Aperture ISO and Shutter Speed
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Mastering Aperture ISO and Shutter Speed

I’ve been meaning to write this article for years now, but never got around to it as the weather here in Spain keeps me outdoors, shooting! The unholy trinity of Aperture ISO and Shutter speed. Three settings that are inextricably linked together and absolutely determine how your photograph will turn out.

An overview of this subject, entitled How to Capture Motion in Images related to modern mirrorless cameras can be found on the Canon website.

When I worked as a commercial photographer I always used manual settings, starting with the assumption that ISO should be 100 (I use Canon cameras), choosing my lens and aperture to suit the style of shot, and adjusting shutter speed to whatever it needed to get a good exposure. Of course in the studio I used lights, so I was able to increase or decrease the amount of light at will. So it was always possible to get a good exposure with sharp focus and as much depth of field as I needed.

As a landscape photographer though, things are different. I rely on the sun for light and I can’t control that. Objects in the frame move around of their own free will and taking a photograph depends on waiting for the best light and finding the optimal composition as well as the best creative effect.

This is where I started to explore automated modes and presets, in particular Aperture Priority.

Let’s take a look at each element of the triumvirate and see how they work together.

The Problem

Photographic images are made from light. There’s no getting around this, we have to have enough of it to make a good exposure, too much of it will ruin the image. Photography is a balancing act.

ISO

For an in depth article on ISO check out my article Understanding ISO in Digital Photography, where I discuss every aspect of ISO.

For this article, think of ISO as an amplifier of light. The light it amplifies is not, unfortunately the light streaming through the lens, it is the light recorded by the sensor. There is a subtle difference. When we add amplification to the light recorded by the sensor we introduce noise.

ISO increases numerically, each increment (here) doubling the amount of light.

100 – 200 – 400 – 800 – 1600 are 1 stop increments.

Modern cameras have steps between the stops. So my Canon 5Ds has

100 – 125 -160 – 200 – 250 – 320

Modern digital cameras are much better at handling noise than the early models but it can still cause us problems. As a rule of thumb the best quality of image with the best color and highest dynamic range is made at the lowest number in the ISO dial. Assuming you have enough light.

Aperture

Aperture refers to the blades in the lens that wide open allow a lot of light through and closed down, very little. In addition to controlling the amount of light, because this is a physical arrangement determining in part at least, how the sunlight strikes the sensor it also controls depth of field.

Aperture is also measured stops and as in ISO, each stop, doubles the amount of light. The actual numbers are confusing as they relate to multiples of 1.4. Lenses are circular so increasing the diameter by 1.4 doubles the area of the aperture.

f/1.4 – f/2 – f/2.8 – f/4 – f/5.6 – f/8 – f/11 – f/16 – f/22 are 1 stop increments.

So if I had only ISO and Aperture to play with, I could introduce more light by increasing the level of ISO or by opening up the aperture. The first may introduce noise, the second may alter my depth of field. Note that opening the aperture by 1 stop and decreasing the ISO by 1 stop will produce the same exposure. But the depth of field will be shallower.

Creative use of Aperture

The principle creative tool in the photographer’s box is depth of field. In commercial photography depth of field is massively important, the need to separate the subject from the background is fulfilled by having a pin sharp subject and a soft, out of focus background. This is achieved in small spaces like studios by having a wide aperture.

In a normal lens, f/2.4 is considered a decent setting for a shallow depth of field. With a macro lens that might only be a couple of millimetres of sharpness. Which is why photo forums are filled with would be product photographers asking questions about lenses, focus stacking, and so on.

Rule of Thumb

The area of sharp focus is relative to the distance from the subject, but it is roughly 1/3 of the area in front of the plane of sharp focus and 2/3 of the area behind. So a wide aperture might produce an area of sharp focus in front of a close subject of 1 inch and 2 inches behind. Note that I use the term plane of sharp focus instead of point. The plane is curved, how much depends on the lens.

At large distances this becomes insignificant because 100 metres in front of an object and 200 behind will simply produce a sharp photo.

The art of getting true front to back focus is related to the hyperfocal distance so if I use my 100mm lens with an aperture of f/1.5 my hyperfocal distance – ie. the spot where I place the focus is 221.98m. This should give me sharpness throughout the frame.

Many landscape photographers prefer to use focus stacking to achieve the same result, moving the plane of focus and combining the images later.

Shutter Speed

The third adjustment is Shutter Speed. This determines the length of time the shutter is open for and is measured in fractions of a second.

A full stop down in terms of shutter speed is double the original shutter speed.

1/100 – 1/200 – 1/400 – 1/800 are 1 stop increments

So if I start at 1/100 of a second and want a full stop less light, I must move to 1/200 second. That movement would be compensated for by introducing an extra stop through the Aperture or ISO.

So a very effective method of reducing or increasing the amount of light reaching the sensor. Naturally there is a downside. Leaving the shutter open introduces blur on any moving object and also as a byproduct of camera movement. Which is why I like tripods.

Creative Use of Shutter Speed

Shutter speed can also be used creatively. Blur accentuates the perception of movement so when shooting racehorses or fast cars, a little bit of blur is a good thing. How much can only be learned by experience but a useful guide is this.

Rule of Thumb

Handheld shooting with a modern full frame camera, in most circumstances produces a sharp photograph at twice the reciprocal of the focal length. For example if I shoot with a 50mm lens then I can count on my photo being sharp at 1/100 second.

Using the same lens, if I shoot a moving object like a bird or a runner, then to achieve sharpness I need to shoot at 1/500 second.

With the same lens, if I myself am moving and the subject is moving (think photo safari) then I need to go to 1/4000 second. (figures from Canon UK)

In the old days, when sensors had low pixel counts the rule was the reciprocal of the focal length, twice the reciprocal for slow moving objects and twice that for fast moving objects. Easier to remember but doesn’t work on cameras with 50Mp sensors.

What Does this Mean in Real Life?

What this boils down to is that the photographer needs to be aware of the requirements of the image and choose the settings that will deliver that shot.

So, for example if I’m shooting a landscape, I generally want it all to be in focus but I might for creative purposes want to see some movement in windblown grasses in the foreground.

This would mean a smaller aperture – I prefer not to go much over f/11 as smaller apertures introduce their own problems such as diffraction. It would also require a slower shutter speed – I don’t want to freeze the grasses so I might go to something around 1/50 second. You may then find that you don’t have enough light so the remaining option is to bump u the ISO.

Let’s take another scenario. I’m shooting a still life with a 50mm lens from a short distance away. I’ll choose a very wide aperture in order to throw the background out of focus. I will then use the shutter speed to reduce the amount of light hitting the sensor.

Video

Deliberate Photography

Deliberate photography is all about making the right decisions at the right time. It’s about lens selection, tripod selection, focal length and aperture.

Because the first hurdle is the technical hurdle, we need to realise that a good exposure can be arrived at in different ways, but only one of those ways gives you a good photograph from the artistic perspective. Put another way, It’s only by understanding the rules that you can make good creative decisions. Deliberation has been my mantra for all the years I’ve practised photography in the hope that I can take fewer pictures but get more “keepers”.

Priority Modes

On Canon Cameras the Priority modes are marked as

  • Manual – You are in full control of Aperture, ISO and Shutter Speed
  • Av – Aperture Priority – You set the required Aperture and the camera calculates shutter speed and ISO (assuming you have ISO set to Auto)
  • Tv – Shutter Priority – You set the shutter speed and the camera calculates Aperture and ISO (assuming you have ISO set to Auto).
  • P – Program – The camera makes all the choices.

In the case of Av and Tv, you can set the ISO so that the camera only uses the remaining option to balance the exposure.

More Rules of Thumb

The longer the focal length, the more likely it is that you’ll need to increase the shutter speed to compensate for shaky hands. The weight of the camera/lens combination and the distance between the camera and the subject conspire to magnify the slightest movement. This is another reason why I use a tripod.

Av is often used in landscape photography to ensure the sharpest exposure. For most lenses this will be in the range of f/5.6 – f/11.

Similarly with focal length, using a Zoom lens the sharpest image will be found in the middle of the range of focal length. So 100-400mm lenses shoot best at around 300mm

Aperture ISO and Shutter Speed – Conclusion

For beginners, grasp the idea that at any given ISO, a wider aperture requires a faster shutter speed to create the same exposure. Reduce the shutter speed, add more light, balance it by reducing the size of the aperture.

Intermediate photographers will want to understand the figures behind stop calculations. Doing so leaves less to chance and introduces more deliberation.

Advanced Photographers will know the figures inside out and apply them in a second!

A final rule of thumb is to start with a set ISO (100 on a Canon camera) determine which of freezing the motion or reducing the depth of field is more important and start with Shutter speed or Aperture accordingly – only increase the ISO if you need more light after you’ve set the Aperture and Shutter speed.

Understanding ISO in Digital Photography

Understanding Aperture

.Mastering Aperture in Landscape Photography

Simplifying Hyperfocal Distance

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