Originally Posted by
Mr IGH
I don't think modern photo finish cameras use a slit, that's what they used for film cameras. Digital photo finish cameras are just high speed motion cameras running at ~2000fps. The distortion is different between the two methods, the curved spokes is a digital artifact.
When you see this kind of background (ie no background) - you know it's not a snapshot - the slit only sees one line of background and it stays the same and the horizontal axis is time, not distance.
Here's what the actual line looked like (from the other side)
