A Bit Beyond the Basics Part II: ISO

This time we are going to look at ISO in a little more depth.  The idea here is that you can, hopefully, take some new knowledge about ISO and apply it to the next picture you take.

An ISO number is a measurement of light sensitivity.  It was originally applied to different films, but on digital cameras it is a setting on your camera that tells the camera (and sensor) how much light-gathering capability it should apply.  A lower ISO number means that it will take more light to achieve the proper exposure and a higher ISO number means the camera will require less light to achieve a proper exposure.   Typical ISO ranges for a point-and-shoot camera are between 100 – 6400.  My camera has a range of 50 – 25,600 as do most DSLR’s.  A doubling of the ISO equates to a doubling of the light-gathering capability.  Remember that ISO is just one part of the exposure triangle so shutter speed and aperture also come into play depending on what you are trying to accomplish with your photo.  Listed below are some examples of when and how to use different ISO values.

ISO 50

This is an ISO I would choose if I were trying to capture a waterfall on a bright, sunny day and wanted it to look silky smooth to show the movement of the water.  The lower ISO means that the camera needs more light.  A proper exposure would require the shutter to stay open longer to compensate for the lack of light-gathering capability.  The longer the shutter is open, the longer the water moves across the frame and creates the blurred or silky look.  How long should the shutter be open to achieve this effect?  That depends on how fast the water is moving and how blurred you want the water to appear.  This takes some trial and error, but a shutter speed of 1/8 second is a good place to start.  It is important to note that you should use a tripod for this type of photography because you won’t be able to hold the camera steady for this length of time.


ISO 100

My camera is on this setting all of the time unless I need to change it for a specific photo.  Most of my photography is outdoors where there is sufficient light.  During the day, even a cloudy one, this setting allows my camera to gather enough light so that I can take photos without the use of a tripod.  When I shoot at sunrise and sunset I leave my camera on ISO 100 and use a tripod to keep my camera steady for the longer shutter speeds required.  Why not just change the ISO? The higher the ISO the more noise, or grain, in the photo.  I want my photos to be crisp, clear, and sharp without distracting digital noise.  A lower ISO results in a higher quality photo.


ISO 400

I rarely use an ISO above 400 and I only go this high when I don’t have another choice. Usually this occurs when I am taking photos of an indoor gathering.  While taking portraits indoors I could easily use a tripod and/or a flash and keep my ISO lower.  However, most family and friend gatherings consists of many people moving around the space and I want to be able to capture candid moments and not only posed moments.  I need a short enough shutter speed to prevent my subjects from being blurred.  Depending on activity levels, this speed will vary.  This also depends on aperture, your ability to hold the camera still, and the lens you are using.   For a photo of grandma and grandpa sitting on the couch, you can take a photo at a shutter speed of +/- 1/60 second.  Depending on the light in the room, you might be able to use ISO 200 for something like this.  For the kids moving around the room, you will need a much faster shutter speed such as 1/200th of s second.  The lighting, speed of the kids, your camera, and your lens will all affect the proper shutter speed but these are places to start.

ISO above 400

This is where your camera makes a big difference.  Unless you have a full-frame camera, any ISO above 400 will result in a somewhat grainy photo.  If you don’t know if you have a full-frame camera, then you probably don’t.  I knew nothing about this until I started studying photography in more depth.  Entry-level full-frame DSLR’s start at around $1200.00 and the lenses are even more.  Most people who own a camera like that know a LOT more than I do and won’t be reading this article.

So, why would you use and ISO higher than 400?  Primarily night photography.  Most point-and-shoot cameras will not be able to take a quality photo of the night sky.  It is fun to try, but don’t plan to come out of it with a photo you want to print.  If you have a high-end crop-sensor DSLR, you can get some night shots using and ISO around 3200.  You might be wondering why you can’t just use a longer shutter speed to gather more light so you don’t have to use a really high ISO.  You can – depending on what you want to capture. Generally speaking, any exposure longer than about 20 seconds is long enough to show the earth’s movement, meaning that your stars will be short blurred lines rather than sharp dots of light.  If that is what you are trying to capture, then that isn’t a problem.  If you want your stars to look like stars, then you have to keep your shutter speed around that 20 second mark by adjusting ISO and aperture.

Another complication of longer shutter speeds is that the camera sensor gets hot and creates digital noise.  So higher ISO and longer shutter speeds both create noise.  Both are needed for night shots.  These are some of the many obstacles that make night photography difficult.  Professional photographers who specialize in night photography usually have specific lenses and full-frame cameras to help minimize digital noise.  It is also possible to use editing software like Photoshop to help bring out the best in a night photo.

Other situations for higher ISO are simply those where nothing else will work and you want a photo.  This happens to me often when I have my point and shoot and no tripod.  If I see a beautiful sunset and all I have is my point-and-shoot or if my nephew starts walking for the first time when we are inside a dimly-lit room,  I will still take my photo knowing that I will never print it.  I just want to capture the moment as a memory.

In reality, all of my photos are taken to capture a memory.  If I think others would enjoy the same image, then I take special care to make sure to capture the shot in the best technical way possible.  However, there is a lot of freedom when I just pick up my phone or point-and-shoot.  It is easy to get caught up in all of the technical details and forget to enjoy taking photographs that make memories.  This is why I often take my point-and-shoot to family functions.  I am more free to participate in the gathering and capture candid moments when I am not obsessing about the light and camera settings.


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