Lenses come in all shapes and sizes - listed below are some types of lenses and what they do, I will talk as if you have a cropped sensor as most people who need advice on lenses and focal lengths will probably be using a cropped sensor body:
Wide angle lenses - from 10mm - 50mm. those at 10mm-15mm are usually 'fish-eye' lenses where they are so wide, you'll struggle to keep your feet out of the frame. have a very wide angle of view - sometimes up to 180 degrees and beyond
'Normal' lenses - around the 35mm mark (50mm on a Full Frame) - see roughly what the human eye sees, hence photos have a very natural feel about them
Portrait/Short telephoto Lenses - The photography gods say that a good portrait length is roughly between 50mm and 105mm on a full frame camera, so roughly 75mm to 113mm on a cropped sensor. This sort of focal range is good for portraits, weddings and as a general walkabout lens. usually 18-55mm would be a short telephoto, alternatively 24-70mm etc etc
medium/long telephoto lenses - These are generally for wildlife and sports photography, although 200-300mm top end can also be used as a wedding/portrait lens. They tend to be very heavy, and the better/faster lenses (constant F/2.8 aperture) are very very heavy and very very expensive. Someone aptly described them somewhere as a 'paedo lens', cos they look quite noncey.
Prime / fixed focal length lenses - do not zoom at all, hence you have to 'zoom with your feet', but they generally offer excellent picture quality (even the cheaper primes), and they are generally extermely fast (opening up to 1.8/1.4/1.2 in expensive lenses). You can get primes lenses at all types of focal lengths, and photogrpahy 'purists' often only use these and not zooms, although the quality of zooms now is such that you don't need to have lots of primes, unless you are a poncy geek.
MAKE SURE YOUR LENSES ARE COMPATIBLE WITH THE MAKE/SENSOR ON YOUR CAMERA!
Compatability with cannon 5D lenses:
Thanks to Rodney once again!
Trust me, I did so much research on what lenses were Full Frame compatible when I made the switch! Avoid Sigma DC and Tamron Di II!
Right. Firstly sell the 10-20 unless you want extreme vignetting!
For wide angle, look at the Canon 17-40 f4L. That will almost be as wide as your Sigma. Try for 2nd hand as they are costly.The 24-105 covers your walkabout range The macro is a good macro A 70-200 f4 (is) would be good - they're fairly cheap (explore the sigma option if you want it cheaper) And you can't go wrong with a 50mm f1.8 on Full Frame.
Cannon 50mm 1.8 'nifty fifty' - An absolute no brainer if you have a cannon DSLR - £75 quid new, just buy one already
Cannon 'L' Glass - Top of the range lenses from Cannon - built like brick shithouses, fast as you like (constant f/2.8 throught the focal range) and crisp across the focal range and wide open. Will potentially get you divorced due to the massive cost, but you get what you pay for - i.e. great photos and envious looks from the proles.
I have attached a link here for ALL Nikon lenses in existence - if you can't find it here, it doesn't exist:
http://www.photosynthesis.co.nz/nikon/lenses.html if you visit this website and it's helpful please thank the guy or click on his ad links please
Here is a similar list for Canon Lenses before i get shouted at:
http://www.bobatkins.com/photography/reviews/best_canon_eos_lenses.html
again, if this is helpful to you please click on the guys ad links or say ta if you can
