[excuse-me]

Higher frame rate doesn't automatically translate as "better"

Our eyes (actually brain) have a natural fusion frequency, images shot with a relatively long exposure at 24fps - with corresponding motion blur - is different from shorter exposures at 48fps.

Remember Ray Harryhausen's stop motion monsters? Those are much 'sharper' than actors, but not necessarily more realistic ( except in the case of Keanu Reeves)

[jcampbell1]

The exposure length could be the same. 360 degrees of shutter at 48fps is the same exposure as the cinematic standard of 180degrees/24fps.

[excuse-me]

IIRC the Red camera has a rolling shutter so is equivalent to a fixed 360deg shutter

(if I understand cinema shutter terminology correctly ?)

[stephen_g]

The two things you posted are completely un-related.

Film cameras generally have a 180 degree shutter, which means that the film is exposed for half the time each frame is in the gate - which means at 24 frames per second, the exposure time is 1/48th of a second. A 360 degree shutter would theoretically therefore be 1/24th of a second at 24 frames per second, or 1/48th of a second at 48fps (so should exhibit similar motion blur to 24fps at 180 degree shutter).

The EPIC is perfectly capable of taking any of these exposure times (up to 360 degrees - I'm not sure what the limit is exactly at the low end - probably something like 1/10000th of a second).

Now, 'rolling shutter' is just the fact that each column of pixels along the sensor are read sequentially, so there is a slight difference in time from the first column to the last one being read (called the read-reset time). This can be really bad on cheap cameras with slow read-reset times, where it can cause vertical things like light-posts to look skewed when you pan across them quickly, but the EPIC's read-reset time is fast enough that it's not a problem (it is similar to the time it takes a film's mechanical shutter to blank).

[excuse-me]

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.

[jcampbell1]

The red camera has no shutter. It just reads from the sensor. It can set the exposure length to anything less than the frame rate minus the time to read the sensor. So at 48fps, the exposure can be 1/48 second minus the time to read the sensor, which is approximately equal to 1/48th of a second.

A film camera cannot do this because there must be time to move the film around, and so the standard design creates 24 frames per second, with 1/48th of a second to physically move the film, and 1/48th of a second to expose the film. Of course you could expose the film for less than 1/48th of a second, but that would create the problem you originally mentioned.

My point is that the RED camera at 48fps with the "shutter" always open, you have the same exposure length (and motion blur) as a standard film camera.

[excuse-me]

it has a shutter - it's simply electronic. The exposure is the time between the pixel reset and the readout. On the EPIC chip there is a full frame reset and a per row reset. On some scientific chips it's possible to reset an individual pixel immediately before reading it, it's even possible to read a pixel multiple times without resetting it so you can get multiple exposure times in the same pixel in the same frame!