Nothing is visible
Check that the light is on and the brightness is turned up. Make sure the lens above the slide has clicked into place and the sample is over the light opening. Start with the lowest magnification and move the slide slowly while adjusting the large focus knob.
If your microscope has a separate camera port, check whether a switch is sending the light to the camera instead of the viewing lenses.
The view is blurry
Try a prepared slide that you know is clear. If it looks sharp, your water sample may be too thick. If so try using a smaller drop with less debris. You can also remove excess water with cotton swabs for a slide already prepared.
At higher magnification, use the small fine-focus knob for tiny adjustments. If every slide looks blurry, look for fingerprints or dust on the viewing lenses and gently clean them with lens tissue.
P05 · Photo needed: the same sample blurry and sharp, at the same magnification.
Dark spots appear in every sample
Move the slide. If a spot moves too, it is on the slide or in the sample. If it stays still, gently turn the viewing lens if it rotates freely. A spot that turns with it is probably dirt on that lens. Clean the affected glass rather than adjusting the focus again.
The image looks washed out
Turn down the lamp brightness or if there is an iris lever beneath the slide, it adjusts an opening in the light path; close it a little to make faint edges stand out. If fine details become blurry, open it slightly again.
A clean slide and a thinner sample can also help. Some transparent organisms are naturally faint in brightfield, the usual bright-background view.