For your Cannon 550, the ‘normal’ lens would be a 35 mm.so the 28-80 would cover a good range from (slightly) wide to a good portrait lens (a short telephoto.) i use a 35mm on my Nikon ‘crop sensor’ camera. It turns out that the sensor on most dslr cameras has better resolution and dynamic range than all but the most expensive astronomical ccd cameras. The sensor on your camera is a cmos sensor, similar to a ccd, but less expensive to produce.