Lenses

[adrian078]

In theory if the lenses were perfectly manufactured with no optical faults and were exactly the same and you had the same aperature, the image would look the same.

However, in practice quality and lens construction varies, even 2 lenses exactly the same model would vary(although this would be minimal).

The other thing to keep in mind is that lenses don't perform their best at extremes e.g. for the 18-55mm lens, it might suffer from more barrel distorition or have more chromatic aberrations at 18mm. Generally you will lose some sharpness at the extremes.