If you are using a prepared slide, they can easily collect dust on top and on bottom of the slide. Then may see these dots or defocused circles from the dust on the slide. Use a microfiber cloth and gently clean off both side of a prepared slide. This is the easiest and safest area to clean, so always start with this step.

Also dust here is closest to your focal plane, so it will be the most distracting. You can also tell if its dust on the slide, if you move the slide position and the dots move with the slide. If the dots stay in the same place in the field of view, they are in the optical system so proceed to the next areas to clean.

The best way to avoid dust on the eyepiece is to keep them in their original container when the microscope is not in use. Also, you NEVER want to leave the drawtube open and exposed to dust – the drawtube should ALWAYS have the dust caps or the eyepieces installed at all times. If dust gets down into the drawtube area near the other optics and prisms, it can be very difficult to clean and may damage the optics.

If your eyepiece has gotten dirty, most likely its the outside surface near where you place your eye, use a slightly moist microfiber cloth and gently wipe off the outer surface. If you left the eyepiece out unsealed at any time, you can also wipe off the inner surface as well.

If you are using a prepared slide, they can easily collect dust on top and on bottom of the slide. Then may see these dots or defocused circles from the dust on the slide. Use a microfiber cloth and gently clean off both side of a prepared slide. This is the easiest and safest area to clean, so always start with this step.