Shutter Speed

In our quest to understand the basic variable settings of a camera we’ve so far covered ISO and Aperture. Today we’ll cover Shutter Speed.  Next week will be Focal Length followed by Focal Distance.  Once we’ve covered these five variables and have a basic concept of what they are and how we adjust them, then we can use these variables to create all kinds of exciting compositions.  Hang with me a few more weeks and we’ll start putting all this together.

A shutter is nothing more than a device to let light in and out.  On a pinhole camera described last week, a basic wooden box with a pin hole for a lens, you finger becomes the shutter as you move it over the hole, and away from the hole.  More recently we had 100% mechanical shutters.  When I say 100% mechanical, I’m talking about not only the physical part that moves to let light in and out, but also the device part that sets the speed and timing of it moving in and out.

shutter

In film SLRs we traditionally had leaf shutters.  The “leafs” were most often made of a dark fabric, but could also be made from strips of stainless steel and other special metals.  Remember putting film in your 35mm SLR?  The full spool went to the left side, you pulled out a strip of film and then fed it through the take up reel on the right side?  In the middle, that rectangular black thing you laid the film over?  That was a leaf shutter with a fabric curtain.  The curtain merely moves horizontally from side to side.  Watching the curtain move in real time is interesting, it looks like a piece of fabric very quickly slides from left to right.

Inside 35mm SLR

Today’s cheapest compact point and shoots sometimes have 100% electronic shutters.  All these do is turn the sensor on and off for the desired time/speed.  These work with our camera phones and cheaper P&S’s, but function and image quality suffers in ways obvious to a more advanced level of photography, but not so obvious to the casual user.

Modern digital SLRs (DSLRs) have combination mechanical/electronic shutters.  The mechanical parts are the steel leaf blades that move up/down like a window shutter, and the electronic part is what controls the timing of how long the shutter remains open.  These shutters are modern marvels.  On the professional cameras like the Nikon D3 and Canon 1D series, the shutters are rated for at least 150,000 actuations.  This would last an amateur a life time.  They also move at up to 11 frames per second which is lightening fast for a mechanical mechanism.  These are some really tough and special shutter mechanisms.  Below, are the shutter assembles for the Nikon D3 and Canon 1dsMarkII respectively.

Nikon D3 shutter assemble  Canon 1dsMarkII shutter assemble

How long we leave the shutter open affects exposure.  The longer we leave it open, the more light hits and is gathered by the sensor.  Also, the longer we leave it open, the more chance we’ll get “camera shake” resulting in a blurred image.  When we open and close the shutter very fast, it allows us to freeze objects like balls in the air, butterfly wings, and all sorts of sporting events.  Recently in the Olympics a high speed camera was able to verify Michael Phelps won the 100 meter butterfly by a mere 1/100th of a second.  This is way too fast for the human eye to see, and if it wasn’t for the excellent Omega timing system and high speed cameras, the call would have been up to some official and argued about for years and we’d never really know who won.

Jumping soi dog Somchai and a jumping soi dog with high shutter speed

Shutter speed is measured in seconds.  Like aperture, we also talk about shutter speed in “stops.”  Remember, a stop is either double the previous value, or half the previous value.  A shutter speed of 1/1000th reduced one stop is 1/500th.  1/500th reduced two stops is 1/125th.  Reduced four more stops 1/8th.  Once you get in the habit of talking about shutter speed, aperture, and ISO in “stops”, then it becomes very easy to understand how they work in relation to each other, and how when we change one “one stop”, it affects the other “one stop.”  We’ll have plenty of examples of this in future columns.

What shutter speed to use?  It really depends.  It depends on available light, if the subjects are moving, the focal length of the lens, the aperture selected, and the ISO.  The “Basic Rule” and a good starting point, is that shutter speed should be 1/(focal length)  So, a 50mm standard lens should require a 1/50th shutter speed.  A 24mm lens should require a 1/24th shutter speed, and a 300mm lens should require a 1/300th shutter speed.  This is a starting point only, a general rule of thumb.  There are many reasons you’d select a speed either faster or slower, reasons we’ll cover later.  For now, just understand what a shutter is, that the length of time it’s open is measured in seconds or stops, and that if we leave the shutter open too long we’ll get blurred images, and if we open and close it really fast we can freeze action.