Originally Posted by
Tiki
I am a total beginner in DSLRs, I don't understand what "stops" are. Which of the lenses packaged with the Canon 450D would be better?
For the purposes of the Africa trip, the most likely scenario will be shooting birds out a car window, at picnic spots where you are allowed out of the car and in the rest camps. This will be northern Kruger-Punda Maria and Pafuri picnic spot.
A "stop" refers to doubling or halving the amount of light for the exposure. When everything else stays the same, a 1/30sec is "one more stop" than a 1/60sec one, as you get double the light getting to the sensor/film. Similarly a f/8 aperture is "one stop lower/less" than a f/5.6 if everything else stays the same. It can also be used for ISO. Switching from ISO100 to 200 will "gain you one stop" if everything else stay the same.
The 18-55IS and 55-250IS package is a very good value. Both lens have good IS and great optics, though construction and the focusing speed are not the best, as they use Canon's micro motor (MM) and not the ultrasonic motor (USM).
For birding trips, you may find these lenses inadequate with focusing speed as well as reach. And there are some alternatives that can still be "fairly affordable". One very popular lens that's been around for a long time is Canon's 100-400/4-5.6L IS. It has very good reach at 400mm, but is still handheldable. It's about US$1,400 here. Or the "Bigma" - Sigma 50-500, which is about US$1,000. Both of these lens are quite popular with people shooting wild lives.