Motorsport Question

[Chicken Chaser]

I've seen some shots whereby the front of the vehicle (car or bike is sharp as a tack and yet the rear of it has motion blur. Not just DOF, but actual blur and wondered how you achieved this? Is it to do with the angle of the shot and thus you're following the front while the back is doing its own thing along another parallel or is it to do with the speed of camera movement?

[A Curtis]

Combo of the shutter speed and the direction of the car as far as I'm aware.

If you shoot a car perfectly side on, it's 99% of the time going to be the same as each end like this;



With a slow shutter speed and changes of direction is where you get the odd mix;





From my experience anyways, I'm someone more 'in the know' will be along shortly.

[covboy]

You get more of this “effect” with shorter focal length lenses (plus slowish shutter speeds)

Best way I can describe it is, if you pan with the car and follow the (say) the centre of the car, the front end and back end are travelling across the camera plane at different relative speeds hence giving the blur effect.

The longer focal lengths give a “flater” plane and less swing on the pan

Edited by covboy on Monday 9th May 12:29

[Chicken Chaser]

Ahh I understand. I'd have to be fairly close to get a decent shot with a short focal length when it comes to shooting bikes. I guess I'll have to look for the shots where the back end is travelling in a different direction to the front!

[Cybertronian]

I recently pondered about this very question. Would increasing depth of field, say shooting at f/16 to f/22, improve things so long as there was enough light to maintain the shutter speeds?

[covboy]

Cybertronian said:

I recently pondered about this very question. Would increasing depth of field, say shooting at f/16 to f/22, improve things so long as there was enough light to maintain the shutter speeds?

Not sure what you mean by “improve things”

It’s not and aspect of focusing that produces the effect. As I said it’s down to the difference in relative speeds of the subject across the film/sensor plane..

[tim-b]

This effect is determined by the difference in the angle of the car to the viewer, from the time the shutter opens to the time it closes. So when a car drives past you, you will first see the front, then front and side, then side, then side and rear, then rear. So relative to you, the car is rotating (as well as getting closer then further away), and by aiming at a part of the car you can keep it relatively sharp while the rest of it is 'spinning around' that point.

Being closer to the car will increase this 'rotating' effect, and being further away will reduce it (imagine a car driving in the distance, it's angle relative to you hardly changes). However, shooting from the centre of a constant radius corner will make it possible to be close and keep the whole car sharp, as relative to you it isn't appearing to rotate - making big background-only blurs possible. Druids at Brands Hatch is a great location for this!


IMG_3588 by motion_captured, on Flickr

[Gemm]

Here's a comparison for you; same location & focal length but with different shutter speed.
1/160s


1/30s

[mattdaniels]

Chicken Chaser said:

Is it to do with the angle of the shot

Yes.

[Chicken Chaser]

Thanks for the examples etc folks, will give it a go tomorrow.