Thing with the 8400 is that it's a great little camera but only up to a point.
Try to use it above ISO 100 and it gets really noisy. It also gets a fair bit of purple fringing on longer exposure shots.
Basically the sensor can't compete with that in a decent DSLR. In fairness you wouldn't expect it to, it's a 6 year old camera and a pretty small sensor.
Edd - do you use manual or auto focus for your underground shots? I've always found it so tricky to focus manually in the dark. Easy on close up objects, anything where you can clearly see the subject, but massively difficult in large chambers (even with 2,000+ lumens to play with).
That's one area where the 8400 scores, that 'manual' focus wheel - lock it off on infinity and at F2.8 pretty much anything over a metre away is in focus :)
But I guess the 8400 has had it's day and the future is DSLR or Four Thirds. I'm getting
better results from my Lumix GF1. Now I'm trusting it to auto focus...
my orders are to sit here and watch the world go by