Many combinations of aperture, shutter speed and ISO will give us correct exposure. For example, ISO 100, F4, 1/250, F5.6, 1/125, F8, 1/60 and ISO 200, F8, 1/125 will give us same correct exposure in terms of brightness of the photo.
Which correct exposure setting to use?
Well, choose the combination that gives us the desired effect. In order to know what the desired effect is, we need to know the effect of aperture and shutter speed setting. For ISO, use the lowest possible as lower ISO gives us better quality with less noise. However, as mentioned before, crank up the ISO when necessary to avoid blur image. Image with noise is still better than unintentional blur image. Image with noise can be improved significantly in the retouching software nowadays.
Aperture and depth of field
Depth of field is the distance that appears to be in focus in front of and behind the focus point. It is affected by aperture, lens focal length, and the distance to the subject. The table below summarizes the effect of aperture, focal length and distance to subject on the depth of field. To achieve the shallowest DOF, use the largest possible aperture, long focal length and move in closer to your subject.
|Shadow Depth of field||Deep depth of field|
|Aperture||Wide (low f-number)||Small (high f-number)|
|Focal length||Long (telephoto lens)||Short (wide angle lens)|
|Distance to subject||Short||Long|
Here is the illustration of the effect of different apertures:
Shutter speed and motion
Fast shutter speed has the ability to freeze the motion and action to capture moment that our human eyes can’t see.
Slow shutter speed will introduce blur to the image and when use correctly can emphasize the motion and direction. However, bear in mind that you may need to mount your camera on tripod if shutter speed is too slow.
Below are example of images captured with slow shutter speed. Instead of getting a perfectly still image, now we can some some movement from the otherwise still image.
How to avoid blur image for static subjects?
- Pay attention to shutter speed
- Rule of thumb (without tripod)
- Minimum shutter speed = 1/(focal length)
- 200mm lens à min shutter speed is 1/200 s
- 50mm lens à min shutter speed is 1/50 s
- With VR/IS
- Vibration reduction / image stabilization
- Min shutter speed could be 3-4 stops slower
- 1/200 s becomes 1/15 s
How to avoid blur image for moving subjects?
Again, pay attention to shutter speed.
For slow movement, 1/100s or 1/125s is probably sufficient
For fast movement, you need faster shutter speed of 1/250s or 1/500s
For extremely fast movement, increase the shutter speed to over 1/1000s
Panning is an interesting technique that you pan your camera along with the moving subject to get a image with relatively sharp subject with blur background
This technique takes some practice to master it. The speed you pan is especially important as you need to anticipate the speed of your moving subject.
Below are some examples of panning effect: