Tonight’s class was all about the differences between Aperture Priority and Shutter priority. I still have not received an answer on how to get auto-focus to work with live view. Anyone that knows how to do this on a Canon Xsi, please let me know.
The other stuff we talked about was how to eliminate blur. Blur can happen for two main reasons. The first is camera shake. This is caused by the photographer not being able to hold the camera still during the shot. The best way to eliminate camera shake is to make sure your shutter speed is fast enough. Using the formula
shutter speed = 1/(focal_length * crop factor)
Each camera has it’s own crop factor. Some common crop factors are:
Canon = 1.6
Nikon/Pentax/Sony = 1.5
Olympus = 2.0
So if you were shooting with a focal length of 100mm on a Canon your shutter speed would need to be at least 1/160 so you would have to use 1/250. As you change the focal lengths you run into a problem with not having all of the aperture openings available (Unless you have a fixed aperture lens, which are pricey). So it may not be possible to get the shot with the shutter speed. You may have to increase ISO, which we learned is bad, or put the camera body on a tripod of fixed surface. (remember to turn off image stabilization when you do this).
The other cause of blur is due to motion of the subjects. There are three factors that you have to take into account for this:
1) Speed of the motion of the subject. A slow moving subject will produce less blur than a fast moving subject.
2) The direction of movement of the subject. A subject moving away or towards you will have little blur while a subject moving across your field of vision will have the most blur.
3) The distance from the subject. A subject very close will produce more blur while a subject in the distance will have little or no blur.
One other subject we discussed was Depth of Field. Aperture settings can significantly effect DoF and focus of your subjects are impacted based on focal length and aperture settings. There are a ton of free and for-fee programs that will help you figure out DoF. There are three free ones available on the iTunes store.