70 -300 g lens internal dust
Dust will happen. It is REALLY not a problem unless you live in a tropical / humid climate year round which could allow fungus to grow on a lens. In that case spend some bucks on a drier cabinet.
You risk doing a lot of damage to the lens in trying to get rid of internal dust in breaking the ring motor or decentering lens elements, which will massively degrade performance.
Overcleaning can do much more damage than dust as well in creating rub marks which are numerous fine scratches that hurt image contrast.
Read this article: http://www.kurtmunger.com/dirty_lens_articleid35.html
Even with the front element of that lens cracked in half the image is salvageable!
I've taken numerous pictures with a dusty lens that I later cleaned and then took pics of the same scene, can't tell the difference... ever!
The only particles/stuff that will degrade or change image performance is grease/oil/water type stuff. A smudged lens will produce softer images, which is why fashion photogs often put Vaseline on a filter. Water droplets act as a lens in themselves and will show up in an image even if they are small, since they change the direction of the light. So those two things might/are worth cleaning.
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