A roundness of water drops
Raindrops on salix chaenomeloides (Japanese pussy willow) imaged in Belgium by Fabien Buisseret.
Image ©Fabien Buisseret, shown with permission
The surfaces are hydrophobic and so the drops rest on hairs rather than spread to wet the tissues.
Tiny drops, large drops. Large ones are likely from several raindrops run together. Look carefully, the larger the drops the more they distort from spherical. Water molecules attract each other and these attractions unbalance near the liquid surface. The surface tries to shrink as small as possible - surface tension. A sphere has the smallest area. In large drops, surface tension is less important than gravity and other disturbances. Large drops distort the most.
Rainbows rely on almost perfectly spherical raindrops. deviations from spherical of only 1-2% blurs a bow. That is one reason they are so rare and why more poorly wrought ice balls or hail do not make bows.
Raindrops act as lenses. At top right they make small inverted views of the garden.
Raindrop lenses are poor affairs afflicted with a defect appropriately called spherical aberration. They cannot focus rays to a single point. Their poor focus helps form the heiligenschein glow on dew or rain wetted grass as does their predilection to sitting on hairs.