Hiskid.58 Loc: Erie, PA

OK, as it's rolling, you are correct in that the motion of the object is still taking place. Because the shutter isn't open the whole time, you don't get the "ghosts" associated with blur. I guess you could technically say that the runners legs are a bit longer because the beginning of the capture is 1/250th of a second before the end of the capture, but you won't get the blur. These times are so minute that you can't really see them with your naked eye. With a very fast object, like a speeding car, if the whole sensor was open for the 1/250th of a second, it would cause some ghosting, or blur. Because it's not all being exposed, you don't get the ghosts with the faster shutter speeds. I hope this rambling makes some sense.

Ugly Jake Loc: Sub-Rural Vermont

When you say "freeze motion" - are you talking a tennis serve or a bullet? When practicing panning at ISO 400 and f5.8 in daylight, trying to freeze an auto at 30 MPH and blur the background, I got the WHEELS completely frozen at @1/640/sec!!! (No blur in the background, either) So, what in the real world, with real light, can't you stop?

GGiant67 Loc: Rancho Santa Margarita CA

Most of the folks here, are forgetting the effect a film/sensor plane shutter has on fast moving subjects. As the curtains move across the film or sensor, the subject is continuing to move, so there can be quite a bit of skew in the resultant image. To explain further, when the gap between the shutter/curtains is on the left side of the film or sensor, the subject is in a location, that will be different by the time the gap gets to the right side. The only type of shutter that prevents this is an Iris type (Hasselblad, for example). A flash unit will usually do the trick for you, as well, but in available light, the curtain type of shutter will distort a fast moving object.

check6 Loc: Redding, CA

the OP is exactly right. A perfect example of this is taking a picture at very high speed of an airplane propeller. Because the leading and trailing edges of the shutter are essentially creating a slit which slides across the sensor, and because the propeller is moving incredibly fast, the resulting image will make the prop look like a scimitar rather than a straight blade. Because each section of the sensor catches the blade in a slightly different position. Without a flash to stop all motion, the fast moving prop can't be stopped by even a high speed shutter.

Edit: This is your real world example. Race car wheels are fast, but not THAT fast...

evandr Loc: Tooele, Utah

I think it all boils down to one simple question – "is there enough “constant” light to properly expose each pixel sensor in 1/4000 of a sec?”

If you are trying to capture something like a bullet in flight then "Bulb" is the shutter speed you need in complete darkness with a high power flash attached to some sort of trigger that will fire it at just the right moment. If you are trying to freeze a beating or rotating object then a constant intense light would be required in conjunction with a high shutter speed. In the case of a hummingbird’s wings where you have both fast and slow moving subjects then the shutter speed is not the main consideration, it’s the speed, power, and sync position of the flash that matters the most if you want to capture the bird, freeze its wings, AND properly expose the background.

Now to answer you question directly – IF your sensor’s pixels are sensitive enough to register the available light at 1/4000 of a second then “yes” you could freeze anything; sufficient light is the key. The principle is no different than the ability to freeze a slower moving subject at slower shutter speeds (say 1/350th of a second), it simply depends on how much your subject will move during the given exposure time and whether or not the available light will be sufficient and constant during the exposure.

KG

...up to the max sync speed, such as 1/250. For shutter speeds faster than that, cameras use a trick which involves moving the second curtain before the first one finished fully opening up. That's how 1/2000, 1/4000, or 1/8000 is achieved.
Not by moving the curtains faster, but by beginning to cover the sensor with the second curtain while the first curtain is still moving.



Well, not "almost like a tiny slit", but exactly like a tiny slit. The entire sensor is never exposed at the same time if you go above your body's sync speed.

All it does is reduce the amount of light that gets onto each given photosite.

But it won't help with freezing the motion because. Or rather you would be able to freeze the motion, but you wouldn't be freezing the same point in time across the entire sensor.

Here is a video that explains how two curtains work together for high shutter speed.

http://www.diyphotography.net/understanding-flash-sync-shutter-curtains-and-high-speed-sync

Get to 1:40 in the video and disregard the part about HSS for flash.

Keeping in mind how the two curtains operate, think how would you actually freeze motion?

The top half of the sensor would be exposed to the light at a different time than the bottom half of the sensor.

So if you were to take a picture of some vertical rod moving from left to right very-very fast, you would end up with a diagonal line in your picture.

BigD Loc: The LEFT Coast

Evander you are mostly correct. The flash does not freeze anything the Shutter does. The flash is used to provide the high amount of light that is needed to properly expose the scene when the Shutter is moving so fast. Like I said in my earlier reply what is needed is a discussion on High Speed Sync and how it works. More importantly would be how to use it to say photograph an airplanes propeller and freeze that sucker perfectly straight with no visible distortion what so ever. It can be done but unless you are on the surface of the Sun you would need HHS to do it properly.

evandr Loc: Tooele, Utah

That is not entirely true, even an Iris shutter does not expose the entire surface of the sensor all at once. I'm waiting for the day that the technology is refined enough that a shield, such as the one found on a welding mask, would cover the sensor and can be made to go from passing no light to passing 100% of the light for a user preset amount of time and then back with the push of a button or maybe the sensor itself could turn on and off for a period of time set by the photographer - No shutter at all, just electronics - would be nice wouldn't it.

GGiant67 Loc: Rancho Santa Margarita CA

evandr, I like your welder mask idea, but I have to disagree with your other comment. The iris, as soon as there is a "pin hole" opening, exposes the entire surface of the film or sensor. The iris shutter is layered into the lenses. If it were right up against the film or sensor, I would agree, but it isn't.

evandr Loc: Tooele, Utah

True, but it still boils down to getting enough “even” light onto the sensor quick enough to create the frozen picture. You mention an airplane propeller; a sufficiently powerful enough flash will illuminate the blades sufficiently and instantaneously enough to freeze them with a rear curtain sync speed of 1/250th of a second but they will probably look somewhat ghosted unless you really know how to set up the camera. It’s not the intensity of the flash that matters so much as it is the duration of the flash with respect to the shutter speed and whether or not that intensity is made available to every pixel of the sensor equally. Freezing an airplane propeller is easy – don’t use a flash! You can make that propeller look like it is standing still by using a powerful flood light, a very fast shutter speed and an elevated ISO (if the plane is moving or in flight then that would be a real trick).

In any case, special equipment and procedures may be warranted to get the job done but shutter speed has nothing to do with how a pixel will register light only how much light is presented to that pixel.

evandr Loc: Tooele, Utah

Yes that is true, not knowing the internal workings of the Hasselblad I did not consider that. Thanks for the info! The question I would have is how does an Iris shutter achieve extream shutter speeds if the iris has to open, stop, and then close again; perhaps it can do it in 1/4000th of a second, I just cannot wrap my mind around it.

check6 Loc: Redding, CA

Freezing an airplane propeller is easy – don’t use a flash! You can make that propeller look like it is standing still by using a powerful flood light, a very fast shutter speed and an elevated ISO (if the plane is moving or in flight then that would be a real trick).
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I'd like to see an example of that. I can show you hundreds of examples of that prop NOT freezing, but curving, even at 1/4000. That being said, in the real world, we don't want to freeze that prop at all because it looks terrible to see a prop frozen on a plane in flight. A nice blurred disc on the other hand is very nice.

However, if I'm flying and want to freeze the prop for a picture I usually pull the mixture and raise the nose to below 60mph...that usually does the trick ;-)

ShakyShutter Loc: Arizona

The "motion stopping" ability is determined by the speed of the shutter curtain. Mechanical issues limit the speed that the curtains can travel and stop without undue vibration etc.

Humming bird wings and helicopter blades are examples where the SLR shutters start to fail in the ability to stop motion. Depending on the direction of travel of the object relative to the curtain travel the stopping ability and the distortion that results will be observed.

We're talking available light for sure. The motion stopping power of strobes and lasers is a different kettle of fish altogether.

BigD Loc: The LEFT Coast

Hey that's a cool idea it would be interesting to see if someone is thinking along those lines.

I didn't say the entire sensor is exposed though I just said that the flash ONLY provides the illumination it has nothing to do with freezing anything. I guess I will toss a quick simple High Speed Sync thing out and see if it helps or stirs the pot.

Some here have basically covered how the Shutter exposes the sensor to light when it is set to one of the faster speed. Imagine an old Credit Card Swiper (think before the mag strip was used). The thing on top was swiped from right to left over the bottom tray to make a copy of the card. Imagine the shutter opening from bottom to top and closing again like the Credit Card thing. The leading edge of the Shutter is the "first Curtain" and the trailing edge is the "second Curtain". It zips over the Sensor exposing basically a small slit starting at the bottom and moving up to the top. It does this very very fast so that the slits overlap making a continuous pass exposing the Sensor to light at "almost" the same exact time. Now there is of course some time delay but it is so small that very little difference can be seen in the different slits.

The problem here is that because the Shutter is moving so fast it is difficult for light to slip in to expose the Sensor. So to help we use a strobe or flash to increase the light levels and "allow" us to use this high Shutter Speed. The next problem is that the Shutter is moving fast, but not faster than light so the Flash has time to fire, reach its brightest point, and diminish, while the Shutter is still moving. If you set your flash to fire and then set your Shutter to 1/8000 and take a picture you will probably get a picture with what we call "banding". The flash fired one time and while the strobe was at its brightest exposed just a small slit usually in the middle of the image while the rest is black. This gives the appearance of black "bands" above the below the exposed part.

The idea here is to get the flash to fire at the same time as the Shutter exposes each slit and to do that you need High Speed Sync. Remember the Flash is fired by the camera so you need to get the camera and the Flash "in syn" so it "pulses" the Strobes light to matchup with these slits as they move from the bottom to the top of the Sensor. If you can do this then you can easily photograph objects in whatever light that are moving very fast. I have photographed a helicopter as it flew overhead using HSS and also with strobes inside the helo to light the pilots and it looked really cool with the blades dead stopped, the clouds of the night sky looking ominous, and the entire image exposed well.

You cannot use a fast Shutter if you cannot expose the Sensor period. To freeze motion requires a fast Shutter and to use that fast Shutter you need the proper amount of light. If that requires the use of a strobe you "must" know how to use HSS you cannot simply "forget about HSS for now". As I said the time differential is very very small when using a super fast shutter, so fast that it requires multiple flash pulses to accomplish it. If you can do HSS properly you can freeze almost anything clear as a bell, the question now is does your camera support HSS and do you know how to take advantage of it?

ShakyShutter Loc: Arizona

And a leaf type shutter ALWAYS opens fully before it closes.

This discussion was never about the amount of light reaching the sensor.

It's about the motion stopping power of the mechanical shutter.

Nothing to do with light. It is assumed that there is enough ambient light available to achieve a proper exposure.