How many lens do you need for photography?

You are a student or lack of money

one lens only:  24-105 mm for every thing

You have some money:

1. 24-70 mm

2. 70-200 mm

3. 150-600 mm

You  are not short of money

1. 15-36 mm

2.  24-70 mm

3. 70-200 mm

4. 100-400 mm with canon or 200-500 mm with Nikon

5. 600 mm and 800 mm

6. 12 mm wide angle and 100 mm macro

If you are a professional:

fixed zoom