I keep meaning to do a long post on food photography, but never seem to get around to it. I started one here, but never really finished it. Posts on food photography is one of New Years resolutions, so now I have no choice but to do it! I am going to change my plan of attack though and start with a bunch of shorter posts. I am going start with illustrating the basics and then focus on using flashes to do food photography. A lot of these topics are covered in general photography books, but things are a little different when you are focusing a plate of food two feet away verses than a mountain range.
The first topic I am going to cover is depth of field, which is the amount of stuff your camera can have in focus at once. A large depth of field means that objects at a wide range of distances are all in focus at the same time. A shallow depth of field means that the focus will be very selective. You maybe able to keep one thing in focus and everything in front or behind it will be blurry. I am not a photographer, so I am going to keep it simple and explain it the way I understand it.
The depth of field is controlled by the aperture of your lens. The lens has metal blades which snap together right before each photo is taken. The size of the opening these blades make is the aperture, which is measured in f-stops.
Here is where it gets tricky. A smaller opening corresponds to a larger depth of field and a larger the f-stop number. Most lens’ highest f-stop is 16 or 22, which is a really small opening. Lens will have a lower f-stop of anywhere between 2 and 4. When the aperture is set to these lower f-stops, the metal blades do not close at all, letting as much light through as possible. With the lens blades wide open, the area in focus is very small.
There is one more fun relationship that you might have guessed. As you make the size of your aperture smaller, you need more light to get the correct exposure. In order to increase the depth of field and get more of the picture in focus, you need to get more light. The are a couple of different ways to get more light:
- if you are using flashes, you can increase the power of the flash
- if you are using light from a window or lamp, you can keep the shutter open longer
- make your camera more light-sensitive by increasing the ISO speed
There is one last thing to remember when thinking about depth of field–the camera’s distance from the object you are trying to photograph also effects the depth of field. The closer you get to an object, the smaller the depth of field. When you get really close to a plate of food to capture some detail, it becomes harder to have the whole plate in focus. As you move closer to an object, you have to increase the f-stop to keep the same depth of field.
Here is a chart to help illustrate how depth of field is affected by all of these different aspects, with the arrows showing the direction of the relationship.
Right about now you are probably pretty confused. The thing to focus on (pun intended) is that you control how much of your photo is in focus by change the depth of field by changing the aperture or f-stop. There is a lot of math going into all of this, but luckily there is an online calculator which lets you see how all of these aspects are related.
Additionally, cameras have gotten very smart. Simply set your camera to Aperture Priority mode and it will do the rest. You can choose an f-stop and the camera will do the rest to ensure that you get the correct exposure. The f-stop depends on what look you are going for. If you are using an SLR camera the view finder will look the same no matter what you set the aperture to. This is because the camera opens the aperture up all the way for focusing and only shuts it down when a photo is taken. Most SLR’s have a depth of field preview button which stops down the lens to the aperture you are using and gives you a preview of what your depth of field will be.
The real question is why would you want to do this? Well, being selective in focusing can direct the viewer towards the important parts of the photo and blur away clutter. At the same time you want to have enough of the photo in focus so the viewer can figure out what is going on. This is where composition and artistry comes into play.
Below is the same photo taken with different f-stops. This should help you better visualize the effects you can create. If you want to include everything that is on a plate, use a higher f-stop. If you want to focus on a detail, go with a lower f-stop. In order to keep the exposure the same for each photo, I turned down the flash each time I stepped the f-stop down. I started at f 8.0 because that was the highest f-stop I could get with my flash turned up all the way. If I wasn’t so lazy I could have increase the ISO sensitivity of the camera. Photography is full of trade-offs!
The lighting setup I used is below. It is a single flash, shot through a soft box. There is a small piece of foam core opposite the flash to help fill in shadows.