Xanthoria polycarpa

x20 Xanthoria parietina

Here's a picture taken with my phone through one of the eyepieces of my 'new' secondhand Seben stereomicroscope (an absolute bargain at £64). I think this is going to increase my enjoyment of natural history by a considerable margin. Looking through both eyepieces gives an almost hyper-real image of what you're looking at. Even the kids ("God Dad, you're such a nerdy loser!") have been "wow"ing and "ooo"ing. 
The first thing I looked at was a hawthorn twig (like this one) with Xanthoria polycarpa on it. I'd picked it up on a walk several weeks earlier. Imagine, therefore, my surprise when a tiny insect appeared from beneath the foliose 'leaves' of the lichen and scurried off-field! I have no idea what it was, but when I later viewed an even older specimen of 'King Alfred's cake' fungus there were loads of them (I'm pretty sure they're the same species) crawling all over it. It came with x10 and x20 eyepieces and the object lenses are in a turret which can be rotated from x2 to x4. To be honest, x20 is all I've really bothered with so far.
It's widely found on twigs, especially elder (Sambucus nigra). In full sun it is incredibly bright yellow. In shadier areas it's more greeny-yellow. In the photo you can see the fruiting bodies (the cup-shaped things with darker yellow centres) which contain the spores.