I know about 17-55 f2.8 and the likes of it, but I am talking about something say 18-135 f2.8. There exists 70-200mm f2.8 and the range (200-70 = 130mm) is much bigger than in 18-135.
I am aware of the meaning of f numbers being a ratio between focal length and the effective size of the aperture. The key point being "effective size of aperture". E.g. 600mm f4 does not mean that the blades open up to 600/4 = 150mm.
- Are they impossible to make due to laws of physics?
- Would they be too heavy/long making them unusable?
- The range is not the only factor. I am hoping that this is correct, but why?
P.S. I use a Canon 60D and my questions are for the 1.6 crop factor sensors.