Friday, April 10, 2009

Friday's Photo Tip - What is ISO?

Friday's Photo Tip - What is ISO?

texture of ripples in wet sand

Dory, over at Can't Remember Diddly, left a comment on last week's photo tip, and she stated:

"When your reader used the numbers 200 and 1600, it made me think that they are confusing shutter speed and ISO".

I will have to admit that I was thinking along the ISO lines too with the numbers that were given, so I thought it would make a good topic for this week.

Just what exactly is ISO, you ask?

Well technically, the letters stand for International Organization for Standardization. They are the standards that define the speeds for film.

It uses an arithmetic and a logarithmic scale to make this calculation, and we recognize it as ISO 100, 200, 400, etc.

Not very interesting a topic so far, but it really is a necessary part of understanding your camera.

Think of it like this - a camera is used for capturing light.

How much light is available for it to capture affects many settings in your camera.

In the days of film, it was important to know your lighting conditions before hand,so you could buy the appropriate film speed. With today's digital cameras, that "film speed" or ISO can be flipped back and forth without a problem.

An ISO of 100 is a fairly "slow" film, which means it needs more light to capture an image. A bright sunny day, or a studio filled with flood lights would be great for this less sensitive ISO setting.

An ISO of 1000 or 1600 is a "fast" speed which is more sensitive to light and can pick up lower light levels - a church or a candle light dinner.

Now, there are always pros and cons to everything, and I will give a few of these for the different ISO settings.

In the film days, a photographer's first choice for ISO was always a lower number - 64 or 100 was about as far as one wanted to go.

The lower the number, the sharper and clearer the image, especially if larger sized prints were going to be made.

One would sacrifice sharpness for graininess as the ISO number began to rise. Grainy photos were the norm for high ISO images.

So, now that we use digital cameras and not film, you would think that we no longer have to worry about this graininess any longer.

Digital has introduced us to something else that we have to worry about with ISO.

Once again, the lower the number the better.

Digital Noise is a problem that begins to creep into an image when a higher ISO is used.

Noise is very undesirable - especially if a larger image is going to be printed.

The digital sensors in the cameras tend to "heat up" as they process images, and the higher ISO settings make them work harder - making more heat.

Heat is one of the reasons for the "noise". Longer shutter speeds, hot days, and prolonged use of the camera also create "noise".

In film, the graininess is spread evenly across the entire image.

With digital, the noise appears as splotches or spots or an overall blurriness, sometimes only showing up in certain shadows or colors in the photo.

The larger the sensor in the camera, the better it is able to handle the noise. DSLRs deliver a less noisy image at high ISO settings than the smaller point and shoot cameras.

The texture in the image above contains noise. Due to the lower light levels, I used a higher ISO when taking the photo.


  1. Hi KML- I just wanted to say I love your Friday Photo tips! There simple, to the point and explained perfectly...good job. I'm new at photography and am still learning and I find your tips "clicking" in my head so well and staying with me, thank you! =)


  2. Great post. Definitely helped me to understand ISO.

  3. Thanks, Elsie - glad they can help!

    If you have any questions, be sure to let me know!


  4. Kathy excellent post, I like it. You know sometimes with grainyness I get some nice effects, and sometimes it sucks because I thought I had the moment, lol. Yes heating up is a big issue, but the amazing things is that the technology always is moving forward, and I bet they will come up with the solution one way or the other. Thanks for the great post, take care and have a good Easter. Anna :)

  5. I've been wondering about this stuff for a long time now. I try to learn a little more as I go, and this was a nice step forward. Thanks.

  6. Kathy, thanks for the interesting and informative post. Sometimes we forget to be mindful of noise, and end up with bad shots. I've done many existing light shots with insufficient ambient light, and ended up with noise in the darker areas especially.

    I find it hard to distinguish noise in shots of sand!

  7. Really awesome blog. I enjoyed reading this review from you. I found that you really update your site regularly that made me more interesting. I've bookmarked your site for my future use.

    Thank you

  8. Interesting info. Since I started using digital, I don't even think about such things anymore, so it's good to get a review now and then.

  9. I almost had a heart attack when this post came up in my reader and mentioned me! LOL

    This was a fabulous explanation for ISO... well done! You rawk!

  10. Thanks for the instuctional post. Helps me a lot.

  11. What a good, straightforward explanation. I had a hard time adjusting to higher ISOs when I first switched from film to a DSLR. I was accustomed to shooting ISO 50 (Fuji Velvia) or 64 (Kodachrome), and only occasionally a 100 ISO film. Now, with the digital camera, I shoot mostly 100 and ABOVE (depending...). A whole new world for me.

  12. Very cool way of explaining ISO, ISO is a very important component of night time photography, the trick is to use just enough but not so much that your pics are grainy with all the amplification.


Thanks for taking the time to leave a comment - it is appreciated! I will do my best to return it with a visit to your blog. Take care, and enjoy!


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