Thursday, November 5, 2009

ISO in Photography

So in a previous post I introduced you to the first of the three most important settings on your camera: Shutter Speed.   Now we'll discuss the second:  ISO.

Don't ask me what the initials stand for.  I don't know; and does it really matter?  What matters is what ISO is--a measurement of how quickly your camera’s sensor absorbs light or how sensitive your camera's light sensor is.  A high ISO number (i.e. 400 or 1/400th of a second) makes your camera's light sensor more sensitive and therefore you require less light for picture taking.  In other words, you want a high ISO speed when shooting in dark places without a flash.  A low ISO number (i.e. 50) makes your sensor less sensitive and therefore you require more light for picture taking.  In other words,  you'll want a low ISO speed when shooting outdoors on a sunny day.  ISO speed settings make full use of the available light in the environment in which you are taking the picture.

The problem with ISO speed is that the higher the speed, the more grain you introduce into your picture.  As a general rule of thumb, you want to use the lowest ISO speed possible given the lighting conditions you are in. 

In Mommy terms: Use a high ISO number when shooting in low light so you don't underexpose your picture.  Use a low ISO number for shooting in bright light or sunlight so you don't over expose your picture.

ISO 50 without and with flash
50 is the lowest ISO my camera will go.  Note that you really can't see much in this picture because it was too dark.
 ISO 100 without and with flash 
100 is the next ISO on my camera.  Getting better but still too dark.
  ISO 200 without and with flash
Up another notch is ISO 200.  Now we're getting somewhere (at least when you use the flash)

ISO 400 without and with flash
The highest ISO my camera will go is 400.  Definitely an improvement but still not perfect

I was able to make the ISO speed the ONLY variable in the above pictures by changing my camera to the Program AE mode or P mode on my Cannon camera. 
Your challenge:  set your camera to P mode (or whatever your Program AE mode is on your camera) and play with ISO speeds.  Let me know how it goes!

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Catharine said...

So, when are you putting your pennies away for a new camera? Looks like you are learning a ton and will be wanting one soon!

Maura said...

I am trying to save up for a camera that can do this. I wish there wasn't such a jump in price from point and shoot and DSLR's. Nice tutorial!

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