Usually if you want the range like . . .
- 18-200
-18-270 by Tamron
- 18-250 by Sigma
- - - You won;t be able to enjoy better quality pictures in terms of Image Quality (IQ).
That's why I recommend a short focal Mid -> Zoom lenses.
Why? . . .Cos
- Short Mid -> Zoom lenses (ie, 17-50) have constant f2.8
- Better handling under low light
Canon EF85mm f/1.8 USM
Why I suggest this ? . . . Cos
- You already have a 17-50 range, no point buying 35mm, 50mm primes to overlap.
- Trust me, if you are shooting at outdoors, this lens is just nice ! I've borrowed this and shoot a couple of times.
- This is also a good street lenses for taking street pictures.
- Gives acceptable bokeh
- Very good handling under low light.
Canon EF-S15-85 f3.5-5.6 IS USM
Range is good, cos at 15mm you can capture beautiful landscape, and all the way till 85mm, you are able to capture streets, portraits blah blah, so on and so forth.
However, do take note that this lens might lose out compared to T 17-50 2.8 under low light.
Why I say this ?
- The meaning of low light,
Usually it depends on how fast the lens is. How much light can enter the lens. So the smaller the number of aperture, ie, f1.2, f1.4, f1.8, f,2.8
Bottom line;
In my humble opinion,
I feel that having just 2 lenses will do,
Tamron 17-50 f2.8
Sigma 17-50 f2.8
Tokina 16-50 f2.8
Chose either one.
Canon 85mm f1.8
Canon 50mm f1.8 - - - Okay, if you are "scared" about focal length, try this first. Cheap -- $110 off from the Buy Sell section easily can get one.