You still have an adjustable exposure time between the pixel reset and read, which you can make pretty small (<1ms)
But the real problem comes from the time taken to read an entire frame. On a cheap camera this is about the frame time because the electronics is slow, but on a high end camera it is still often close to the frame time because you have a lot of pixels and there is a limit to how fast you can read while still having low noise. Some scientific CMOS cameras get round this by having massively parallel outputs.
The problem gets worse at 48fps - if it takes close to 1/48s to read the chip then a moving object will have stretched across the entire frame from top to bottom. In the worst case a vertical post in a fast pan will be at 45deg. A 24fps camera run at the same pixel clock only has half the effect.
The cameras do have software to try and correct this - basically they look for vertical edges and de-skew them, but this puts in artifacts that you don't want in a Hollywood movie. The other secret is to not fast pan at 48fps.
Comments
You still have an adjustable exposure time between the pixel reset and read, which you can make pretty small (<1ms)
But the real problem comes from the time taken to read an entire frame. On a cheap camera this is about the frame time because the electronics is slow, but on a high end camera it is still often close to the frame time because you have a lot of pixels and there is a limit to how fast you can read while still having low noise. Some scientific CMOS cameras get round this by having massively parallel outputs.
The problem gets worse at 48fps - if it takes close to 1/48s to read the chip then a moving object will have stretched across the entire frame from top to bottom. In the worst case a vertical post in a fast pan will be at 45deg. A 24fps camera run at the same pixel clock only has half the effect.
The cameras do have software to try and correct this - basically they look for vertical edges and de-skew them, but this puts in artifacts that you don't want in a Hollywood movie. The other secret is to not fast pan at 48fps.