All about ISO

So in the past few weeks we’ve learned about how aperture and shutter speed affect the amount of light that is let in or kept out of your camera.  Aperture also controls your depth of field and shutter speed helps to define motion, but for today, we’re going to be to talking about light.  Photography is all about light, and you can’t fully understand that until you understand how ISO works into the picture.

ISO stands for  International Organization of Standards, but you really don’t need to know that.  What you do need to understand is that ISO is the part of the equation that tells your camera how quickly to capture the light it’s exposed to.  In the days of film (or for those of you following along using film cameras), ISO is actually the speed of the film.  In the digital world, ISO is referring to your digital sensor.  The lower your ISO setting (100 speed, for example), the slower the exposure of light onto the film or image sensor will be. The faster the ISO (1000 speed, for example) the faster the exposure of light onto the film or sensor will be. 

For quick reference, here’s a generic ISO reference chart. Don’t be jealous of my crazy free hand photoshop skills. 😉 Hey, I’m a photographer not a graphic designer!

On all  DSLR cameras, as well as some point and shoot cameras, you can adjust your ISO setting for each shot you take. As a general rule, for bright outdoor shots, choose a number between ISO 200 and 400 speed. When you move to a setting with less light, such as when you go indoors, you can quickly increase your ISO to 800, 1000, or higher to keep on taking photos.  Just remember that the quality of your pictures will change depending on the ISO you use.  A very low ISO will result in a crisp, clear image while a higher ISO will create more digital grain or “noise” in your picture.

To explain further, here is an image shot outdoors at ISO 100.  Notice how sharp and clear the picture is.

This is an example of digital grain or digital noise in a picture taken with an ISO of 1600.  If you look in the shadows, particularly on the right half of the picture, you’ll see a lot of different flecks of color.  This is the “noise” and generally considered an undesirable characteristic in photos… unless of course it’s done for artistic purposes… which was not the case here.  😉 


Next week we’re going to get into the specifics of putting it all together and learning to shoot manual, but for this week we’d like you to take some time to play around and get comfortable changing your ISO speeds.  Go ahead and venture into manual (M) mode and see how it all works together.  It may be challenging, but feel free to post questions and pictures with any problems you’re having.  

Remember, it’s all about light.  In a low light situation, the higher your ISO, the greater (or wider) your aperture will usually be and the lower your shutter speed.  All of these are allowing your camera to let in the most light possible.  In bright lighting situations, the lower your ISO will be.  In bright lighting you can also choose to close down your aperture and increase your shutter speed.  These three components all work together to allow you the most control over your image. 

For a little guidance, and since we’re all stuck inside this time of year, put your camera in M mode and choose the lowest aperture you can on your lens.  Set your shutter speed at 1/60 and now choose your ISO setting – start with ISO 800 and take a picture.  Now change the ISO to 1600 and see how it affects the light and quality of your picture.

Good luck, and we’re here if you need anything!


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