Replying to
>>3724827 from the other threadTake some pictures and find out. You don't want dust in the lens but honestly most of the time it's outside of the focal plane so you can't really see it. Though, significant enough contamination could be visible, and depending on the element that is contaminated (element being a single piece of glass inside of a lens, of which most lenses have several), it could become visible on the end photo.
It is best to keep caps on both ends of a lens when not in use, and clean them if you notice contamination at all.
On a "professional" lens as you say, these are usually sealed from the elements and constructed in a clean room, if you are seeing dust inside of a weather sealed lens you may have bigger problems at hand. Obviously they are still subject to the same contamination on the outside glass and the backmost glass that is closest to the mirror/sensor.
A lot of guys will run a cheap polarizing filter or just a blank glass filter on the front to protect their lenses from scratches, dust ingress, etc. The filter itself may not do anything at all to the optical output, but would be used to be a disposable/expendable sacrificial piece of glass if something were to happen, so the much more expensive lens' integrated glass is still protected.
For that lens, it is one of the cheapest lenses you can get from Canon, it's very cheaply made, and it's no surprise there's dust inside it. That said, it can still be usable and take surprisingly good pictures if you know what you are doing.
My advice to you is to take a bunch of pics, some of neutral backgrounds/colors and see if you can detect any dust on your final picture, if not, shoot away. Use that kit lens to its fullest potential, don't gearfag. Get absolutely familiar with how the lens performs, perfect your methods, and only then move on to more advanced gear.
