Swing, Driver

[Jeff Mann]

Re: Swing, Driver

Martin - you write "To end all arguments, you need to test. It's pretty easy, construct a disk on which you draw an X, two straight lines cutting across the center. Spin that disk as you film it. It will become obvious that the camera lies since the lines on the spinning disk can't physically bend although they will appear to bend on film. Once I own a camera, I'll do it myself."

Those straight lines may seem to bend if one uses a film camera operating at a slow speed (eg. 30 frames per second). However, why should they seem to bend if a video camera also has an inbuilt shutter where every single frame is captured at 1/8000th of a second?

Jeff.

[Martin Levac]

Re: Swing, Driver

The illusion, however slight, remains. For the simple reason that it is impossible to capture the whole area of the film in the same nick of time. 1/8000th of a second is not the same nick of time. It is a period of time of a duration of 0.000125 second. During that short time, the club doesn't stop so that the complete area of the film is exposed and then start back up, it keeps moving across the focal plane as each part of the film is exposed in sequence until the whole area of the film is exposed.

I just thought of this. If we were to push the camera to the limits of the possible, we would eliminate the illusion, but we would be able to see only one single photon on film. What good that'll do.

Just to be clear on this point. The illusion isn't caused by a specific frequency such as 30 frames per second. It is caused by the shutter speed, the time it takes to expose the area of film to light such as 1/8000th of a second. To understand the difference, we could capture 30 frames per second at 1/8000th exposure time for each frame.

[JohnP]

Re: Swing, Driver

All very interesting NOT - back to the golf advice please, Jeff, don't waste your time

[Jeff Mann]

Re: Swing, Driver

Martin

You obviously are not familiar with high quality cameras. At 1/8000th of a second you can definitely freeze a fast sports action, like a clubshaft in motion. If the clubhead is moving at 100mph through the impact zone, then it is moving a distance of 0.22" in 1/8,000th of a second. That is a very small amount and it will only produce a little blurring of the clubshaft movement. It will definitely not produce clubshaft bending, if it doesn't exist.

John

I will take your advice. This is my last post on this topic.

Jeff.

[Martin Levac]

Re: Swing, Driver

I don't need to be familiar with any camera. All I need to be familiar with is the mechanism that produces the illusion. What it will definitely produce is the illusion despite anything the makers of such cameras want us to believe.

Look, you wrote it yourself. "...it is moving a distance of 0.22"" "That is a very small amount..."

It may be small enough for you but like I wrote, however slight, the illusion remains. Do you know the distortion rating of those cameras? I don't but it would be enlightening to see what the makers say about that. Go back to the test I proposed to determine the distortion rating. Perhaps there is no such thing, well that's not up to me but the test will give us a good start. I've had this discussion in the past several times it's always ended with the other persons coming up short.

A distortion rating would help us in discussions where one person has this argument "We can barely see it but the shaft bends this way." Ok so it does appear to bend but barely. "Barely" in my mind count be accounted for by the camera's quality. We'd compare this bend to the distortion rating, if the bend is within the distortion rating, we discount it. If the bend is greater than the distortion rating, we accept it but write it with a +/-(distortion rating) relative to the speed of the object. We must also take into account the direction of the distortion because the illusion appears to bend the objects in different directions depending on the direction the object is moving and the direction the shutter is moving.

You see, the argument that would make the grade is something like this. "The object has been captured in its entirety on the whole area of the film in the same infinite slice of time thereby eliminating the illusion that is so common in cameras." Well, until then, the illusion remains. And to tell you the truth, I can't do a thing about it.

And that brings me back to the crux of the matter: The camera always lies. That's pretty much the only thing we can guarantee about any camera.

[Martin Levac]

Re: Swing, Driver

Jeff Mann,

You wrote that there was only one frame in which the ball was present, that is not entirely true. Look at the next frame, you can barely see the ball because it blends with one tree in the background. Go back to what I wrote about the many ways the camera lies, where it says depth of field. In the first frame, it appears that the ball shoots off extremely to the right, but combined with the next frame it looks much different.

In the first frame, the ball appears closer than it really is. The next frame clears things up.

[BrianW]

Re: Swing, Driver

Hey Martin,

I think this thread has run it's course. Maybe we have all learned something from it, I hope that goes for you as well as us.

[Martin Levac]

Re: Swing, Driver

BrianW,

I don't want to tell you you're wrong there but I must. A thread has run its course when nobody posts in it, not when somebody makes a decree unless it's the moderator and he locks it. But that usually happens because it's run up against a wall, the wall of acceptable. Wait a year, then post again saying that the thread has run its course and I'll reply the same thing I'm replying right now.

But back to the last post I made before this one, if you can view youtube videos frame by frame, try to find the ball in the next frame like I pointed out.

[BrianW]

Re: Swing, Driver

BrianW,

I don't want to tell you you're wrong there but I must. A thread has run its course when nobody posts in it, not when somebody makes a decree unless it's the moderator and he locks it. But that usually happens because it's run up against a wall, the wall of acceptable. Wait a year, then post again saying that the thread has run its course and I'll reply the same thing I'm replying right now.

But back to the last post I made before this one, if you can view youtube videos frame by frame, try to find the ball in the next frame like I pointed out.

OK Martin, whatever. You can keep posting to yourself, I am out of here Yawn!!