Friday, January 1, 2010

All about the focus...

It happens to everyone. You take a great photo of an event. You preview the image on your computer and disappointment sets in. The entire photo looks blurry. What went wrong?
What is causing these blurry digital photographs? 

There are a few reasons, and it's not related to how the camera is working, but unfortunately the photographer behind the camera and the set up chosen on the camera.

When you use a lens with a long focal length, camera shake becomes more pronounced. 

When you have your lens set to wide angle (20mm) the lens is stable. When you look through the camera viewfinder, you should not see a lot of shake or movement.
When you zoom in on a subject and extend the lens. At a long focal length (200 to 300mm) you should see a slight jiggling when you look through the camera viewfinder. Currently there are lenses that help stabilize this, VR or IS depending on the system you own.
You can use a long focal length, so long as you set your shutter speed fast enough so that the camera shake is canceled out. The general rule of thumb is that you should not use a shutter speed slower than 1 over the focal length of the lens when you are holding the camera in your hands.
At 20mm, you should be able to get a clear photo with a shutter speed of 1/25th of a second. At 200mm, you have to increase the shutter speed to 1/250 of a second to get a clear photo. At 600mm, you had better be using a shutter speed of 1/700 of a second.
If there is not enough light to support these shutter speeds, then you have a few options.
1: purchase a camera that has vibration reduction (VR). VR is a mechanism within the lens that helps minimize shake even at long focal lengths so you can hand hold a slower shutter speeds.
2: place the camera on a tripod, which also helps eliminates camera shake.

3: Increase the ISO the camera to increase the sensitivity of the sensor

4: Open the aperture to allow in more light (if possible)

Slow Shutter Speeds
Slow shutter speeds will cause blurry photos every time. You might wind up with a slow shutter speed and be unaware of it if you have your camera set to aperture priority mode. In the "A" (aperture priority mode), you select the aperture and the camera determines the appropriate shutter speed to get a good exposure.
Say you have your camera set with a focal length of 100mm, an aperture of f8.0 and a shutter speed of 1/125. You are taking photos in bright daylight, and with these settings the photos should appear clear.
Now the sun dips behind a cloud. Your focal length is still 100mm, your aperture is f8.0, but the camera has adjusted the shutter speed to 1/60 for the correct exposure. Now your photo might appear blurry.
If all of these numbers seem overly complicated, here's the general rule to use: try to avoid shutter speeds slower than 1/125 of a second when holding the camera by hand. This covers all the focal lengths from 20 to 125, which is a pretty good range (a 3x zoom typically goes from 35 to 105mm).
Wide Apertures
When you use a wide aperture setting on your camera (f2.8 for example), you significantly reduce your depth of field. Sometimes, you can reduce the depth of field so much that the object you focus on appears clear, but another object less than an inch behind it is fuzzy.
Think of it this way: you take a photo of a flower with an aperture of f2.8. You have the focal point selected for the bottom of the flower. Due to the shallow depth of field, the center of the flower will be out of focus.
This problem is especially significant when you use a long focal length lens. As you increase your focal length, you further reduce the depth of field. So a long focal length and wide aperture will give you a shallow depth of field and compress you image more. The closer the subject the shallower the depth of field will be.

Think of it this way. 

You are photographing a statue 50 feet away, the focal length is at 70mm, your aperture is set to f2.8 and you shutter speed is 1/250th of a second. More of the image will be in focus, due to the distance you are from the subject. 

You then zoom in to 200mm, at f2.8, the shutter is reduced to 1/125th, VR is on, but you have compressed the overall image and have a much tighter shot of the statue, the background behind the statue is now out of focus.

Below are two images that show what changing your perspective, depth of field can do.

Top Image:
16mm, f9, ISO 200, 1/800th of a second


Bottom Image: Same settings
16mm, f9, ISO 200, 1/800th of a second


Here is a quick summary of the issues and solutions for getting sharper photographs.

Blurry Photos
Increase your shutter speed so that it is greater than or equal to 1 over the focal length
or Increase your shutter speed to a minimum of 1/60 to 1/125 when holding the camera in your hands
Get a lens with vibration reduction (VR) technology 

Increase the ISO
Turn on the flash (if needed) 
Use a tripod

If shooting with a simple point an shoot camera, keep in mind you are limited. The point and shoot cameras can only do so much and are limited in their adjustments

Settings I recommend:
ISO 200-400
Flash "On"
AF-S mode
Leave the camera in "Auto"

Most of the time the P&S type cameras are used for snap shots of friends and family. So the settings above will help ensure sharper and clearer images.