Why Are Parts of My Image Out of Focus?
Have you ever seen those amazing looking portraits where only the main subject of the frame is in crisp focus and everything else in the background is completely out of focus? Have you been fascinated by such an effect? Most of the point and shoot photographers actually move to DSLR or mirrorless photography for this effect only. But the truth is that it is not about the camera only. It actually depends more on camera settings and specifically, it depends more on aperture settings. You will struggle to achieve this effect if you have to rely on your camera’s Auto mode.
In the photos above the first two images were taken with a wide open aperture (f/2.8). The last image was taken with a small aperture (f/22). Notice how everything is in focus on the rightmost image. You can recreate the same effect if you are a nearsighted person. Make a small hole in a piece of paper about 2 millimeter in diameter and look through it without glasses. Everything you look at is suddenly in focus. This is exactly the same principle as the image above on the right where the camera was set to a small aperture.
Deep or Shallow Depth of Field
This is the trick (depth of field) that portrait photographers use to blur out the background. But as with all things, too much of a good thing is not always good. Open up the aperture too wide and you might have a problem where a certain distance from the camera is in focus and none of the rest is. For example, if the bride in your shot is in focus, but the bridegroom standing a couple of inches back is not, the photo will probably not be a good one. On special lenses the aperture can open extremely wide – so much so that if a model poses for a close-up face shot, some images will have the eye ball in sharp focus while the eyelashes mere millimeters away are out of focus. This is typically the case on apertures of f/1.4 and wider.
The Meaning of F-Stop
Aperture is indicated by your camera with an f-stop, and is a measurement of how wide the hole (aperture) is that funnels in light into the camera. The number you see, for example f/2.8 or f/22 seems a bit counter-intuitive, as an f-stop of f/2.8 indicates a bigger aperture opening than f/22. F/4 would for example be a setting favored by portrait photographers who want an out-of-focus background, while f/22 would be preferred by landscape photographers who want everything in focus – from the foreground to the background. Watch out for settings smaller than f/18 as the extremely small aperture can lead to an amount of distortion on your image.
How Does Aperture size Tie Into Depth of Field?
If we go back to the third image above where everything is in focus on the chess board, we can see that a small aperture size was used (an f-stop of f/22). The depth of field is deeper, that is, more of the picture is sharp and in focus. Conversely, a wide aperture will lead to a shallower depth of field. In a future post we will cover how to focus on a specific point/distance to ensure that only that area is in focus.
How Good is Your Camera’s Auto Mode At Controlling Depth Of Field?
So far we have seen that the auto mode can, in its attempt to expose properly:
- expose its sensor to light for a longer span of time
- or open the aperture wide for a flood of light.
We do not know what option Auto mode will choose to help you take a photo. In the case where you take a landscape photo for example, you would not want Auto mode to open the aperture up wide as you might end up with the mountains in the distance out of focus and only a shrub 15 feet away in focus. The problem is you do not know what option Auto mode will choose, and that is why you need more control.
Finally what do we do at a wedding reception if the lights are dim and we cannot open the aperture any wider and every shot still exposes too long (soft and blurry)? There is one last weapon in a camera’s arsenal and that is ISO, or sensitivity.
We will cover that in the next article.