Photography Tip #6: ISO

The ISO setting on your camera is a measure of how sensitive your camera sensor is to light.  In the days of film (Okay, I know. I know. Film is still very much around.) you would see the ISO number indicated on a roll of film listed as the film speed.  With film you were stuck with that ISO setting until you finished the roll of film.  On your digital cameras today you scan switch ISO settings with each image you take. This gives you great creative freedom.  You can choose from ISO 100, 200, 400, 800, 1600, and even higher within any given shoot.  But what do these numbers mean?

It's actually very simple. A low ISO (100) is not very sensitive to light.  A high ISO (1600), on the other hand, will be very sensitive to light, so you can take pictures without flash in much dimmer settings than you could at the lower ISOs.  

To make this crystal clear, it's time for yet another analogy from Bryan Peterson's book Understanding Exposure. (You really should run out NOW and get a copy for yourself.  It's super user-friendly.  Besides, I'm thinking he should probably give me some kind of kick-back for how often I refer his book, right?)  Anyway, Bryan Peterson uses the analogy of worker bees to explain how ISO settings affect your images.  

Imagine you have 100 worker bees on hand to gather the light in an image and deliver it to your camera's sensor.  Those would be some speedy worker bees, right?  Well, now imagine you have 200 worker bees to gather the same amount of light.  It would take those bees half as long to gather the needed light as the 100 bees took.  400 bees would gather the light 4 times as fast.  800 bees would gather the light 8 times as fast.  You get the picture.  So, each time you double your ISO setting you can halve the shutter speed.  So, you will be able to use a faster shutter speed in low light.  This is probably the most important aspect of ISO.

How does this affect your photography?  Let's say your aperture is set as low as your lens will allow at f/1.4.  Unfortunately, you forgot your tripod at home, so you are limited at how low you can set the shutter speed (since you will be hand-holding the camera).  You won't be able to set the shutter speed as low as your camera's light meter suggests in order to get a proper exposure when you are in a dimly lit room.  

How can you get more light onto the sensor so that you can shoot at a higher shutter speed and forego the tripod? Simply increase your ISO settings on your camera.  If it is set at ISO 100, try ISO 200 first.  If you still need a faster shutter speed, try ISO 400.  Continue adjusting the ISO settings until you reach a fast enough shutter speed to shoot without a tripod.  It goes without saying that each time you adjust your ISO settings you will also have to adjust your shutter speed until your camera's light meter indicates a proper exposure.

(Not sure what a light meter is?  Grab the manual that came with your camera and figure this out fast!  Understanding your light meter is crucial to learning how to shoot manually.)

You should also know that colors will be most saturated and images will be sharpest at the lower ISO settings.  In most cameras you will also see increased "noise" or graininess in images where higher ISO settings are used.  For this reason, since I shoot using available light, I always try to shoot in conditions that allow for an ISO setting of 100.

How do you know what the slowest shutter speed is that you can shoot your particular lens at without having to use a tripod?  That's pretty simple as well.  Generally speaking (unless you have a VERY steady hand) your shutter speed should not fall below the lowest mm reading on your lens.  For example, if I am shooting with my 50 mm lens, I should try not to shoot without a tripod if the shutter speed is lower than 1/60th of a second.  Shutter speeds faster than that should result in images that are pretty clear when hand-held.  If you are using a 24-70 mm lens, you should not shoot slower than 1/25th of a second without a tripod.  If you are using an 85 mm lens, your lowest shutter speed should be 1/100th of a second.  Anything slower than that requires a tripod.

So far we have learned about Shutter Speed, Aperture, and ISO settings. Together these three make up what Bryan Peterson (there's that name again) refers to as The Photographic Triangle.  Simply put, a correct exposure is a simple combination of these three factors.  

But what is a correct exposure?  That all depends on the desired result. Do you want to freeze the action, then place priority on a fast shutter speed and adjust your ISO and aperture settings until your camera's light meter indicates a correct exposure.  Do you want to record the tail lights on passing cars as a blurry streak of red and yellow? Then, place priority on a slow shutter speed.  Do you want to isolate one candle on top of a birthday cake?  Then, place priority on a large aperture (small f-stop) adjusting your shutter speed and ISO settings afterward to indicate a correct exposure. 

Any number of combinations of ISO, Shutter Speed, and Aperture can result in a correct exposure.  Only one of those (usually about six or seven different options) combinations is what Bryan Peterson refers to as The Creatively Correct Exposure.  And that, my friends, depends upon you - the creative force behind the lens.

Here are some general guidelines about which ISO setting to use:

Outdoors in brightly lit sunlight - ISO 100

Outdoors but in overcast light - ISO 100 or ISO 200

Shooting indoors without flash - ISO 100 if possible, use higher ISOs when needed

One last note:  When adjusting your ISO settings, always remember to change it back to ISO 100 at the end of the shoot - unless, of course, you are purposefully trying to increase the grain in your image for artistic affect.  Just remember, the preferred ISO for highest sharpness, color saturation, and image clarity is ISO 100.  That should be the starting point for every shoot.

Photography Tip #3: Aperture

The aperture is an adjustable opening found inside the lens used to regulate the amount of light passing through the lens and onto the film (or digital media).  Apertures are measured as f-stops.  A large f-stop (f/11, f/16, f/22, etc.) indicates a small aperture.  Small f-stops (f/1.4, f/2.8, f/5.6, etc.) indicate a large aperture.

While aperture can be used to manipulate the amount of light you allow into your camera, it is better known for its ability to manipulate depth of field (the area of sharpness from near to far within a photograph).  

If you want everything in your picture to be tack sharp (from the flowers lining the fence in the foreground to the chimney on the farmhouse in the distance), then you need to select a smaller aperture (anywhere between f/16 - f/22 or greater).  

In contrast, if you only want a small amount of your image to be in focus (you want to focus in on just one red rose from your grandma's entire rose garden), then you will want to use a larger aperture (anywhere between f/1.4 - f/5.6).  The smaller f-stop will blur the background while keeping your subject in focus.  This helps to isolate your subject and bring more attention to it (as in this image below):

In his book Understanding Exposure, Brian Peterson explains aperture like this: 

"Imagine using a funnel with a very small opening and pouring a one-gallon can of paint through it into an empty bucket.  Compare this process to pouring a one-gallon can of paint into the same empty bucket without the aid of a funnel.  Without the funnel, the paint gets into the bucket quicker, but it also splatters up on the bucket sides, as well.  With a funnel, the transfer of paint into the bucket is cleaner and more contained.  Keeping this is mind, you can see that when light is allowed to pass through small openings in a lens, a larger area of sharpness and detail always results."

In the image above, I used a very large aperture - which in essence allowed the light to splatter along the sides of the paint bucket.  So, only the area focused on (the red flower) is sharp.  The out-of-focus blurry background is the remainder of light that was allowed to splatter up along the sides of the bucket.  Had I taken this image with a very small aperture (f/22), then every leaf in the background would have been tack sharp.

So what aperture do you choose?  It all depends on the end result you desire.  If you want to see every tiny detail from front to back, choose a very small aperture (large f-stop).  Get out your funnel.  If you want to limit the area of focus to a single area within a larger composition, you will want to purposefully blur most of the other details in your image by choosing a very large aperture (a very small f-stop).  Pour the light in and let it splatter!

I don't know about you, but I'm a visual learner and have always learned best by seeing concepts in person.  So, to illustrate what happens when you adjust your aperture, I've included the following three images:

In the first image, you'll notice that very few of the rows of beads are in focus.  At f/1.4 (a very large aperture) most of the light was allowed to splatter away from the central area of sharpness creating an image that is mostly out-of-focus.

In the second image I used a medium aperture of f/5.6 to create a somewhat sharper image.  But, because it is still a lower f-stop, you still see some fall-off on the outer edges of the image.  You could say I used a funnel here - just a very large one.

The last image was taken at f/22.  You'll notice that every bead is tack sharp.  With this tiny aperture (large f-stop), all of the light was contained leaving nothing to splatter onto the edges.  As a result every bead is tack sharp.  If you look closely, you will even notice that the bookshelves behind the bead board also came into greater focus at this aperture.

If you are really paying attention, you will also notice that all three images appear equally bright.  To achieve the same exposure for each image I had to remember to adjust the shutter speed or the ISO settings each time I made an adjustment to my aperture.  Had I not done that, the image would get darker each time I switched to a smaller aperture.  

Confused?  Think about it this way.  If the aperture is the size of the hole inside your lens where light enters the camera, doesn't it make sense that less light would be entering the camera if the size of that hole is shrinking?  So, how do you get more light into the camera?  Simply make sure that hole stays open longer.  And that in a nut-shell is why I must change the shutter speed to ensure a proper exposure.  

Last time we learned about shutter speed (timing).  Can you see now how it is all coming together? This photography stuff isn't as daunting as you thought, now, is it?

There's just one last thing to discuss when it comes to aperture and depth of field.  When using a large aperture (a small f-stop), it is important to remember to keep your subjects on the same plane when taking group pictures.  If one person is further in front of another, one will be in focus and the other one will be out of focus (one will be right under the funnel and the other will be splattered up against the side of the bucket).  Similarly, if one is taller than the other (and I've focused in on the taller of the two), the shorter one may not be in focus because he is on a different plane.  

In cases like this you may want to go with a smaller aperture (a larger f-stop) to insure that everyone of importance remains in focus.  When taking group pictures, another good tip is to tell your subjects to imagine their noses are all touching the same pane of glass.  This will help to keep them all on the same plane - and in focus.  Sitting them at a table or on a couch also helps to keep them in the same plane of focus.

The following two pictures illustrate this well:

In this first image, the boy and the ball are almost on the same plane, so both are pretty much equally in focus.  If you look closely, though, you will notice that the ball is not quite as sharp as the boy.  This is because the ball is on a slightly lower plane than the boy's face (which was the focus point for this image).  

Keep in mind that this is the nature of a large aperture.  It lends itself to a very shallow depth of field.  When using a small f-stop it is not uncommon to have one eye in focus and the other blurry.  To make the portrait appear sharp, remember to focus in on the eye closest to the camera.  It also helps to shoot straight into your subject's eyes (not looking down on or up to) and to step back a little.  The closer you are to your subject, the less of the image will be in focus.

In the last image, the ball is in front of the boy, and the boy is set further back.  The boy falls out of the plane of focus and is blurred as a result. Using a low f-stop is the trick to isolating the ball from the boy - which can be a really cool affect.  It's how you can make a lone flower stand out amidst a whole bed of roses.  It's how you can focus in on just one child's face in a crowd of many other children.  It's how you can avoid a distracting background from overwhelming your subject.  In short, it's a photographer's best friend. 

Having a good understanding of aperture and shutter speed separates the beginners from the pros.  It takes a lot of practice, though, so grab your cameras, and get out there!  The fun is just beginning.