depth of field keeps more of the image in sharp focus. A large depth of field is necessary if you are taking an environmental photo of your wild animal and need the background to show detail. It also helps in getting wingtip-to-wingtip shots of birds flying across you and in getting a larger group of animals or quickly moving animals in focus.
Correctly Exposed Photo
Aperture priority always gives a properly exposed photograph, unlike shutter priority where the camera continues taking underexposed shots when the aperture required for correct exposure is larger that the maximum of the camera.
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So you always have properly exposed shots even when the shutter speed becomes too low to achieve sharp focus. You can of course also boost the ISO periodically as this is easily done quickly and without interfering too much in the shoot.
Aperture Priority Prefered
This makes it clear that overall aperture priority will give better results than shutter priority and this is why almost all wildlife photographers used it on their film SLRs.
So yes you should use aperture priority for your wildlife photography although there is another technique that came with the introduction of digital.