Once again, thanks for the comments. They make a big difference. (especially when there's criticism too!)
@posiview:
Thanks for the writeup! I've thought about most of these things though,
1) most needles are far too small for this photo, and to get close enough for the needle to be properly visible the DOF would have been too small for much bubble to be in focus. I had a choice between a pristine pencil and a hard worn one, so I chose the pencil with more texture

. I'd definitely like to try again though and I'm pretty sure this will be my photo to re-shoot if a reshoot card ever comes out.
2) I'm not sure I understand about the sharpness. The bright light reflected in the bubble is sharp on the right hand side because it's from the outer surface of the bubble. The reflection on the left of the bubble is from the inside surface and has been blurred by the bubble itself. The contrast between bubble and background is quite low though and I agree it doesn't make the bubble look very sharp around the edges.
3) I have a picture from the instant that the bubble popped but it's very boring. This bubble mix doesn't burst in an exciting way. It just looks like half of the bubble has been photoshopped away. Here's what it looked like:
Halfway bubble by
ConicalFlask, on Flickr
@TopBanana:
Thanks!
I plan to revisit this soon with more technology (being more suited to engineering than artistry (hopefully

). I'll check out those bubble photos soon.
I found that the bubble was quite hard to see under normal lighting so added some christmas lights to paint dots on the bubble and a bright, sideways halogen (20w desklamp) that wasn't shining on the wall behind. Yep this was with my canon FD 50mm F1.4 again. It's lovely. The wall is uniform because the bright lens has such shallow DOF even at F4 (in this picture) that any details on the wall behind (about a metre away from the subject) are wiped out.
I've started work on building a configurable laser trigger so I can revisit bubble/insect/destruction photography without so much ball-ache in future. I didn't really want my hand in this photo but the bubbles only lasted ~~3 seconds and that wasn't enough time to blow, focus and click.