system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a microscope not show the microbes on its own lens?

I hope I worded that correctly so you can understand my question.

So I'm pretty much thinking "Ok, so a microscope is essentially a big 'zoomer' - it'll show everything in front of it magnified by... a bunch. So, there are germs on everything, right? So there's got to be germs on the lens of this thing. But I never see them? Or, for that matter, the germs ON TOP of my glass slide??"

Apologies if I'm using incorrect terminology here. Obviously this isn't my area of expertise. Hopefully this makes sense.

Also I did do a search and couldn't find any similar questions.
gpt
A microscope is essentially a series of lenses.

You know all those knobs on the side of one? They adjust the distance between the lenses and/or the distance between the slide and the lens apparatus.

The reason they do that is because lenses have *focal points,* which are points outside the lens at which light projected through the lens will converge--or, in more familiar terms, a point that the image is the most crisp and clear. 

When an object is moved into the focal point of the lens apparatus, it becomes magnified. Outside of this point, it's blurred. If it's too far outside, it's blurred so badly that you can't even see it. 

Microbes on the lens are too close to the lens to be anything but horribly blurred, to the point where you can't see them except maybe as a slight tint to the light. Microbes on the slide, you could probably see if you focus on them.