The exposure triangle and wildlife/bird photography

I received a question from a friend regarding the high ISO I am using in my wildlife and/or bird photography. So I decided to write a short post on the exposure triangle to explain the concepts I am using and hopefully it will explain why I do some an ISO for certain photos.

1.         Exposure triangle

I do use the well-known exposure triangle when I consider taking a wildlife/bird photo. The three main controls for adjusting the amount of light (exposure) in any images are:

• Shutter Speed
• Aperture
• ISO

As you can see, Shutter Speed is one of the three pillars of photography, the other two being ISO and Aperture. Shutter speed is where the other side of the magic happens – it is responsible for creating dramatic effects by either freezing action or blurring motion. Therefore, it is important to decide beforehand what your aim with a photo is:

• Will it be a record photo and/or a stationary bird?
• Will it be a bird in flight?
• How much blur do want in your photo?

2.         Aperture mode

But let us take a step back. First, you need to decide which camera mode/priority you want to use when shooting wildlife/birds. When I started taking photos about 3 years ago with a bridge camera, I’ve only used the “Automatic” mode/priority because I did not understand the other settings. Automatic means the camera itself decides which shutter speed, ISO and aperture are the best for the conditions/the specific photo you want to take. The Automatic mode is great for beginner but not if you want to play around with the photo.

Nowadays I do use the Aperture mode of my camera most of the time when shooting wildlife/birds as are many other great photographers (Manual for landscapes). It is very helpful especially if the action is fast and one needs fast re-actions/reflexes.  All it means is, when I shoot in Aperture mode/priority, the first thing you need to decide/set is the lens aperture and it will depends on what I want to photograph. Then the camera automatically sets the shutter speed. In Aperture mode, I cannot directly set the shutter speed. But what does it mean if I am setting the camera’s Aperture first?

Remember that Aperture is one of the three pillars of photography and of the exposure triangle. Therefore, exposure is one the main issues to consider when it comes to wildlife/birds photography.

Let us get back to Aperture. The aperture of a camera (how big or small the lens diaphragm inside a lens opens up) allows different amount of light to fall onto the sensor of your camera. Aperture adds a dimension to a photo as it determines the area which will be in focus (the depth of field) for example the aperture can be used to blurring the background behind your primary object (e.g. at f2.8) – the bird  or it can bring everything in focus (e.g. f16).

To summarise; the size of the aperture has a direct impact on the depth of field, which is the area of the image that appears sharp.

• A small opening is reflected in a large f-number for example f22, (called a small aperture) and it will bring all foreground and background around objects in focus. I do use such f-stops in landscape photography.
• A large opening is reflected in a small f-number.  A small f-number for example f4 (called a large aperture) will isolate the foreground with your object (the bird) from the background by making the foreground and object look sharp while the background will look blurry. When we consider exposure and Aperture, larger aperture means that the lens can pass through more light, and hence, your camera can capture images faster in low-light situations. Having a larger maximum aperture also means better ability to isolate subjects from the background.

An easy way to remember the Aperture function:

•  Small opening – big number – small/narrow depth of field (Small-big-small)

• Big opening – small number – big/wide depth of field (Big-small-big)

3.         Shutter speed

The next pillar to consider is the shutter speed but I am not going into the detail of the shutter speed. Only the fact that if you want to freeze all the movements/actions, you need a fast shutter speed (e.g. 1/1000 sec) and if you want a blurry effect, you need a slow shutter speed (1/30 sec).

Just the following piece of advice regarding shutter speed:

• Looking at shutter speed in isolation from the other two pillars of the exposure triangle (aperture and ISO) is not really such a good practice. Once you decide on a specific shutter speed or if you want to change the shutter speed, you’ll need to change one or both of the other pillars to compensate for the change in shutter speed but still get a well-exposed photo. For example if you change your shutter speed one stop (for example from 1/125 sec to 1/250 sec) you’re effectively letting half as much light into your camera. To compensate for less light coming into the camera you’ll probably need to increase your aperture one stop (for example from f16 to f11).

• Focal Length and Shutter Speed – as a side line – another issue to consider when choosing shutter speed is the focal length of the lens you’re using (e.g. 20mm lens). Longer focal lengths will accentuate the amount of camera shake you have and so you’ll need to choose a faster shutter speed (unless you have image stabilization in your lens or camera). The ‘rule’ of thumb (to use with a lens of a specific focal length if no image stabilized system is used) is to choose a shutter speed with a denominator that is larger than the actual focal length of the lens. For example if you have a lens that is 200mm, shutter speed of 1/250th would be acceptable but not a shutter speed of 1/60sec.

To summarise the issue of the shutter speed:

• You need to develop your own style of photography.  The two major determining factors assisting you to make a decision on the shutter speed are (a) your style of photography, and (b) what you wish to photograph.

• Looking at the above-mentioned two pillars, it is acceptable to assume that both the aperture and shutter speed control the amount of light that reaches the sensor of a camera. Therefore, there is a very strong relationship between the two pillars. So, with aperture and shutter speed, the objective is to control and regulate light reaching the camera’s sensor in order to have a proper exposed photo.

4.         ISO

Therefore, as the name suggets – there should be a third pillar in the triangle. Just to complicate matter? No not really as it is not so complicated if you do understand all the pillars and go out to practice a lot. Now, not to confuse you – let us rather go back to the exposure triangle and complete the third pillar of the exposure triangle namely ISO.

ISO is the measure of a digital camera sensor’s sensitivity to light. With aperture and shutter speed, one can control and regulate the light coming through the lens to the camera but the sensor’s sensitivity for the light can vary.

Let us look at the following scenario (in bird photography) and apply the principles discussed above:

• Say for example you saw a large raptor sitting on a bush and you’ve decided that you want to us an f-stop of 5.6 in order to get the entire bird in focus – especially if it is a large raptor. An f-stop of f2.8 will probably blur the wings (what we call “soft wings”) of the raptor if you are too close to the bird. You decided that you want to catch the bird in its take-off (BIF = bird in flight) and for that you need a fast shutter speed (e.g. 1.3200sec). Such a fast shutter speed will freeze the moving wings and other actions of a large raptor in flight. Also, it is very late in the afternoon and there isn’t much light left.

The implications of your decisions/settings:

• A fast shutter speed (1/3200sec) is letting in less light (and already there isn’t that much light available) and therefore, your photo will be underexposed and you might get clipping of the darker areas with the loss of detail in that areas on the bird. And that is a “total no-no” in wildlife photography.
• Therefore, you need to compensate in order to get more light to the sensor of the camera and get a well-exposed photo.
• One way to compensate is to increase the aperture (bigger lens diaphragm opening = smaller f number = f2.8) and that will allow more light to reach the sensor.
• In Aperture mode, if you increase your f-stop van f5.6 to f2.8, your shutter speed will be changed from 1/2000 to 1/3200 – the desirable effect. BUT (and it is a major BUT) the larger aperture will result in the creation of a less depth of field and the wings of the raptor will be out of focus. And that is not what you want. And that is where the third pillar namely ISO comes into play.

The higher you set the ISO of your camera, the more sensitive is the sensor for light meaning less light is necessary to capture a well exposed image. So, ISO200 is twice more sensitive than ISO100, while ISO 400 is twice more sensitive than ISO200. This makes ISO 400 four times more sensitive to light than ISO100, and ISO1600 sixteen times more sensitive to light than ISO 100, so on and so forth. What does it mean when a sensor is sixteen times more sensitive to light? It means that it needs sixteen times less time to capture an image! Look at the scenario below:

ISO         –    shutter speed example:
ISO100      – 1/400 of a second
ISO200     –1/800 of a second
ISO400     – 1/1600 of a second
ISO800     – 1/2000 of a second
ISO1600   – 1/3200 of a second
ISO3200  – 1/4000 of a second

In the above scenario, you’ve set your camera in Aperture mode and decided to use an Aperture of f5.6 for your shot. Your camera sensor needs exactly 1/400 of a second to capture a well exposed image at ISO100 for/at that f-stop (f5.6). But you need a shutter speed of 1/3200 sec for your shot to freeze the movements. Now, by simply switching the ISO from 100 to an ISO of 1600 (and keeping the aperture (field of depths already determined) at f5.6), you can get the desired shutter speed of 1/3200 of a second and you can capture the same scene at the desired shutter speed (1/3200 of a second) to freeze the movements/actions and keeping the depth of field at the desirable level.

To summarise – when to increase the ISO on your camera:

You should increase the ISO when there is not enough light coming through for the camera to the sensor as you have already a pre-determined aperture (field of depth) and shutter speed (to freeze the movements). But before increasing the ISO, you should think about your ISO level as the increased ISO levels will introduce noise to our photo. Once again you can the question: “Why not keep the ISO at 400 or 800 all of the time? Just remember, the lower the ISO, the better the quality of the photo. That is why I usually try to shoot at the lowest possible ISO.

5.         Exposure compensation factor

In order to shoot at the lowest possible ISO, I also use the Exposure compensation factor. When shooting in the Aperture mode, one can increase the Exposure compensation factor (the + or – setting) on your camera as a fourth possibility to get a well-exposed photo.

Once I’ve decided on my Aperture (e.g.f5.6) and my desired ISO level (e.g.800) and I know I want a shutter speed of 1/3200sec, I set my camera on Aperture priority, set my Aperture at f5.6, set my ISO at 800 and then I use the Exposure compensation to get the predetermined shutter speed of 1/3200.

6.         Summary

To summarise:

First I need to decide what kind of photograph I want to take:

• Do I want to freeze the action – high shutter speed (e.g. 1.3200sec)
• Do want a blurry effect – slow shutter speed (1/30sec)
• What is the quality of the light in the environment/surroundings? (use all three pillars of the exposure triangle to get the best possible shot (quality-wise).

Please read my other blog on wildlife and bird photography tips:

http://willemkrugerphotodiscuss.wordpress.com/

Any comments are more than welcome but rather keep on shooting until you’ve developed your own style.