I shot Indycars for 6-7 years back in the early 1990's.
I learned to shoot at about 1/30th or less (for artsy shots) with reeeeeeeally steady motion, without regard for aperture, to 1/200th (juuuust that little bit of motion or when they're at full song) with the smallest apertue I could get by with. On one occasion the sun was perfect but my backdrop had a trackside porto-san in it: I shot f2.8 with ND filters to slow my shutter, and blurred it away.
The difference in blur, front to back, is caused by your panning actions themselves. The kart looks like it's on a straight, and you are panning, right to left. The camera is turning, the car isn't, and something's gotta give - in that case it's the front of the cart. Additionally, you might be moving your body withut knowing it - that causes all manner of things like up and down blur in odd places. Maybe you took an involuntary breath. Photogaphers move a LOT when panning shooting race cars.
Tip: shooting from the apex of a corner and panning gives really smooth results - you're turning, the car's turning, life is good. I always did better with a longer lens from a distance - I could control my body rotation more.
Incidentally - that shot is quite good - go look at RACER or Road and Track and check their action/blur shots - this pic, if it was Hamilton, Andretti, or Tracy could keep up with the big boys and make a sale...too bad the sun wasn't out, though.
I sold the one below to On Track magazine in 1992 or 93 - shutter was something like 1/30 - it was the title shot for the article on Kim Green's racing team.
Not a great scan, and not a particularly good shot, but see the difference in blur from the front to back tires? He went by me at an angle, about 90MPH, headed uphill to pit. Wierd angle to pan, and in the end I love the effect. The reason they liked the shot was because I missed my subject: I was shooting for Jaques' distinctive helmet, but his dad's car number (27) came in focus - the editor liked that. Funny how that works.
And the trick, when they're moving at 185 to 225 mph is similar to what Village said: start tracking early, as soon as you can, and (depending on shutter lag - cars could go 10-15 feet or so with my old film cameras) release the shutter just before the feature you're shooting for (helmet, for open wheels, driver or rider body for karts and bikes, sponsor name if you're on assignment) gets there. Keep the center focus on the feature, do NOT autofocus (nice thing about racing: they go by almost the same way every time. Lots of setup time available). Crop later.
And Double H - I shot NHRA twice and didn't sell a thing: drag racing was HARD to shoot! Your shots are lovely!
That's what I was looking for! Thanks, i just didn't know how to explain it because I really didn't know exactly what "it" was. Just that it was some technique I wasn't grasping. The whole part about matching my camera swing with the apex makes SO much sense. The camera is coming around the same radius as the subject -->) ). Where I was on the out side of the turn counter acting the subject -->) (<--- which is what I was doing. HUGE discovery/lesson for me today. :hail:
I expect to see much better results next time Im out.
You suggest not using auto focus? Even though AI Servo (canon) tracks the subject... the whole mathematical algorithm deal that can calculate where the camera needs to be focused at the point the shutter releases. I would think I would do a lot worse with manual focus. That and would only get one chance per turn to get a shot (where as using AI I am shooting at the cameras 8.5fps and can get over 15 chances of getting one) Explain further if you could. You've been of great help comprehension wise thus far. Really appreciate it.
As for the shutter speed matching the focal length, I have heard that as well. I use that more for when Im trying to push a low light situation so as not to get camera shake but still get all the light I can get with the longest shutter speed possible. Where as here I want to get that overly exaggerated blur in the background and just shoot lots of shots and luck into a few spot on pans every now and then. Matching the shutter speed seems to get more blur like of the Drag shots above. I'm looking to get a disgusting amout of motion blur