Is it a DS? I'm hopeless with Citroens, except the 2CV. The owners were having a midnight party on the beach, so I had to work quickly before they came back: I'm not sure how I'd have explained an Englishman lying under their car in the middle of the night with a flashgun! It's a 3-minute exposure taken on a 5D, and the colour was added with an ancient Miranda flashgun and some coloured filters that I got in 1986! I keep it in the botom of the camera bag for this sort of caper. I think the car is slightly underexposed, but it was pretty much a 'grab and go' situation. 5D mk1? It's a cracking shot if it hasn't been edited at all. Did you shoot RAW or jpeg? If it's a raw file you will be able to delve deeply into the shadows and bring them up without loosing to much IQ. Or get some layers going on in Photoshop. Using a curves adjustment layer you can make those star trails pop out. Then mask the rest of the image. Do the same with the car too.