Knowing Your Settings: ISO and the Exposure Triangle

ISO
ISO

In this tutorial, I will discuss what exactly does the ISO setting does to your images. I would recommend reading the previous posting if you haven’t. It would come in handy when we discuss what the exposure triangle is. You’re probably wondering, “What does ISO stand for?” Don’t worry, I’ve always wondered this too and it somehow stands for “International Organization for Standardization”… I’m not sure why it’s not IOS, but it’s ISO so that’s what we have to live with.

How It works

Have you ever used your camera phone in daylight and the photos turn out great but when you take a photo in a dark location, you get this color grain effect on your images? Often times you probably deleted those photos because the faces couldn’t be recognized or it was just terrible.  That has a lot to do with the sensor inside the phone’s camera. As I explained in the previous tutorials, the sensor is what records the image. So think of the sensor like film in a Polaroid camera. When you take a photo with a Polaroid, a film comes out and that film has a photo exposed onto it based on the shutter speed and apertures you chose. In today’s digital age, the sensor records the image and the screen on the back gives you the result of what the sensor sees. So it saves you the time that you would need to spend letting the film dry or getting it developed to see the image.

There are times where you would walk into a room and the aperture isn’t wide enough for you to achieve a shutter speed that is fast enough to capture motion. The room is just too dark. Lets say the settings you are at for this “room” is an aperture value of F/3.5 with a 1/15 seconds shutter speed at ISO 100. So what can you do from there? One option would be to use the flash on camera to give you addition light to freeze the action, but that often creates very point-and-shoot like images and aren’t very pleasing. The other option would be to adjust the ISO setting on your camera.

The ISO availability on each camera will vary. All DSLR sensors have a native range that the manufacture designates. This native range is considered to be the range that will give you the best image quality with the lease amount of noise or “grain” that often shows up at greater ISO settings. The images below will demonstrate what the grain looks like at various ISO settings.

Grain Comparision
Grain Comparision

As you can see, the lower ISO numbers will have the least amount of grain. The simplest way I can explain why this happens is to think of the sensor as if it were your eyes. During a bright sunny day, it’s going to strain and you’ll have to squint to make what you are seeing move visible. The sensor is the same. The harder it’s working to make the image visible, the more grain or “strain” will be apparent. ISO 100 means that the sensor is not working very hard because there is enough available light. On the opposite spectrum, ISO 6400 means that the sensor is working pretty hard in order for it to see the subject since there is not enough light available. This will vary between DSLRs since the technology in the sensor differs. I have two camera bodies, a 5d MK3 and a 7d. My 5d MK3 can reach to ISO 10,000 and produce usable images, whereas my 7d will give me usable images at ISO 6400. The reason is because the sensor in my 7d is older than the 5d mk3. There will always be advancement in this area of photography and eventually cameras will be able to shoot at ISO 25600 and produce usable images.

Choosing an ISO will really depend on what and where you are shooting. The amount of available light plays a huge role in this setting because it is the foundation that will give you the proper settings for your aperture and shutter speed. Of course this may vary depending on what affect you are looking for. When I’m shooting a wedding, the venue is usually indoors and very dim. I would have to set my ISO to 3200 or higher sometimes in order for my camera to achieve shutter speeds of 1/60 or faster. But if I’m photographing portraits outside in the bright sun, I can drop my ISO down to 100 since there is a lot of available light.

Exposure

So lets go over how all these things - aperture, shutter speed and ISO - come together when taking a photo. By combining the settings, we create an exposure for your image. The exposure refers to how bright or dark the image is after your click the shutter release and view the image on the back of the camera. Keep in mind that the back of the camera is NOT EXACTLY how the image looks like. The LCD, from my experience, if often brighter and has more contrast than what a computer screen would show. This is probably because software that is used to view the images. Keep that as a tip when you’re trying to judge a photo on the back of the screen. It’s often a good idea not to delete the photo unless you absolutely know that the photo is blown out, too dark, or out of focus.

The combination of the aperture, shutter speed and ISO is often referred to as the exposure triangle. In the illustration below, I will show you how this works. Imagine that each point of the triangle is a setting and the settings create an equilateral triangle. (If you don’t know what that means…it’s a triangle with all equal sides and angles.)

Exposure Triangle
Exposure Triangle

If I were to pull one point of the triangle, I would need to compensate for that adjustment somewhere else. Let say I have a perfect exposure at ISO 6400, F/2.8 and 1/125 shutter speed. Since ISO 6400 will give me a lot of noise, I want to bring that down to let say ISO 800. From 6400 to 800 is 3-stops of light that I am taking away (6400 to 3200 to 1600 to 800). So in order for me to achieve the perfect exposure at ISO 800, I would need to use the aperture or shutter speed to compensate for the drop in ISO. In most cases, the aperture of f/2.8 will be the lowest that a lens can achieve. Therefore, I will not be able to open my aperture any wider because it is maxed out. That means that the shutter speed will need to be adjusted by 3-stops…I hope I’m not losing anyone here. It can be confusing, but it will take some practicing to get use to. So from 1/125 I need to increase the brightness by 3-stops. That means from 1/125 I would go to 1/15 of a second to achieve the same exposure (1/125 to 1/60 to 1/30 to 1/15.) So lets recap the settings. We started off at ISO 6400, f/2.8 and 1/125 second and ended up with ISO 800, f/2.8 and 1/15 shutter speed. These two exposures will be exactly the same because we took the ISO from 6400 down to 800, which cuts the light down, and slowed the shutter speed down from 1/125 to 1/15, which increases the light back up.

Exposure Comparison
Exposure Comparison

It is really like a balancing game when it comes to the exposure of an image and the settings. At events such as weddings and parties, it can become very hectic in your mind if you don't have these basic understandings down. Once you step into a room, you need to be able to guess the setting and make small adjustments from there. Like I mentioned earlier this isn’t something that you will achieve in a day, it will take time and don’t be discourage if you don't understand it the first time. My advice would be to continue to shoot and see what you come up with.

The best way to use all three setting independently is to switch to Manual mode. It’s the M on top of your camera. This will allow you to adjust all three settings manually to achieve the exposure you want. This is what I currently use majority of the time, but in the end it doesn’t matter what mode you’re on just as long as you make a picture. Until next time, keep on clicking!

ISO 10,000 f/2.8 1/80 sec
ISO 10,000 f/2.8 1/80 sec
ISO 100 f/10 15 sec
ISO 100 f/10 15 sec
ISO 3200 f/3.5 3.2 sec
ISO 3200 f/3.5 3.2 sec
ISO 2000 f/2.8 1/160 sec
ISO 2000 f/2.8 1/160 sec
ISO 2000 f/1.6 1/80 sec
ISO 2000 f/1.6 1/80 sec
ISO 1600 f/5.0 1/60 sec
ISO 1600 f/5.0 1/60 sec
ISO 1000 f/2.8 1/800 sec
ISO 1000 f/2.8 1/800 sec