A question about slow shutter panning.

I was taking some shots of classic cars this week, and was using slow shutter speed to capture motion blur in the background and wheels. A lot of my shots came out like the one below: sharp at the back end of the car, but blurry at the front. I was using high (11+) f-stops, so depth of field couldn't be the issue (and it obviously looks like horizontal motion blur). I was set for back-button focusing and pre-focused on the spot where I'd get a side view, then waiting for cars to come by panning with them from about 100-200 feet out. What am I doing wrong and how do I correct it? The shot below was taken at 36mm, f/11, 1/125 seconds, and about 30 feet, using my T1i and kit 18-55 lens (I also took a lot of shots with my EF 70-200 f/2.8 II with the same results) which gives me a depth of field from 11.9 feet to infinity. I shot hand-held, bracing my arms at my side and turning from the waist, and also shot some tripod-mounted (I had more keepers with the tripod). How am I getting the back of the car sharp but the front is blurry? The cars were doing 40-50 mph (I could understand if they were approaching the speed of light, but...). Thanx in advance to anybody who has some insight into this problem.

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I'm an aviation photographer and haven't done much of any car photography and I see this in planes sometimes. I have noticed that panning shots that aren't a perfect profile of the plane tend to be fuzzier than those that are a perfect profile. Why that is, I don't know. It's probably just my own inexperience coming into play. Sorry I'm no help.

It's because of the angle.

Different parts of the car are travelling in different directions relative to you.

I'll try to illustrate...

<---------------<<<
*

You are the * taking a photograph of the car <---------------<<<. The < is the front of the car and the <<< is the back. The car is traveling to the left.

Now, if you look at the <, it is cutting directly across your field of view. It's moving from your right to your left. So it's going to have motion blur across the image.

But the <<< at the back of the car isn't really changing position relative to you. Sure, it's getting closer, but it's not moving left or right, and it's not moving up or down. So it's going to stay in pretty much the same part of the frame. So no motion blur, or at least, not very much motion blur.

Hope that explains it.

Thanx for the post, Tiberius47. I thought of that, but it seems as if the problem is worse when the car is closest to me (i.e., when I'm perpendicular to the car's motion). The effect should be minimal at that point, as the front and back of the car would both be moving the same, relative to me. At a distance, the car "grows" in the viewfinder, but when it gets to where I'm perpendicular to its motion, the "growth" stops, then the car begins to "shrink" in the viewfinder as it gets farther away. Or am I missing something?

It's worse when it's closer because everything is moving so much faster through your frame.

Dead-nuts-on side pans are best for getting everything on the car sharp:

IMAGE LINK: http://www.flickr.com …s/burnsyphoto/8​081319255/

IMAGE LINK: http://www.flickr.com …s/burnsyphoto/7​974809872/

IMAGE LINK: http://www.flickr.com …s/burnsyphoto/7​965195132/

Master of Defenestration wrote in post #15116021
It's worse when it's closer because everything is moving so much faster through your frame.

I'm panning with the car, so it's not moving thru the frame. It's growing in the frame as it gets closer, stops growing once I'm perpendicular to its movement, and then it shrinks in the frame as it moves away from me. When it is closest, it should have no relative motion between the front and back of the car.

ScubaDude wrote in post #15116097
I'm panning with the car, so it's not moving thru the frame. It's growing in the frame as it gets closer, stops growing once I'm perpendicular to its movement, and then it shrinks in the frame as it moves away from me. When it is closest, it should have no relative motion between the front and back of the car.

Due to geometry, differing parts of the car get larger/smaller within your frame (what I meant by "move") at different rates, causing the blur to be different. The further away from your focal point, the more it's going to blur.

Sorry, that's the best I can explain it (as it works in my head)...I don't have the vocabulary to go much further than that

It's the laws of physics at work and there's nothing you can do about it.
It's called the parrallax effect.
This link has diagrams and is the best explanation I've seen anywhere...
https://photography-on-the.net/forum/showthre​ad.php?t=487139

ScubaDude wrote in post #15115996
Thanx for the post, Tiberius47. I thought of that, but it seems as if the problem is worse when the car is closest to me (i.e., when I'm perpendicular to the car's motion). The effect should be minimal at that point, as the front and back of the car would both be moving the same, relative to me. At a distance, the car "grows" in the viewfinder, but when it gets to where I'm perpendicular to its motion, the "growth" stops, then the car begins to "shrink" in the viewfinder as it gets farther away. Or am I missing something?

It's growth may stop, but that's when it's travelling the fastest across your field of vision.

In the example image you psoted, you'll notice that the front of the car where the effect is greatest is right in front of you and moving across your field of vision the most, where the back of the car - where the effect is least - is still moving somewhat towards you.

Also bear in mind that the effect can be accentuated because you are moving the camera as well. If the camera is panning at the same speed as part of the car, then that part of the car will be stationary in the frame and thus won't have motion blur. But since different parts of the car are moving across the frame at different rates, some other parts of the car may be blurred.

I;d say that it is a combination of these factors that has lead to the blur in your example. The camera was panning at the same rate as the rear of the car. But because the front of the car was moving across the frame faster than the rear, there was some blurring.

Next time I'll set up further back from the street and use a longer lens. Shallower angle between the front of the car and the back should reduce the effect.

yeah, that should do it.

As others have said using a wide (ish) lens with a 3/4 pan can create some interesting photos. Canon 7D 17-85mm at 17mm 1/60 spot focus.