Shutter; how fast for moving objects for sharp pic?

Still testing my new 70-200 f4L; I shot my daughter yesterday on a rope swing and the photo is horrible. It is so blurry that it is useless. I don't think it was the lens. Here were my shot details:

shutter: 1/640
f4
ISO 100
focal length 200.

Sorry, I can't post the photo from here....but just looking at that metadata, was my shutter just too slow for a swinging child coming at me?

thanks,
daniel

Suggestion: Crank up your ISO as far as it will go, and then back off one notch. Now see what kind of exposure solution your camera will do in sports mode. The shutter speed should be significantly faster than what you were trying.

Also think about depth of field. If you are shooting your daughter on a rope swing, then either you are on the side or else in front. If you are in front, then she is swinging in and out of the optimal focus, so you have to widen the depth of field significantly (which means smaller aperture, which means slower shutter, which is not what you want). If you are shooting from the side, then she is swinging along a constant plane of focus (which means you can get by with a small aperture, which means a faster shutter, which is what you want).

On the other hand, if you are in front and she is swinging toward you, then her apparent motion blur will be behind her and not so visible, but then you are back into the quandry above.

---Bob Gross---

Isn't it true that the fastest shutter speed is actually 1/200? This is shortest time at which the first curtain is fully open before the second curtain starts to close. If so, then any 'faster' shutter speed is really only a 'window' which moves acroos the focal plane, with the window being more narrow as the shuter speed is reduced.

This might cause blurring of an object that is moving quickly towards the camera, as different parts of the image would be exposed at different times (and in varying degrees of focus).

???

boB

No, it does not cause blurring.

A focal plane shutter can go to 1/4000 on some cameras. No problem. No blur.

Don't be confused by the maximum sync speed for flash units, which is typically like 1/200. You can go faster than that, but only with a flash unit that supports high speed sync mode.

---Bob Gross---

Hmm? Interesting question. I don't know if the fastest actual shutter speed is 1/200. I certainly would have thought that it was actually the speed that is available.

Yeah, Robert, that is what I would have thought. I know the flash sync with the built in flash on the rebel won't let the shutter go faster than 1/200

A good rule of thumb for longer glass is 1/focal length to stop action.
Faster for faster subjects or to help freeze all motion.
In some situations cranking it up to 1/1000 to 1/1600 is possible.
Doing so not only stops action, but keeps camera shake from being an issue.
Depending on the usable max ISO setting of your camera, you can adjust the ISO setting faster to allow faster shutter speeds.
The fastest shutter speed comes into play when using a flash. The fastest shutter speed the flash will sync at is 1/200th. You can shoot at faster shutter speed with a flash in high speed sync mode, but usable distance is decreased for your flash.
The window theory would be true if the subject is moving towards you or away from you fast enough to move out of your focal field in the same time as the exposure. It would have to be moving extremely fast to move out of focus in say, 1/2000th of a second.

1/640th..?

That's pretty fast... but if you double the ISO you can double that shutter speed to 1/1280 or so...

With a 200mm I usually need 1/250th or so to get people in motion.. if they aren't moving to fast that is

I would also check where the focus point was in the shot. This could be a case of the focus point not being the child, but somewhere else in the image.

A few weeks ago, a helicopter flew overhead, and I shot a photo using a 200mm lens. At 1/400 shutter, the main rotor was blurred. At 1/4000 shutter, it seemed to be frozen perfectly. But I had to crank up the ISO high to get an exposure solution, even in bright sunlight. It was far enough away that there was no depth of field issue, so I could shoot wide open.

---Bob Gross---

Well, I its not an AF point problem. That is right where I intended it to be.

Is there a way to post photos on here...or do I have to provide a link to another website?

You need to upload pic to webspace then use insert image tags. You can use alt and p to insert them. the last one has to have a / in it.

After some further research, it appears the *actual* shutter speed is pretty close to the flash sync speed. This is the fastest speed at which both shutter curtains are fully open, & the fastest speed at which the curtains travel across the focal plane.

The *effective* shutter speed is faster when the slit is narrower, up to 1/4000 and less. At fast shutter speeds each pixel gets only the selected time for exposure, but the *total* exposure time still takes about 1/200 second.

High speed sync flashes fire a burst of rapid pulses to allow each burst to expose a different area of the sensor as the curtain slit travels across (or down in some cases) the focal plane.

I would have to agree that the object would have to be moving towards the camera pretty quickly to affect the focus so the shutter speed is probably not the cause in this case.


boB

not being able to upload the photo here. With the AF in the right spot, the shutter at what seems fast enough....I guess I have only to blame the new lens?

The other thought is that the DOF being set at f4 was just too shallow and she swung out of the DOF by the time I fully depressed the shutter release?

What probably did it was the lapse of time from your brain telling your finger to shoot and the shutter lag combined. It may have appeared in focus, but the actual shot was off.
You can put a link here to were you have the image posted.