Here is an unripe fruit of the hawthorn (Crataegus monogyna) tree. This one is about 12 mm in diameter. Right click for full resolution. The ripe fruit is edible and is said to taste of over-ripe apples.
Equipment used: Canon EOS Rebel T5i with a standard zoom lens (EF-S 18-55 mm) on a 7 mm long extension tube.