Food Photography Tutorial (Part 2: Exposure)Posted: November 9, 2011
One of an SLR’s best features over a point+shoot is the ability to have greater control. Control over what? Let’s start with exposure which simply means how dark or bright a picture is captured. A picture that comes out too dark is underexposed while a picture that comes out too bright is overexposed.
We often take exposure for granted because point+shoot cameras automatically expose our pictures for us. As we go through the principles of exposure, you’ll also learn about important composition techniques like freezing motion and creating a shallow depth of field.
An SLR camera enables you to control exposure using three distinct levers - shutter speed, aperture and ISO. Think of exposure as a three-legged see saw. Your goal is to constantly keep the three in equilibrium.
If you plan on shooting in manual or semi-automatic modes like “M”, “Tv” or “Av”, read on…
This is the speed at which the shutter of a camera opens and closes. You can hear it. The shutter of a camera blocks the sensor (i.e. film) from light. When you click to take a picture, the shutter doors open, capture the frame (by allowing light through the shutter doors and onto the sensor) and close.
Think of shutter speed as a knob on a faucet. The longer the shutter doors are open (i.e. longer shutter speed), the more light you are letting. If your shutter speed is open for too long, you will overexpose your picture (i.e. too bright).
Shutter speed is most often measured in fractions of a second. Long shutter speeds are measured in full seconds. Measurement examples include 1/25th of a second, 1/50th of a second, 1/100th of a second. On a Canon, these measurements appear as 25, 50 and 100 inside the viewfinder (instead of 1/25, 1/50, 1/100) even though they’re still technical fractions.
In addition to controlling a picture’s exposure, shutter speed is also a tool used to freeze (or blur) motion. This is less relevant for an immobile subject like food but is an important technique, especially when shooting subjects like kids (who never sit still). Use a fast shutter speed to freeze them (vs. a blurry image). Just remember that by using a fast shutter speed, you are making a sacrifice by taking in less light. This means your photo may be at risk of being underexposed (too dark). You will have to offset by either raising your aperture or ISO to achieve a properly exposed photo (repeat after me…3 legged see-saw…equilibrium).
I illustrate two different applications of shutter speed below. The image on the left has a very fast shutter speed (1/1,600th of a second) which I needed to freeze the fast-moving subject. In capturing this picture, I started by selecting my desired aperture (while cognizant that I needed a FAST shutter speed). I chose 2.8 (the lowest my 24-70 2.8L lens can go) because I wanted a shallow depth of field (blurry city). ISO stays at 100 (ideal) unless I need MORE light for some reason. It was broad daylight so chances of that were slim. I then selected my shutter speed (ss). I had two things on my mind: 1) I need to select a very fast ss to prevent the picture from getting motion blur (different from camera shake) and 2) I need a ss number that will balance my preset aperture and ISO settings. I ended up at 1/1,600th of a second. My suggest to you is to practice. Play around with random shots at different times of day and it will become second nature (like riding a bike?).
Now for the picture on the right where the river stream is blurry but looks different from what your eyes would see. In approaching this picture, I knew I needed a LONG shutter speed to create this effect (where the immobile objects are sharp but moving objects are blurry). I also knew I needed a tripod to avoid camera shake (see rule below). Lucky for me, there was a rock that I could rest my camera on (in lieu of a tripod). I’d normally start with a desired shutter speed except in this case, I knew that I was limited by the amount of light that would let in (probably too much because it was already a bright day setting). The way to balance that excess light is to reduce the aperture considerably (use a higher number). My lens’s aperture only went up to 22, so that was my starting point (small hole…see section below). Again, I left the ISO at 100 because I didn’t need more light (if anything, I needed to find a way to reduce the amount of light). I then backed into my shutter speed (in achieving proper exposure) of 1.3 seconds. That was long enough of a shutter speed to achieve the effect I was going for.
The other consideration when altering shutter speed is an unpleasing effect called camera shake. Your hands are always shaking whether you realize it or not. If your shutter speed is too slow, camera shake will make your entire picture come out blurry. This is different from the effect I achieved above in the woods where only the water was blurry! This is why people use tripods. The rule of thumb: avoid shooting (w/o a tripod) at a shutter speed that is less than the inverse of your focal length. For example, if your lens is set to 55mm, you should not use a shutter speed less than 1/55th of a second (or 55 as displayed in your viewfinder). To complicate matters further, you need to adjust that rule of thumb for what is known as a crop factor. Most entry-level cameras have a 1.6x crop factor, meaning that the adjusted focal length of a 55mm focal length on a camera like a Canon Rebel is 55mm x 1.6 = 88mm. As such, you should really avoid shooting at <1/88th of a second when using a 55mm lens on a Canon Rebel.
camera shake rule of thumb: shutter speed >= 1 / (focal length * 1.6)
I’ll cover the subject of focal length in a future post, but here are the basics for now. Focal length is the ‘zoom’ at which your lens is set for any particular picture. It’s set by the ring around your lens that you turn (there are usually two rings: one for manual focus and another to change focal length).
Shutter speed occurs within the camera body while aperture is specific to the lens that’s attached to the camera. Every lens has what’s called an aperture, or a hole through which light travels. Think of aperture as the width of a sink faucet and shutter speed as the amount of water pressure coming through the sink. There are two ways to speed up the amount of water going through a sink: increase the water pressure or use a wider faucet. Similarly, there are two ways to increase the amount of light in a picture: slow down the shutter speed or increase (i.e. open) the aperture.
Aperture is also known as an F-stop. Examples of aperture are measurements like 2.8, 5.6, 11, and 22. These same measurements are sometimes displayed as F/2.8 (same thing). The lower the number, the bigger the hole, the more ‘open’ the aperture is. A bigger hole allows more light to reach the sensor. The range of aperture numbers is specific to the lens that you are using. Most lenses range from 3.5 to 32 while expensive lenses go down as low as 2.8 and sometimes 1.2.
In addition to controlling a picture’s exposure, aperture is also a tool used to achieve background blur (the effect is known as a shallow depth-of-field and the actual blur is referred to as bokeh). This is extremely important when shooting food. Most appealing or professional looking pictures have shallow depth of fields, which by default creates more attention to the item in focus.
The example below shows two pictures with the exact same exposure (light reading) and composition (set-up). The only difference is their depth of field. The one on the left has a deeper visible plane (i.e. greater depth-of-field) whereas the one on the right has a shallower depth-of-field. You’ll notice that the only change between the two pictures’ exposure settings was aperture. However, to achieve the same exposure, I had to make an offsetting change to the shutter speed. Notice that the shutter speed in both cases is faster than 1/115 (see rule of thumb!) which allows me to take a hand-held shot without the unwanted effect of camera shake.
While we’re on the subject, there are several different ways to achieve a shallow depth of field:
- aperture. A larger aperture (low number) like 2.8, 3.5, or 4.6.
- focal length. All else equal, a longer focal length (>50mm) will provide shallower depth-of-field than a wide-angle (24mm-50mm).
- distance between lens and subject. you can create a shallow depth-of-field by getting up close and personal to your subject. This can actually be done using a point+shoot camera. All lenses have a minimum focus distance, meaning you can’t get too close because the camera is unable to focus. This is where MACRO lenses come into play. These lenses have a much smaller minimum distance requirement.
The two main ways of balancing exposure are through shutter speed and aperture. A third, somewhat artificial tool is ISO and should be your last resort. On most cameras, the ISO ranges from 100 to 1600. A higher ISO will help increase your exposure (i.e. brighten your picture). However, this effect will come at the expense of a grainier picture which may result in a desirable texture. ISO is primarily used in scenarios where you have set your desired shutter speed and aperture combination but the exposure is still too dark. You cannot allow more light to hit the sensor for a variety of reasons: either you can’t slow down your shutter speed anymore (to avoid camera shake – see rule above) or you cannot increase your aperture anymore (because you have either already reached your lens’s physical limit OR you don’t want a blurry background). This scenario leaves you with three options: 1) add light from an external source (flash), 2) capture an underexposed picture or 3) increase ISO.
Shutter speed, aperture and ISO are only relevant if you plan on manually controlling your exposure (manual mode or “M” on the settings dial of a Canon). All other settings will automatically properly expose your frame. However, there are semi-automatic settings like Av and Tv; these settings stand for aperture priority and time priority, respectively. Av allows you manually set a desired aperture level (to achieve a specific depth-of-field, or background blurriness). When using Av, you only need to worry about is the aperture. The camera automatically figures out the shutter speed and ISO to create a proper exposure. Tv is similar in that your only concern is to set a desired shutter speed (to either freeze motion with a fast shutter speed or create a motion-blur effect with a slow shutter speed). The camera will automatically determine the appropriate aperture and ISO to balance your manually set shutter speed and achieve a proper exposure.
I’ve made references to the word blur a few times in this post but they are all different. I want to make that distinction:
- camera shake. this is when the entire frame looks blurry because you used a shutter speed that was too slow (and without a tripod). This is a blur effect that you want to avoid 99% of the time (unless you’re going for an abstract effect).
- motion blur. this is an effect that is made intentionally and also through the use of a slow/long shutter speed. However, you’ll have used a tripod (or other stabilizing object) and there will be a mix of mobile and immobile objects in your frame. The immobile objects (water, etc) will come out blurry while the mobile ones will be sharp.
- bokeh. This is the blur you achieve when creating a shallow depth-of-field. It’s technically not a blur, but many people will call it that. This is also an intentional effect that’s often used in shooting food.
How to Read for Exposure
SLR’s have what’s called a light meter. This is a visual guide that helps gauge exposure and is located in at least two different places on a camera: one inside the viewfinder and second on the LCD screen. The light meter is activated when you point your lens at something and press the shutter button down half-way.
A picture is properly exposed when the reading(i.e. hashmark) is at 0, or in the middle of a light meter. Anything to the left of the zero (a negative number) yields an underexposed photo while anything to the right of the zero (a positive number) yields an overexposed photo. The farther away from 0 the hashmark is, the more over/under exposed it is. You can even measure the actual amount of under/over exposure using a term called “stops”, which goes beyond the scope of this tutorial (if you’re at -1, your frame is 1 stop underexposed and at +1, you’re 1-stop overexposed).
The chart below shows three different screenshots (on the LCD screen). The left snapshot is that of an underexposed photo (-2), the middle is properly exposed (0) and the right most snapshot is overexposed (+2).
If you pay close attention to the snapshots above, you will notice that the only change between them is the shutter speed (1/100, 1/25 and 1/6). The aperture, at 3.5 and ISO at 3200 (my camera’s ISO goes higher than the standard 1600) were held constant. In this example, I used the shutter speed alone to alter the exposure.
If we were to look at the actual pictures of these light meter readings, they would look like this:
Why You Would Want to Manually Control Exposure
You’ve probably read this section and wondered why you need to learn the intricacies of exposure when you ultimately want to properly expose your picture anyway (in which case, why not just shoot on automatic??). The answer — you don’t always want to properly expose your picture! There are times when you want a dark scene and other times when you want to intentionally make a bright scene. This brings me to a very brief discussion on metering modes. Your camera has different ways of reading exposure. The default setting, which I believe is called evaluative metering, takes an average of the entire frame. Spot metering, which is what I use and prefer, only reads the middle point of your frame for exposure. Spot metering gives you a lot more precision in controlling exposure throughout your frame.
Having a working knowledge of exposure (i.e. shutter speed, aperture and ISO) will lead you to understand how to utilize features like depth-of-field and keep your pictures sharp (free of camera shake). Even if you ultimately decide to expose your pictures properly (not too light, not too dark), you should still get to know the features of your SLR. Control is, after all, one of biggest selling points of an SLR!
Food Photos Exposure Settings
Now that you’ve got the theory down, let’s figure out how you should set your camera settings when taking food shots. I always shoot on manual (that’s how I was taught), but a good second option is Av. Aperture, or depth of field, will probably be your most effective tool in creating a stunning food shot. Av will allow you to control that aperture while allowing the camera to automatically balancing for shutter speed and ISO. Just be cognizant of camera shake, which your camera will not warn you about!
Since I usually shoot using natural light and have a northern facing window (light not as bright), I often find myself using a higher ISO (around 800-1600). This provides me enough flexibility to change apertures (2.8 through 5.6) if I want while keeping a shutter speed that’s fast enough to avoid camera shake. I can always use a slower shutter speed, which would give me more options, but would come at the expense of having to use a tripod (something I’d rather avoid).
Some examples of food photos below with their exposure settings. Stay tuned for the next post in this tutorial series on LIGHT.