Aperture, Shutter Speed and ISO

June 26, 2012  •  5 Comments

So in my first proper blog entry I’m going to cover the fundamental point of all photography. How to capture light and the interplay between Aperture (the opening in the lens) and shutter speed (the length of time the sensor is exposed to light).

The best way to think of light is as a stream of water; if you collect it, it accumulates.  So a photograph is like a bucket, filled with light or in our case water.  Your camera is like your garden hose and tap, or more specifically the camera’s aperture is like the pipe of the garden hose and the shutter is like the tap.  To create a complete well exposed photograph, the bucket must always be filled.  Underfill the bucket and the photo is just black (Underexposed).  Overfill the bucket and the photo is blown out and white (Overexposed).

So if we look at my drawing, on the left we have 3 scenarios with a pipe, a tap and a bucket.  In the first instance the pipe is of average width, or aperture, say f7.1, so to fill the bucket we need to turn the tap on until its full which for arguments sake let’s say it takes 1/50 of a second (shutter speed). 

Now what happens if we narrow the pipe, to say f22 (the smallest aperture possible)? Naturally it will take a lot longer to fill the bucket, as 1/50 will only allow a tiny bit of water in.  So we must leave the tap on for longer, say 2 or 3 seconds.  So we see that narrowing the aperture, (increasing the f-number) means that the shutter speed needs to become longer in order to compensate. 

So if we widen the pipe to f2.8 (large aperture) we can fill the bucket really quickly, say 1/1000 of a second on the tap.  This is why people refer to wide aperture lenses eg. 70-200mm f2.8 as being “fast”. They allow for fast shutter speeds, freezing motion because they let a lot of light into the camera in a very short space of time.

 

This relationship explains why sports photographers have these massive lenses and why landscape photographers carry tripods around with them all the time.  Landscape photographs require small apertures – I’ll cover this soon – and because of this they produces long shutter speeds so the tripod stops them getting camera shake.

 

Finally we come to ISO.  ISO is the sensitivity of the sensor in the camera, and to fit in with our pipe and tap analogy, we can view ISO as being the size of the bucket (my drawing on the right).  A large bucket (low ISO) takes a long time to fill up, whereas a tiny shot glass (ISO 3200) will take a tiny amount of time to fill.  However, we’re thirsty for photographs so a good amount of water is always better quality! Try and shoot at as low an ISO as you can, so that your photos aren’t grainy.

Let’s use an example.  You’re taking a photo of your friend on a bike, but it’s blurred.  You need a wide aperture (the smallest f-number you can get) this will allow you to also achieve the fastest shutter speed you can.  Still blurred?  Ramp the ISO up from 100, try 400 or 800.  This will allow you to have an even faster shutter speed.

Zak Holmes When taking this photograph of Zak on his mountain bike, he was travelling fast, so I needed to have a fast shutter speed.  I set my camera to ISO 400 and my aperture to f4 to ensure my shutter speed would be fast.  It did the trick and my shutter speed was 1/2500 of a second, meaning I stopped the motion, other than the dust coming off the jump!!

 

When taking this photograph of the Fairy Pools on Skye in Scotland, I wanted to show the movement in the water flowing through the pools so I used a small aperture, f18, in order to create a longer shutter speed of 1/2 a second.  This allows the viewer to know isntantly that there is motion in the scene, even though it's a photograph!  I had to use a tripod for this shot so I dropped the ISO to 100 as camera shake wasn't going to be a problem.  All these settings result in me having as high a quality photograph as I could.

 

I hope this blog entry has helped you understand the relationship between aperture and shutter speed, and how ISO can help you out.  If it did help you, then please share it with your friends, via twitter or facebook.  If you have any questions please get in touch using the comments section or drop me an email at Blog@DruDodd.com

 

Best wishes,

Dru

www.facebook.com/drudoddphotography


Comments

Mark Hannah(non-registered)
Wow!! So well explained even i understand now!! Off to try and get a good, well lit picture of a hose and bucket!
Keep up the hard work, as much as i joke, its inspirational....
Linzi B(non-registered)
This is something i really wanna crack,
so thanks for explaining it so well.
Makes a lot more sense to me now!!
Philip Whittaker(non-registered)
Nice way of explaining it mate, with great shots to back it up :)
Alexander Wilson(non-registered)
Well explained! Looking forward to more!
Richard Heathcote(non-registered)
Beautifully explained Dru.
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