Is this Stroke Crooked … or is it Camera Parallax?

dr_dave

dr_dave

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Bob Jewett

Bob Jewett

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dr_dave said:
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Check out the new video. The results might surprise you. The video also includes a good example jump shot from Corey Deuel.

Enjoy,
Dave
Click to expand...
But if the camera is level and centered in the vertical plane of the shot, doesn't the cue have to remain on the vertical center-line of the image for a straight stroke? It seems to me that the camera has to be to one side of the shot to get the "straight-but-looks-crooked" effect.

Also, if the stroke is straight but looks crooked due to camera position, a different camera position should show the stroke bending with the opposite curvature (left-to-right going forward vs. right-to-left).
 
dr_dave

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Bob Jewett said:
dr_dave said:
...
Check out the new video. The results might surprise you. The video also includes a good example jump shot from Corey Deuel.
Click to expand...
But if the camera is level and centered in the vertical plane of the shot, doesn't the cue have to remain on the vertical center-line of the image for a straight stroke?
Click to expand...
Yes. Unfortunately, it is extremely difficult to get the camera aligned perfectly straight, and it wasn't perfectly straight for the shots in the video. Also, when the camera is close to the table like we had it, the effect seems to be exaggerated.

Bob Jewett said:
It seems to me that the camera has to be to one side of the shot to get the "straight-but-looks-crooked" effect.
Click to expand...
Agreed.

Bob Jewett said:
Also, if the stroke is straight but looks crooked due to camera position, a different camera position should show the stroke bending with the opposite curvature (left-to-right going forward vs. right-to-left).
Click to expand...
Agreed. I wish I had included this in the video. Where were you when I needed you? ;)

I'm heading down to the basement right now to check it out; although, I probably won't post a follow-up to the follow-up.

Regards,
Dave
 
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Snooker Theory

Snooker Theory

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Dave, quick question, hope you don't mind on a different topic but still vaguely in the ballpark.

Snooker players use their chest and chin as points of contact, although due* to the taper of the cue, wouldn't the shaft/tip be forced to the left(for a right-handed player) as the thicker park of the butt pushes against the chest in the stroke?
 
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dr_dave

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Snooker Theory said:
Dave, quick question, hope you don't mind on a different topic but still vaguely in the ballpark.

Snooker players use their chest and chin as points of contact, although do to the taper of the cue, wouldn't the shaft/tip be forced to the left(for a right-handed player) as the thicker park of the butt pushes against the chest in the stroke?
Click to expand...
Good point. Although, isn't most of the taper in front of the chest contact point? And doesn't the chest contact the cue more on the top than on the side?

Regardless, as long as the pressure on the chest is maintained, the cue will still return to the same place on the CB as in the "set" position (as with a pendulum stroke).

Regards,
Dave
 
dr_dave

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garczar said:
Looks crooked to me. Looks like some "swoop" goin on.
Click to expand...
All of the shots in this video "look" crooked, including Corey's jump shot. That's how optical illusions work. They mislead you into thinking something that is not true.

Regards,
Dave
 
dr_dave

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dr_dave said:
All of the shots in this video "look" crooked, including Corey's jump shot. That's how optical illusions work. They mislead you into thinking something that is not true.
Click to expand...
FYI to those interested, in response to a point raised by somebody on YouTube, I just added the following NOTE to the bottom of the YouTube video description:

"Samm's stroke looks more crooked than mine in the video for two reasons. The camera angle was slightly different (at a larger angle) with her shot. And as I pointed out in the video, her arm is shorter, which increases the up and down motion (and parallax effect) for a given stroke length."

Regards,
Dave
 
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garczar

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Are you using a cell-phone camera on these vids? Reason i ask is about the only time you encounter camera parallax is when you have a separate lens and viewfinder. You don't have it in SLR-style thru-the-lens cameras.
 
dr_dave

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garczar said:
Are you using a cell-phone camera on these vids?
Click to expand...
No. I am using a nice Canon camcorder with a zoom lens.

garczar said:
Reason i ask is about the only time you encounter camera parallax is when you have a separate lens and viewfinder. You don't have it in SLR-style thru-the-lens cameras.
Click to expand...
I'm not a photography guy, so maybe I am using the wrong terminology? Whatever it is, the effect is obvious in all of the examples in the video.

What would you call it besides "parallax" ... maybe "perspective projection" effect?

Regards,
Dave
 
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garczar

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dr_dave said:
No. I am using a nice Canon camcorder with a zoom lens.

I'm not a photography guy, so maybe I am using the wrong terminology? Whatever it is, the effect is obvious in all of the examples in the video.

What would you call it besides "parallax" ... maybe "perspective projection" effect?

Regards,
Dave
Click to expand...
To be honest, on your shot the camera alignment looked much better than on Samm's which looked a tad offset to me.
 
dr_dave

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garczar said:
To be honest, on your shot the camera alignment looked much better than on Samm's which looked a tad offset to me.
Click to expand...
Agreed. I should have been more careful with this. That's why I added the following NOTE to the bottom of the YouTube video description:

"Samm's stroke looks more crooked than mine in the video for two reasons. The camera angle was slightly different (at a larger angle) with her shot. And as I pointed out in the video, her arm is shorter, which increases the up and down motion (and parallax effect) for a given stroke length."

Regards,
Dave
 
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garczar

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dr_dave said:
Agreed. I should have been more careful with this. That's why I added the following NOTE to the bottom of the YouTube video description:

"Samm's stroke looks more crooked than mine in the video for two reasons. The camera angle was slightly different (at a larger angle) with her shot. And as I pointed out in the video, her arm is shorter, which increases the up and down motion (and parallax effect) for a given stroke length."

Regards,
Dave
Click to expand...
BTW, your stroke is waaay straighter than mine right now. My tip sometimes looks like the end of a divining-rod huntin' water. ;)
 
B

bbb

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i havent read all thereplies
but isnt this another version of vision center effects ?
dr dave
your response appreciated
 
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SouthernDraw

SouthernDraw

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Another interesting thread!!
I agree, the camera parallax is causing the stroke to look crooked.

But, if you would like to check the straightness of your stoke, try this. You can place use a laser level to place direct straight line between cueball and object ball from one corner pocket to the diagonal corner pocket. Placing the camera, centered side to side and up to down on the shot. But from behind the cueball. Then, use the laser level on the "up-down" mode, showing a vertical laser line centered on the shot. Then shoot the draw shot. The video should show the laser line should split your shoulder & humerus and show how straight you stroke is.

BTW, I believe that Dr Dave would not show a completely straight stroke. Just like my stroke! We both have the stroke shoulder heavily outside of the shot line. And we have a more squared up shot. To accomplish a completely straight stroke, in this stance takes some side movement somewhere. Due to your joints and body alignment.

IMO, the straight and in-line movement needs to be during the time of the strike on the cueball.
 
dr_dave

dr_dave

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bbb said:
i havent read all thereplies
but isnt this another version of vision center effects ?
dr dave
your response appreciated
Click to expand...
Good point. When your head is not in your personally vision center position, parallax does result in shot-line visualization errors.

Regards,
Dave
 
dr_dave

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SouthernDraw said:
Another interesting thread!!
Click to expand...
Thank you.

SouthernDraw said:
I agree, the camera parallax is causing the stroke to look crooked.
Click to expand...
It might not be the only cause, but it is certainly a large factor.

SouthernDraw said:
But, if you would like to check the straightness of your stoke, try this. You can place use a laser level to place direct straight line between cueball and object ball from one corner pocket to the diagonal corner pocket. Placing the camera, centered side to side and up to down on the shot. But from behind the cueball. Then, use the laser level on the "up-down" mode, showing a vertical laser line centered on the shot. Then shoot the draw shot. The video should show the laser line should split your shoulder & humerus and show how straight you stroke is.
Click to expand...
Good idea.

SouthernDraw said:
BTW, I believe that Dr Dave would not show a completely straight stroke. Just like my stroke! We both have the stroke shoulder heavily outside of the shot line. And we have a more squared up shot. To accomplish a completely straight stroke, in this stance takes some side movement somewhere. Due to your joints and body alignment.
Click to expand...
The forearm does need to be in the plane of the shot for a straight stroke, but the upper arm and shoulder do not need to be in the plane. FYI, I discuss and demonstrate this in my stroke video. Check it out.

SouthernDraw said:
IMO, the straight and in-line movement needs to be during the time of the strike on the cueball.
Click to expand...
Agreed. The cue only needs to be pointing in the right direction at the brief moment of tip contact. Having a straight stroke can help with this, especially if you don’t align with your tip close to the CB.

Regards,
Dave
 
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