Why No longer Shutter Speeds Than 1/24, 1/30, or 1/60

I understand the limitations of film, and why you can't have shutter speeds longer than the frame rate, but since digital is here, why can you not have say 1 second exposure times in video? Couldn't they overlap? For example:

(Text spacing was removed when I posted, so I posted a screen shot, and somehow the spacing is a little off, but you should get the idea.)

It's the same with digital cameras.
If a digital camera have a frame rate at 30fps (Most common) it can not have exposure time above 1/30 and that is why so many cameras that records at 60fps need more light they must make exposure faster than 1/60. Remember that frame rate is very similar to film, the frame rate is how many times the camera rescans the CCD. However there are cameras that can have 1 sec exposure time and a frame rate at 1 fps.
This gives you nice effects (Time compression) like showing the decay of a flower in 10 seconds or rapid moving sky.
You can also do this with any digital camera (remember tripod) and then add the frames together in Pinnacle etc.

Why can't the frames overlap?

Remember that in a digital video the motion is a sequence of digital pictures. So @ 30fps the camera is taking 30 pictures every second. Thats the deffenition of fps, a new picture at the given frame rate. Every time the camera takes a new picture it must stop the exposure to collect the info(picture/frame) and store it, then it must start to take a new picture. As a thought experiment : If you at a 30 fps camera would "force" the camera to take 1 sec exposures and stretch it out over the old 30 fps, then you are in fact changing the 30 fps to 1 fps. There is not really any difference, since the definition of fps is # of frames or new exposures during a second. However since 30 fps only mean that the a new picture should be show 30 times during a second, you can have shorter exposures like 1/1000 sec.

Another thing, if you are thinking about the TV, then it changes picture every 1/60 sec (60hz) in the US, so if you are showing digital stills or videos at 1 sec fps then the exposures will be stretched out over the TV's frames (60 hz): but that is something else.

This is easier in whole numbers

I want to shoot video at 1 min, f/2.8, iso 100, but at 1fps. Lets say we start recording the first frame at 00:00. The first frame would record from 00:00 to 01:00, the next from 00:01 to 01:01, the next from 00:02 to 01:02, the next from 00:03 to 01:03, and so on.

The payback would be 1fps, the recording would be one frame per second, but the shutter speed would be 1 minute long.

My whole question is why can't you shoot digital video like that. You would just be overlapping the exposures (taking several exposures at once, but each one would have a different start and end time). The sensor would just constantly be recording and sorting out the information to the respected frame.

In film, you can't do that because each frame has a physical start and end, but that isn't the case with digital.

adam8080 wrote in post #7639652
In film, you can't do that because each frame has a physical start and end, but that isn't the case with digital.

But remember what "shutter speed" is on a CCD, it is a new reading of the CCD brick because it's a new picture.

If you turn on a digital camera for one minute and makes a recording at 1 fps. The CCD brick is read every second.
the CCD is one for a minute, however every time the CCD is being read, the system needs to gather light all over.

A CCD is an array of small battery like condensers when light is hitting the CCD this condensers are being charged. When the CCD is on, the current on this small condencers are increasing. The longer the exposure are (or stronger light) the higher current. When the processor want to read the CCD, it is discharging the cells (pixels) and collecting the current. This empties the CCD cells and the CCD is forced to make a new exposure(start all over).

adam8080 wrote in post #7639652
In film, you can't do that because each frame has a physical start and end, but that isn't the case with digital.

Well in a way it is the case, because the start point is when the CCD is allowed to start collecting light energy, the end point is when the CCD is discharged so the camera can read the information.

Ok then, what is the longest exposure possible for a 30fps video?

adam8080 wrote in post #7640607
Ok then, what is the longest exposure possible for a 30fps video?

The reading of the CCD is so fast so you can say that if the video is running at 30 fps the longest exposure would be 1/30. On a film camera you must have a shorter exposure, if the camera is running at 24 fps, you can not expose at 1/24 because the camera need to have time to move the film forward and get the new frame in to place, so max exposure would be perhaps less than 1/30.

Ok.

blue9 wrote in post #7642492
The reading of the CCD is so fast so you can say that if the video is running at 30 fps the longest exposure would be 1/30.

But my Sony FX1 can do right down to 1/4, with all of its glorious and crazy motion blur.

I'm too tired to comprehend all of the technical speak above at the moment, but that part I am sure of

adam8080 wrote in post #7639652
In film, you can't do that because each frame has a physical start and end, but that isn't the case with digital.

OK ... so a digital camera sensor (CCD or CMOS) works by converting light (photon) into electric charge (electrons), just like a solar cell ... but the sensor physically stores the electrons in the area that they were create (pixel area) so that image information is retained in the sensor.

The issue with "overlapping" exposures, is that the charge has to be physically moved OFF the sensor, to be read and converted to digital. By reading the sensor, the image is moved off ... so you can't keep "adding" to that image after it was read .. the sensor is empty once it's been read.

This usually works by simply doing a 1/4 second exposure, and writting it out to several frames. Capture the video into a computer and you'll see that, at 1/4 second shutter speed, blocks of as many as 8 frames together will probably have the same image.