What is ISO?

It is the number that describes how much the processor amplifies the light collected by the sensor.  A higher number means the processor works harder to produce a correctly exposed image.

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Each step on the ISO scale doubles or halves the cameras sensitivity.  For example, if you change your ISO from 200 to 400 the camera becomes twice as sensitive to the light that hits the sensor.

So why wouldn’t you want your camera to be as sensitive to the light as possible?  Some undesirable effects happen when you raise your ISO too high.  Colors become less saturated and noise increases.

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Look at how much smoother the first picture is at low ISO.  In the second picture with a high ISO, you can see (especially in the background),  tiny dots (noise) and the lack of vibrancy.


Lets take a look at what is happening when you raise the ISO

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Sensor size, processor, and mega pixel count will have an effect on the amount of noise you see at high ISO’s.

I took this Photograph with 3 different Nikon cameras at 3200 ISO

  1. Point and shoot Nikon A900
  2. Full frame Nikon D810
  3. Full frame Nikon DF

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Here are the cropped images

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Nikon A900 – Point and Shoot – 20 megapixels

You can see in the point and shoot camera there is a lot of noise at 3200 and the image looks almost like a painting instead of a photograph.  This has a lot to do with the fact that the sensor in the camera is very small.

 

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Nikon D810 – Full Frame – 36 megapixels

The Nikon D810 is a full frame camera which means that the sensor is 5.6x larger than the Nikon point and shoot.  You can see that the the image looks much better than the point and shoot even though you can still see some noise.

 

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Nikon DF – Full Frame – 16 megapixels

The Nikon DF is also a full frame camera but it has far less megapixels than the D810.
With less pixels, each pixel on the sensor is physically larger and performs better at gathering light.

Just for fun, let’s look at the D810 and the DF at ISO 12800:

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The D810 looks much noisier and the DF is still a usable image.


 

High ISO’s can be very useful if you are in a low light situation, but you really want to stay as low as you possibly can.

  • Use a tripod with a longer shutter speed
  • Open your lens aperture to let in more light

Experiment with your camera to see what the highest ISO is that you are comfortable using.

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All text and images by Melinda Walsh

www.mlnda.com


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