I have found that one of the most frequently asked questions by guests whilst out on safari is “What ISO should I be shooting at?”. This is not always a simple question to answer because it depends on a number of variables which, unless composition, camera body, lens, exposure compensation value and composition is the same, will vary between each guest.
Inevitably my answer revolves around giving the guests a basic understanding of what ISO is and how it affects your images. Something I thought I would share in this post for everyone!
What is ISO
Without going down a long and very technical road (a road that I must admit even I am not too familiar with) ISO refers to the sensitivity of your camera to light. Small numbers (eg. Iso 100-400) represent a less sensitive state whilst higher numbers (eg. ISO 800 +) represent an increased sensitivity to light.
ISO is essentially a function of your cameras sensor and by increasing the ISO value (higher numbers such as ISO 800 +), your camera can capture images in low-light environments without having to use a flash or freeze action in low light conditions as a result of the increased shutter speed (stay with me here, I will expand on this shortly).
Most cameras today will have have ISO values that start at around 100 or possibly 50 and increase up to in excess of 250 000 depending on your camera model. An ISO value of 100 means that the sensor is twice as sensitive to the available light than an ISO value of 50. Similarly, an ISO value of 200 is twice as sensitive to light than an ISO value of 100 and so on and so forth. Being able to manipulate ISO values on the fly and to the extent that we can, has revolutionised wildlife photography as we are now able to photograph subjects in low light conditions without a flash by simply increasing the sensitivity of the sensor to light (increasing our ISO value).
Sound too good to be true? Well there is a down side to photographing at higher ISO’s.
What is Noise
If you are of the opinion that noise is how quietly your camera operates then pay attention please!
When we increase our ISO values we are introducing digital noise into our images. If you are interested in finding out how and why noise is created then you can check out this post, but for the purposes of my post it is enough to understand that the camera achieves this “increased sensitivity” by amplifying the image signal in the camera. However, this also amplifies noise and so, higher ISO values will produce progressively more noise.
Got it? Good.
“Image noise” is the digital equivalent of film grain for analogue cameras and this typically increases with the sensitivity setting in the camera, length of the exposure, temperature, and even varies amongst different camera models.
In the example below, you can clearly see the grain and colour noise in an image shot at ISO 6400 on a Canon 1D MKIV under extremely low lighting conditions with a 300mm F2.8 lens @ f2.8 and a shutter speed of 1/20 of a second.
These days noise can be dealt with pretty well in post processing programs such as Lightroom where both grain (luminance noise) and colour noise can be removed pretty easily. Why did I choose to shoot this subject at ISO 6400? The answer is simple, I needed the camera to be as sensitive to light as possible in order for me to achieve a fast enough shutter speed to render my subject sharp and in focus.
1/20th of a second whilst using a 300mm lens is far from ideal but it worked, and leads me into the next section on how ISO affects shutter speed.
ISO, Shutter Speed & Aperture
If we take the scene above and assume that I picked up the camera and dialled in an aperture value of 2.8 (wide open to allow as much light in as possible) and an ISO value of ISO 1600, pointed at my subject and got a shutter speed value of 1/5th of a second. Not good enough considering I theoretically need at least 1/300 to eliminate any camera shake.
Next step, rest the camera on something steady to eliminate as much camera shake as possible. Increase ISO to 3200. Resultant Shutter Speed = 1/10th of a second. Still not good enough.
ISO up once again to ISO 6400. Resultant Shutter Speed = 1/20th of a second. Not ideal but I am already starting to push the limits here and may be able to get a proof shot to share around the campfire later that evening.
Assuming that my aperture value, composition, and ambient light remains unchanged each time I double my ISO value my shutter speed halves (becomes faster). Here’s an easier example:
- ISO 100 – 1/2 a second
- ISO 200 – 1/4 of a second
- ISO 400 – 1/8 of a second
- ISO 800 – 1/16 of a second
- ISO 1600 – 1/32 of a second
- ISO 3200 – 1/64 of a second
Okay so by now you should understand that higher ISO’s will provide you with a means of manipulating your shutter speed without having to change your aperture value, baring in mind that we ideally need at least 1/focal length to eliminate any chance of introducing camera shake into our images, making ISO an incredibly useful tool to achieve sharp images.
Sure, we will have to deal with digital noise in images taken at higher ISO values but having a “noisy” but sharp image of a once in a lifetime sighting is better than having a blurred image of the same sighting without noise wouldn’t you agree?
So, what ISO should you be shooting at? Here’s a great piece of advice to keep in mind:
Your ISO value should be as high as necessary, but as low as possible…
That is to say that you should always aim to have a shutter speed of at least 1/focal length unless you are trying to convey a sense of movement in your image (this is a well known guideline). If you find that your shutter speed is much faster than this theres a good chance that you can decrease your ISO values which will reduce your shutter speed and simultaneously reduce the amount of digital noise in your image. It’s all about finding that optimum point where shutter speed and image quality meet.
ISO in the Field
This is a lot to digest but I hope that the hypothetical situations and graphs below will put this theory into context in a more visual manner.
Ambient light is the primary factor which will determine what ISO value you will be using. We know that under good lighting conditions we can use lower ISO values where the camera is less sensitive to light. Conversely, if you are photographing under low light conditions you will need to increase the cameras sensitivity to light.
Assuming you are aiming for a constant shutter speed, lets say at least 1/focal length, your ISO values during a full day game drive might look something like this depending on the weather conditions.
ISO values start off rather high (800) in the early morning but, as the sun rises and more ambient light is available, these values can be lowered (200). On an overcast day, when the amount of light is less than on a sunny day because of the diffused light brought about by cloud cover, ISO values will typically be greater than those needed on a sunny day. Once the sun sets, ISO values will need to be increased dramatically to cope with the low light conditions – even when photographing in an ethical manner with the aid of a spotlight.
We know that aperture has a direct impact on the amount of light which falls onto the sensor, and therefore the resultant shutter speed. Assuming we are aiming for the same constant shutter speed using the same focal lengths, the graph below shows how ISO values could vary between a photographer using a lens with a maximum aperture value of f5.6 and a photographer using a maximum aperture of f2.8.
The photographer with the f2.8 lens is allowing four times as much light to fall onto his sensor than the photographer with the f5.6 lens. If both photographers are to achieve the same shutter speed, the photographer with the f5.6 lens will need to shoot at an ISO of two full stops higher than the photographer with the f2.8 lens. Notice how much of a difference there is in ISO values used in low light conditions!
This is a great example of how lenses with large apertures such as f2.8 not only provide a shallower depth of field, but an opportunity to photograph at lower ISO’s under low lighting conditions when compared to lenses with a maximum aperture of f5.6.
To wrap it up
This is a lot to process! The main points here are as follows:
- ISO. As High as necessary and as low as possible!
- Don’t be afraid to photograph using high ISO’s.
- Always purchase the best possible quality lenses and go for the largest aperture possible.
- Manipulate your ISO values to achieve the desired shutter speed and eliminate camera shake.
- New sensor technology and software allows you to remove a lot of the digital noise associated with images taken at high ISO’s.