Camera Labs

I am a newbie to DSLRs and have a Canon EOS 400D with the standard lens 18-55. I have two reasons for wanting to get a new lens. The first is that I take distance shots of dogs dashing across fields and can never zoom in close enough. I need to take photos without a tripod as we are on the move! The second is that I am going to Australia and don't want to take more than one lens. I have therefore been considering the Canon EF-S 18-200mm f/3.5-5.6 IS. Can anyone advise if this would be the best lens for me? If not, what would you recommend?
I hope I haven't made myself sound too dim, but the more I read and the more videos I watch the more confused I become!
Thanks

Gordon did a wonderful review of the EF-S 18-200mm.
I would recommend watching the video review of that lens at the very least.

Another option would be a Tamron 18-270mm as it has a longer range.

If you only want a single lens solution, that is what these lenses are designed for.
The trade off for the versatility/compactness/price is image quality, but that would occur for any super zoom you buy.
These are not bad lenses. They are absolutely fantastic for what they are intended for; which is a muti-purpose single-lens solution.

One thing you could do is rent a copy of the lens for a bit to see if that would work for you.

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Canon Rebel XTi, BG-E3 Grip
Canon EF 16-35mm f/2.8L II, 24-105mm f/4L, 50mm f/1.4, 70-300mm f/4-5.6 DO, 85mm f/1.8
Sigma 150mm F2.8 EX Macro
Sigma 10-20mm f/4-5.6 EX, Canon EF-S 18-55mm f/3.5-5.6 II
Canon 430EX II
Opteka 13mm, 21mm, and 31mm extension tubes

That's really helpful - thanks. I had considered the Tamron but read reviews that said the quality isn't very good. I tend to not shop often, so like to get the best quality I can.
Having spent the evening reading-up, I am now thinking about the Canon EF-S 17-85mm. Just don't really know...... I suppose if I go into somewhere like Jessops I can try them out?

I think I have decided on the Canon EF-S 18-135mm, which seems like a popular upgrade to the kit lens. All comments/thoughts very much welcomed!