Friday, June 20, 2014

Photography Tip #4 - The exposure triangle for available light photography

Ashley Morgan, one of the new Alices to grace the MTP
ISO 1000, f/2.8 at 1/320th second
For several years, I was the photographer who relied on the automatic modes to help me properly expose an image. Scratch that, I relied solely on Aperture Priority mode for all shooting conditions. It wasn't until I decided to get serious about sports and concert photography did I realize I was severely limiting my ability capture decent photos. In a previous post, I discussed how important it was to have the appropriate shutter speed to stop motion. There are multiple ways to properly expose an image and depending on your shooting conditions certain settings are more appropriate than others. In this post, I want to help you use a base line reading from your automatic modes to get you to the settings necessary to capture the image you need in Manual mode.

The wonderful Dani Kerry as Alice - shot at ISO 1000,
f/4, 1/250th second 
The exposure triangle consists of 3 separate and controllable features in your camera: Shutter Speed, ISO, and Aperture. The chart below breaks down each individual component of the triangle by one stop. Strangely, I believe wikipedia describes a stop in the most appropriate way: "stops are...unit[s] used to quantify ratios of light or exposure, with each added stop meaning a factor of two, and each subtracted stop meaning a factor of one-half". Each jump to right in the chart below means you gather twice as much light, while a move to the left means you gather half as much light. 

Shutter Speed
Freezes motion & gathers less light -----------------------> Introduces motion/blur & gathers more light 

ISO (sensitivity of camera sensor to light)
Clean images & gathers less light ----------------------------------> Grainier images & gathers more light

Greater depth of field & gathers less light  -------------> Shallower depth of field & gathers more light

The talented Johnny Gomez as Dormouse - ISO1000, f/2.8 at 1/250th second

I personally operate best using examples, so I figure I will start with one. Let's say you're at the Mad T Party out in Disney's California Adventure and the auto mode tells you that you need the following settings to capture the amazing Alice rock out on stage: ISO 800, shutter speed of 1/125th and an aperture of f/4. We know from my last post, Know Thy Shutter Speed, we need a shutter speed of 1/250th or greater to freeze an artist in motion.  Let's assume you want to play it safe and use 1/500th of a second.  If all things are equal and you ONLY change your shutter speed, you will be 2 stops underexposed (two jumps to the left on the shutter speed chart). In order to compensate for this shift in exposure, you will have to move either your ISO and/or aperture two stops to the right (if we are using the chart above as a guideline). The following are examples that will give you the same exposure but will yield different photographic qualities.   

Mixing things up with a little 80z All Starz. ISO 400, f/4 at 1/250th second

Original Exposure
ISO Only - 2 stops
Aperture Only – 2 stops
Aperture & ISO – 1 stop each
Shutter Speed

ISO Only - 2 Stops
If you look at the chart above, you will notice as the ISO increases, the more digital noise you will add to your photograph. The pixel density and the quality of your camera's sensor will determine how much grain or artifacts you will introduce. Get to know your camera and see how much of this you are willing to tolerate. As for me and my Olympus E-M1, I try not to push it past ISO1600, but will bump my ISO to 6400 in a pinch. This first option to balance my exposure is not what I typically do.

Opening up my aperture by 2 stops is what I normally do depending on my shooting conditions and if I plan on photographing one person.  Part of the reason why I like shooting with primes, besides being relatively sharper than zooms, is that I can gather significantly more light and having the option to throw my background into blur (the bokehlicious effect). Wider apertures (or smaller f stops) are great for subject isolation but the moment you photograph groups that are staggered or move outside the focal plane of your primary subject you will run into problems as your depth of field may be too shallow. 

Notice the staggered position. I would need a greater depth of field to have both
artist in focus. Opening up my aperture would not be ideal - ISO 400, f/4 at 1/250th second

APERTURE & ISO - 1 stop each
This will probably the route I will choose 9 times out of 10.  Not only do most zooms have the capability to shoot at this aperture, but it provides a great balance for most situations with regards to depth of field, digital noise and speed. An f-stop of f/2.8 typically has enough depth of field to cover groups, especially with cropped sensor cameras and most modern digital SLRS and mirrorless cameras produce clean photographs at this ISO range.

Not to say there is anything wrong with this particular exposure, but in the case of concert photography, I would hardly ever shoot with a shutter speed of 1/125th or slower. The only time I could ever think of a situation where this is fast enough for a concert is during a ballad. Outside of concerts, I would consider this a usable shutter speed for non-moving portraits. In fact, I have used 1/6th for posed shots (this is where the Olympus 5-axis image stabilization has really impressed me). 

ISO 500, f/2 at 1/400th second
In my opinion, the exposure triangle is one of the most basic principles of photography that is often times overlooked. The digital age has made it so easy for us to just pick up a camera and take a decent photograph. Modern cameras are smart enough to know how to properly expose for almost any scene, but it is not as intelligent as our brains to analyze and read changing conditions and varying subject matters. It will never know that it needs to speed up the shutter speed to effectively freeze a band running around the stage or to close up the aperture to get an entire group in focus. Don't get me wrong, I rely on the auto modes in my camera to help me get a baseline, but then I defer to my knowledge of the exposure triangle to get the image I want. Next time you're at a concert, try shooting manually even for one set. You might surprise yourself at how many more keepers you'll get.

So say we all,