One of the lenses I purchased has this note in the instruction manual: "Do not place lens in direct sunlight or leave it in an extremely hot place such (sic) inside a car. Doing such could damage the internal parts of the lens or cause a fire".
Therefore, there are two parts to my question:
Can sunlight really damage a lens? I mean, aren't lenses made for using in various situations, such as in sunlight? If I can't shoot in sunlight (obviously not pointing the lens directly to the sun), it makes the lens much less of the good deal it appeared to be.
Can storing a lens inside a car in sunlight damage a lens? I don't necessarily want to carry all lenses I have in my car with me all the time, so forbidding storage of a lens inside a car for short periods (at most few hours) takes away some of the value the lens has to me.
If it matters, the lens barrel is plastic. And of course, if storing the lens in a car, I have caps on both ends so I won't start a fire!
I find it hard to believe that sunlight would be hot enough to permanently deform the plastic parts of the lens in few hours.
But then again, I do know in some parts of the world sunlight causes car plastic parts to deteriorate, albeit very slowly, so certainly the car shouldn't be where you keep your plastic-barreled lenses all the time completely exposed to the sun.