Just messin...

For those of you in the know, you'll instantly recognise the...( er, I've just realised I don't actually know what it's called. Good job I have no shame or that could've been really embarrassing!)
This bit of my French Horn is part of the valve on the underside of the instrument. I'm still just messing around with the macro setting on M's point and press. Must get a camera of my own... Looking at canon D-SLR or similar. Good idea?