Motion blur

AJQS

AJQS

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Name
Alan
Edit My Images
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Ok so you have something that's moving horizontally through your shot, and you shoot it a little too slowly, why is it that there's more motion blur the closer it is to the edge of the frame with the centre looking sharp? :thinking:
 
I'm going to go with the focal length changing?
Even though it may be moving horizontally, the focal length will change as it goes past you, unless it is going in an arc of course. Imagine having a piece of string attached to the subject, if it is moving in a straight line the string will start tight, go slack then tight again as it passes you.

Of course I may be totally wrong, it's happened before, ask my wife :)
 
Are you talking about there being more motion blur right at the edges of the image ie. background bluring, or the edges of the object your taking the photo of?
 
It's always the leading edge of a moving object, actually seems to matter not it's position in the frame, more the distance from camera, but why should it matter if the entire object is moving at the same rate?

For example:


Through the Meirionydd Autumn by Richard A. Jones, on Flickr

Leading smokebox is blurred, cab is less blurred, downhill end is a tiniy bit blurred, but the remainder of the train is sharp. (as sharp as you can get at a totally unsuitable aperture like that, what was I thinking!:bang:)
 
I'm not 100% sure from that photo but is it just the loco that's blurred or are the surroundings blurred too? If it's the latter then it's probably not motion blur but just differential focus.
 
Nope we're talking exclusevely about motion blur, this is not a 'Wh yis my photo soft/blurred?' thread, it's wondering why motion blur isn't consistent along the entire moving object.
 
A lot of the time it depends on how far the camera is from the object you are photographing. If something is moving left right perfectly parallel to the lens then generally the whole object will be blurred. Unless it's quite close to the lens...

But, for your train example, the front of the train is closer to your camera than the rest. So if you move your camera to track the middle of the train the front will be slightly blurred. If you track the front, the back will be slightly blurred. I could draw diagrams to show you why, but let's see if I can explain...

If you got someone to stand 10 meters from your camera and bounce a ball up and down think how far you'd have to move the camera to track it. Not much really. Now get them to stand a meter away and do the same thing. You'd have to move your camera a lot more. Next, think of them throwing that ball at you and over your head so and you have to keep tracking the ball. As it get's closer to you you would have to start move the camera faster to keep tracking the ball.

Well, this also happens for long moving objects, like the train for example. You don't have to move your camera as much to track the back of the object in comparison to the front if it is somewhat moving towards you. It kind of happens at a greater scale if the object is quite close and moving parallel to the camera. If you track the dead centre of the object, e.g. a car, it's quite possible that the front and rear or it will have motion blur but the centre will be almost perfectly in focus.

... if that makes sense...
 
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