as far as I know yia, the human eye sees around what a 50mm lens sees. So 35mm and below are considered wide angle lenses. and 85mm and up are considered telephoto.
anything below 18mm I think they call fisheye.
what you are experiencing is probably someone calling the lens a 24mm lens, and someone else calling it a 24mm wide angle lens. but its probably the exact same lens. (the first person is just assuming that you know its a wide angle)
youre exactly right ...24mm is one and the same...It is just some marketing ploy to get the sale. PS if you are to use 24 mm with a slower lense.. you better light up your scene with a lot of light. I tried it with the letus..no go..grainy..at best. I now have a better adapter but still you have to light it hard to get your lens turned down for focusing.
Is there all that big a difference between 24mm and 28mm? I have a 28mm with an f stop of 2.8 + and I get a little bright spot in the middle with it open all the way. Is that typical with wide angle lenses? http://i97.photobucket.com/albums/l233/poddusoleil/56007955.jpg
the difference between 24 and 28 should be pretty noticeable. the lower the numbers the more the difference between them. On the other hand the difference between a 180 and 200 is very minimal.
But I'm not aware of anything that would say a wide angle lens should have a bright spot when fully open in the center. (it might be your lens.)
Also make sure you get a good piece of glass when you're going that wide. I've got a 28 and a 24 that I don't use anymore because they simply blow. I spent a decent chunk on a 20mm (about $400 used at KEH) and it's awesome. Super minimal field curvature and a nice f2.8 speed.
There many places to look..I found my 24mm from an ad in craigslist..paid $60USD hard cash. because the lady was just getting rid of it ASAP and didn't care to go thru auctions.