Capture of high speed digital images

[Clubdoctor]

Looking for some advice on how to capture digital images of golf balls, with consumer-grade still or video cameras.

The images would then be imported into a PC program to enable ball spin rates to be calculated/measured by measuring ball rotation in a fixed time-frame.

Ideally I should like to be able to measure spin rates up to 9,000 revs per minute, although the ability to measure spin rates up to 4,500-5,000 rpm would be acceptable.

Accuracy needed is plus/minus 2%.

Has anyone done this, or something similar?

If so I should be grateful for any advice.

Thanks in anticipation.

Richard Kempton

[PacAce]

Richard,

I don't pretend to be an expert at this but I imagine you would need a high speed camera to be able to do this. If I'm not mistaken, the frame rate of consumer video cameras are 30 fps (for NTSC). If you're trying to capture a spin rate of even 4,500 revs per minute, that's about 75 revs per second or 2.5 revs per frame. Since you'll have to capture a fraction of a rev on each frame to be able to acurately determine spin rate, you're going to need a lot more frames per second (e.g. 75+ fps) to be able to capture spin rates of 4,500 per minute and twice more for 9,000 revs per minute.

A high speed film movie camera might be your best bet but how to digitize the individual frames for analysis?

Good luck! I'll be curious to see how you pull this off.

Edited: Just thought of something else. A consumer video camera might be doable in conjunction with the use of a multi-strobing strobe light in a darkened room or outdoors at night. If the strobe is set to, say, 80 or 90 strobes per second, you should be able to capture the rotation of the golf ball as it flies through the air. (I'm assuming you'll have a reference point on the ball, of course.)

[Clubdoctor]

PacAce

Thanks for the reply.

I think I've figured out a way to do it with a digital still camera and a high-speed (i.e. short duration flash).

What I need is a way of triggering the flash to capture the golf ball as it passes in front of the camera lens. Shutter will need to be open when the flash fires, but I think that a shutter speed of about one-tenth of a second will achieve that for all ball velocities (see below).

Any ideas on suitable triggering devices & likely costs?

The camera will be about 2 feet ahead of the stationary golf ball.

BTW, I only need to capture spinrates up to about 4,000-4,500 rpm (the maximum that can be achieved with a driver). Ball velocity will range from about 6,000 ft/sec to 14,000 ft/sec.

Thanks and regards

Richard Kempton

Sorry - the above velocities are in feet PER MINUTE, not per second

[PacAce]

Richard,

When you say that you need to trigger the flash as the ball passes in front of the camera, I'm assuming that you're talking about firing the flash just once, correct? This might be a problem as I do not see how you can measure a spin rate of a ball with only one instantaneous photo of a ball.

However, if you use a strobing flash, you might be able to accomplish what you want. You'd have to set the strobing flash to fire multiple times for a given duration (just long enough for the ball to pass in front of the camera and beyond). If the strobe can't be set to turn off by itself, then an assistant should be able to turn it off at the appropriate time.

Once the strobe is set for the correct flashes per second (enough to capture the ball's spin rate), you can have it triggered by a sound detector, much like how the "clap on, clap off" light switch works, as soon as the club strikes the ball. On second thought, maybe you won't even need to trigger the strobe. Your assistant can just turn it on when you're just about ready to hit the ball. You can get a variable rate strobe light from Radio Shack.

You'd have to set the camera back far enough to be able to capture more than 1 rev of the ball's spin in the frame. The final photo should show multiple instances of the golf in mid flight. For you to acturately gauge the spin rate, you will need to set the flash stobe rate precisely since that's what you're going to use as your time base. Sorry, but I can't offer any suggestions on how to do that short of you buying a strobe unit with an acurately marked dial.

Since I've never really done this myself, what I'm suggesting is just "theory" stuff.

[Clubdoctor]

PaceAce:

I hear what you're saying, but I really do only need ONE photograph, because I've got a way of working out the spinrate by another route (that's the clever bit and since it might be patentable, I'm keeping stumm about it for now). I still need an image of the golf ball about 2 ft from it's starting point.

Strobing is no good, because of the need to have people hit the ball in darkened conditions (which is difficult for some people) and I'm concerned at what might happen if one of my customers turns out to have epilepsy and the strobe triggers an attack.

So - is there a way of triggering the flash as I described above? Any ideas on cost?

Thanks & regards

Richard Kempton

[PacAce]

Richard,

Sorry, but I've run out of ideas on how to do what you want short of writing a little computer program that picks up the sound of club striking the ball (via an attached microphone), waiting a desired number of milli seconds and then having the computer monitor, which is at first blacked out, turn white. This transition of the screen from black to white will be picked up by a light sensor that triggers the flash. The light sensor shouldn't cost more than a few dollars. I built one many years ago to trigger a slave flash from the main flash using a photo transister which I bought from Radio Shack.

Only problem is, how are you going to release the shutter on the camera?


Here's something I found on the internet that might be of interest to you:

http://www.outdoorphotographer.com/content/pastissues/1998/dec/head.html

[Ken Fong]

Not sure if this applies, but the Nikon F100 has a 'trap focus' feature, where the camera (not you) will trigger the exposure when an object comes into a predetermined focus point. My friend does a lot of formula racecar photography and finds it useful for that purpose. I have no idea if Nikon has kept that feature on any of their digital SLRs.

Someone found a way to do it with a Canon EOS 1D/1Ds:

http://forums.dpreview.com/forums/read.asp?forum=1019&message=4401362

[Clubdoctor]

Thanks for the suggestion re. the Nikon.

Would it react fast enough to a golfball moving across the lens at about 235 feet per second?

I know I suggested that strobing was out, but has anyone any experience or opinions on the Canon 550Ex Strobe Flash & how that might be adapted to achieve what I'm trying to do?

Richard Kempton

[Ken Fong]

My guess is that it would still be blurry without a real professional setup. There might be some students at MIT that are continuing Edgerton's work but with more modern devices...they might even do it for you.

http://www-caes.mit.edu/research/edgerton/screen01_welcome.html

http://mitpress.mit.edu/bookstore/authors/edgerton.html

[olizim]

Hi Richard, Everyone...

Just curious if someone has solved this problem...I'm setting up a "driving cage" in my back yard and would like to connect me Canon D30 to a strobe and computer and figure out what the damn ball is doing...

I though an "electric eye" just in front of the ball would work to trigger the strobe...and that 2 flashes would be required (either with 2 strobes or a strobe that can be set to strobe twice).

I guess having a suitable dark background might allow me to leave the shutter on long enough to pick up both strobes and thus have a single image to analyze.

Any thoughts ?

Oliver

[PacAce]

Hi Richard, Everyone...

Just curious if someone has solved this problem...I'm setting up a "driving cage" in my back yard and would like to connect me Canon D30 to a strobe and computer and figure out what the damn ball is doing...

I though an "electric eye" just in front of the ball would work to trigger the strobe...and that 2 flashes would be required (either with 2 strobes or a strobe that can be set to strobe twice).

I guess having a suitable dark background might allow me to leave the shutter on long enough to pick up both strobes and thus have a single image to analyze.

Any thoughts ?

Oliver

Just out of curiosity, what did you have in mind as far as the ball is concerned? Did you just want to see it being hit by the club (I'm assuming you're talking golf?) and taking off a split second later or did you want to see the whole trajectory of the ball from beginning to end?

[gjl711]

Light triggers are easy to make and you can get all the parts at your local Radio Shack. See:
http://swannman.wordpress.com/2006/08/24/howto-build-a-flash-trigger/

Then you can adjust the trigger wherever you want. But there is even an easier way using the same circuit. The 555 timer is a great little chip capable of delivering very short and consistent timing pulses. With the light circuit you still have the problem of having to have the ball pass through the trigger, but if you replace the light sensor with a simple switch, one blade being placed right behind the ball, and the other blade on the face of the club you have a perfect trigger. As soon as the club face touches the ball, it triggers the 555 and with a simple adjustment of the cap/resistor ratio, you can set the delay to anything you want from micro-seconds to hours.

[gjl711]

I found a much better web site. Take a look here (http://www.doctronics.co.uk/555.htm). The one your interested in is the monostable circuit, but there are other others that would work well for multiple pulses as well. Also, it would be trivial to replace the light trigger with a small pizo-electric mic and trigger off of sound.

[bubba22]

Any new inFormation on this? Looking to use 3 Firefly MV cams from Point Grey at 122 fps with 30 us shutter speed. Plan is to trigger each cam 2 us apart and use a ir flash with each to get 1 image from each cam to allow measurement of spin. Any suggestions?

[PhotosGuy]

Strobing is no good, because of the need to have people hit the ball in darkened conditions (which is difficult for some people) They don't need to hit the ball in the dark. It just needs to be in the dark when you photograph it.
Harold Edgerton (http://web.mit.edu/Edgerton/) was stopping time decades ago with specialized cameras and lighting.

Simple strobe and sound trigger setup, (http://www.diyphotography.net/great-high-speed-photography-trigger-by-tom-barnett)

mORE: http://www.hiviz.com/tools/triggers/triggers2.htm

high speed camera. (http://www.photron.com/)

[bubba22]

Here is the cam I will be using http://www.ptgrey.com/products/fireflymv/fireflymv_usb_firewire_cmos_camera.asp Any thoughts? Plan to use 3 of them and trigger in sequence. Any suggestions? Looking to capture fast golf ball at 150 mph.