Dear, It is already the second time in a few weeks that I find the 20x objective dirty when I am to use it. Two things: 1> It is a dry objective. So no water immersion. And if you come back from the 25x, 40x, 63x objectives (water immersion) you should dry first your slide. 2> If you dirty it, you clean it. BTW: any good suggestion for cleaning? As I have been told ethanol is not the best. Unless, I noticed that the 405nm channel is not overlapping with the 488nm or the 514 nm channels anymore. It looks like a x or a z-shift. Anyone observed misaligned channels also? It is bit annoying for co-staining, co-localization experiments. Best Helene