im just in the process of putting together a little photo shwing all the shots i used so you can see what i used and how i got the end result kind of thing
the process i use is take a normal exposure of the car, then when i was using my strobe light took between 8-12 photos with the light in differnet positions to light the car camera was set at f8 1/160 this is kind of a bit of trial and error so you get the right amount of light just from the strobe and then took a slightly underexposed shot for the sky, you could use some grad filters for this as that would also help really bring out the detail in teh sky and means alot less playing in ps to tweak the sky
in photo shot its just a case of lining up the photos (i need to get a shutter release for my 50d as everytime i press the shutter the camera has some very slight movement ) i have found that using the 'lighten' mode for the layers with the light on work well and just shows the lightpainted areas of the car
then its just playing with levels / saturation/ curves / brightness +contrast / sharpening, i tend to play with the shadow/highlight adjustment for the clouds and bg
hope this give a bit of an insight to what i do normally takes about a hour or so to edit one phot like this
