Small Focal Length Question on Lenses

[Bryan]

All,

This seems like such a dumb question, but I was looking through lenses and it occurred to me: why are lenses sold with relatively small focal length ranges? For example, in the 18-55mm range provided by my D3100's kit lens, I could buy the following from Nikon:



17-35 f/2.8
16-35 f/4
18-35 f/3.5-4.5
16-85 f/3.5-4.5


I'm certainly not asking for the pluses and minuses of each lens, but I don't understand why there are so many focal length choices in the same range. Yes, I realize that the apertures are different, but why would I want an 18-35 f/3.5-4.5 to supplement my 18-55 f/3.5-5.6, or why would I want two lenses when I could just use one?

[smaeda]

Unlike prime lenses, where all lens elements can be utilized to maximize the image quality at a single focal length, zoom lenses have to make trade-offs between image quality, focus, and various optical aberrations. Smaller zoom ranges usually tend to have better IQ throughout the focal range, while lenses with larger zoom ranges often have a sweet spot where IQ is at its best, which falls off as you move towards the extremes.

[Bryan]

That answer makes a lot of sense. I guess I just have a feeling most "people who like taking pictures" like me (I would not currently call myself a photographer :oops:) probably couldn't tell the difference.

[smaeda]

You would be surprised. Once you start shooting with a decent lens, the IQ difference becomes extremely noticeable. I copied and pasted the above reply by the way. lol.

[Bryan]

I copied and pasted the above reply by the way. lol.I thought it seemed a little too "by the book" :lol:

So basically it's a matter of IQ going up as the focal range goes down (in general), right? That said, lenses like the 24-70 exist because sometimes you just can't have 5 lenses in your bag at once and expect to catch the moment?

[roy obanion]

Also different ones are released at different times. Some of those are older lenses and some are newer..and some are DX only (crop sensor), others are FX (full frame compatible)

[Bryan]

Good point. I didn't think about that.

Still, I was wondering why you'd have, say, an 11-16 for wide shots. Why do you need such a narrow focal length? It's not like 18-55, 55-200, 24-70, etc. where you're covering from wide to narrow-angle...wouldn't you be better served to just have a prime?