One of the DSLR‘s key strengths is the capability of using a massive range of lenses. Anyone you talk to about camera’s whether it be photography or video they will say to pay for good lenses. You can always buy a new camera and the lenses will work on all cameras.
Canon has 3 tiers of lenses. They have the “kit lenses” which are what come with a camera kit. These lenses are the cheapest in price and typically start at an aperture of 3.5 and go to 5.6. The next level up will have a gold ring around the lens. These lenses are a little faster to focus bust are still reasonably cheap and the aperture settings are the same. The best lenses are the L series lenses which have a red ring around them. Some of these lenses are white. These you will pay top dollar for because of the glass and most of these lenses are fixed aperture.
What does that mean? As I mentioned earlier, the cheaper lenses have an aperture reading of 3.5-5.6. This means that the lowest aperture you can get zoomed all the way out is 3.5 and the lowest aperture you can get zoomed all the way in is a 5.6. Basically the lens can’t maintain the aperture as it zooms. In photography this isn’t the end of the world because you can then adjust your iso or your frame rate to compensate for then exposure. Now you will lose your shallow depth of field.
With video this is a disaster because video is continuous. If you’re shooting with a kit lens and you are zoomed out at 18mm at 3.5 and then you want to zoom in at 55mm at 5.6 you will see the image get darker right in front of your eyes. Again, this is because the lens can’t maintain the aperture and it has to adjust accordingly.
If you are using an EF 16-35mm f/2.8L lens you could be shooting at 16mm and then zoom to 35mm and your exposure would not change because the aperture would stay at 2.8 also keeping your shallow depth of field.
There are also prime lenses which are more expensive because they have no moving components. They a fixed mm and the image quality will be a little better with these lenses.