ISO – A practical description for beginning photographers

As I’ve mentioned in my other tutorials, there are three basic fundamentals to exposure. The first two, aperture and shutter speed, have already been covered.  They primarily influence depth of field and sense of movement, respectively.  ISO is the last piece of the puzzle, and we’re going to spend a few paragraphs going through this with enough detail to understand the basics but not enough detail to bore you to death!

So first things first – what is ISO?  ISO was a way that they used in the film days to denote the speed of a given color negative film.  Okay….but that still doesn’t give me anything.  What is it?

I define ISO as your camera’s sensitivity to light.  That’s it.  For a given ISO setting, your camera will alter it’s sensitivity to the light that’s available.  Now that’s something we can get our head around.  Let’s say an ISO setting of 100 is “normal.”  You would use this in an outdoor setting.  An ISO setting of 800 effectively makes your camera more sensitive to light.  So you would use ISO 800 if you were shooting indoors at a party or in a museum.  ISO 1600 would be used in even darker environments, because it makes your camera even more sensitive to the available light.  I use 1600 ISO in a dark setting; inside a medieval church for instance.  Below you see a quick sampling of 6 images that I took. The exposure is noted – I shot these in Manual mode so that when I adjusted the ISO value the aperture and shutter speed stayed constant.

As the ISO in the above images was decreased, the sensitivity to light is also decreased and as a result the exposure gets darker.  Taken at ISO 100, the image is almost black.  I chose the ISO increments above because the math is simple and straightforward.  ISO 200 is twice as sensitive to light as ISO 100.  ISO 400 is twice as sensitive to light as ISO 200.  I think you get the picture…

I tend to view ISO as an enabler for the rest of the exposure.  What do I mean by that?When I capture an image I think more about my aperture and shutter speed settings, rather than my ISO.  I then use the ISO setting to allow me to achieve the desired aperture and/or shutter speed.  This gives me more creative control.  Let’s face it – ISO is pretty boring.  It’s more useful to use aperture and shutter speed to give your images that creative edge.  For example, many people will use ISO to ensure they don’t suffer from camera shake.

Now – ISO has an important property that can have an impact on the image quality.  That is noise.  Noise in a photo is the result of the camera’s sensitivity being set too high and the camera’s sensor is basically not able to cope.  So you get these little speckles in the photo, that tend to be more prevalent in the dark or shadow areas of the image.  This is a massive, massive challenge for many cameras, and camera manufacturers do their utmost to reduce this “noise” in their cameras.  Photographers pay a lot of money for cameras that have “High ISO performance.”

I took some pictures below to show you noise in images.  But to be honest after reviewing these I’m not sure it will get the point across.  These were taken with a 5D Mark III and it’s well known for having low levels of noise at high ISO’s.  Nevertheless you can have a look and do a comparison for yourself – if you click on the image it will give you a larger version.

To give you a final example of noise in an image I cropped the ISO 25600 image even closer and here you can definitely see the “freckles” associated with noise.

Now noise isn’t always a bad thing.  I’ve used it to good effect in some images; it can give an older look to a photo and the grain can add interest, particularly to B&W photos.  Many software programs like Lightroom, Photoshop and Aperture all have the ability to reduce noise in images.  For any given camera a low ISO will always give you best image quality.  All things being equal, shoot at ISO 100 (or 50 if your camera has it).

I tend to shoot using Auto ISO.  This is a setting that some cameras have that allows you to just go out and shoot in Av or Tv mode (Aperture or Shutter priority) and then the ISO auto-adjusts to ensure that the exposure will be correct and that the shutter speed will be fast enough to mitigate blur.  I can use Auto ISO now because I’m very pleased with the quality of images up to ISO 1600; with my 50D I could begin to see image degradation around ISO 800.

Since ISO increases your camera’s sensitivity to light, it invariably will have an impact on your flash strength as well.  So for a given image where you need a stronger flash, instead of increasing the power of your flash you can bump your ISO by an interval or two.

The table below summarizes some of the things we’ve discussed and is a reference for general use.

ISO Setting Shooting Situation
100-200 Outdoors, well lit environment
400-800 Cloudy day, indoor shooting
800-1600 Indoor low light environments, dusk
1600+ Dark shooting conditions

When we get to the section on Manual exposure I’ll get into far more detail on how I use all three aspects of exposure – Aperture, Shutter Speed, and ISO – to create images that will separate your photos from the norm.

8 Responses to ISO – A practical description for beginning photographers

  1. Thank you so much for these tutorials! I’m learning a lot. :D

  2. Rodrigo says:

    Hey Aaron.
    Thanks for your tutorials, they really helped me understanding a bit more about the way cameras work.

  3. Rafael says:

    Very nice explanation on ISO.

    And indeed, good word, the ISO is an enabler, even more with the current sensors’ technology that go up to ISO 6400 without much effort and giving me a flexibility that I didn’t have with my old 2007’s Nikon D40. Actually, the noise itself doesn’t bother me much – what bothers the most for me in the high ISOs is the loss of color depth (images look rather bland) and to some extent, the sharpness (the edges get too blurry).
    I don’t worry much with noise (my images usually have very low noise reduction in LR) – even when sometimes I shoot at ISO 3200 (I currently use a Nikon D7000) or 6400. The D7000’s sensor allows up to ISO 12800, but I never go up there, I think it is a bit over to the edge already and the loss of definition and color is sharp. But in those cases you can’t miss the shot, it is there. :)

    Nice article.


    • Aaron says:

      Thanks Rafael – I’m now shooting with a 5d mark III and the ISO is really good, but I still notice the noise on occasion; I think I may have a sharp eye for noise because many people say that they can use ISO 6400 images but for me even on my 5d Mark 3 it’s just not good enough.

      • Rafael says:

        Hi, Aaron,

        I agree with you.
        Images on ISO 6400 is not THAT good on the 5D Mk.III. I’ve been reading through several reviews of camera models at and on a per-comparison basis, the Nikon D600 has a much better resolving power at ISO 6400. But doesn’t go much beyond this, as 12800 is still “useable”, but the artifacts are already very present.

        All in all, on a technical view of things, the Nikon sensors are lately having the edge in regards of ISO capabilities, this trend started with the D3s, went along with the D700, then came the D7000 (although being a DX crop sensor, it features very good dynamic range and ISO capability). Now the next-gen full frames (D800, D4, D600) are again on the top. Check this out, it is interesting:

        (RAW sample comparisons, between D600, D800, Sony A99, Canon 5D MkIII):

        Check the ISO 6400 samples provided – the Nikon D600 gives the “cleanest” image of the gang, even on the dark areas.
        Although I currently own Nikon gear, I always try to read Canon news, it is always good to have a perspective on both sides before choosing my next camera – which probably will be the D600 by the end of 2013.

        Nice to have technical conversation.

  4. Rhama says:

    OH my holly God. I didn’t know you have a blog. I follow Drica’s blog from years and never knew you had a blog too. Well, your blog seems to be very useful and I will definitely keep your blog in my favorites!! I don’t have a good camera yet and had always taken pictures from AUTO mode but I am looking forward for a new year resolution. (NEW CAMERA) hehehehe…. I always wonder how to take good pictures from a different angle and maybe your tips might help me to get there. Well, I wish to you and Dri a lovely new year specially now with a new baby coming. Best wishes from Rhama.

    • Aaron says:

      Thanks very much Rhama! I’m glad that you found my blog, believe me it’s nowhere near as popular as Adriana’s but one of my 100 hundred new year’s resolutions is to work on it more in 2013! So come back for some more tutorials and general advice on photography, I hope you enjoy taking pictures in 2013!

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