Shooting 25fps in USA advice?

[Ron Evans]

Originally Posted by Gary Huff

You can shoot 60p with 1/60 shutter, just as you can shoot 24p with 1/24 shutter speed. Doesn't mean that's what you should be doing.

60i is 60 fields a second, each field is separated by a time delay of 1/60 of a second. Miniscule, but still there. These fields are combined to be 29.97 in frame rate, hence 1/60.

No they are not separated by any appreciable delay they come one after the other 59.94 of them a sec. 29.97 odd and 29.97 even scan lines. This is the cause of all the confusion. But this is why the temporal motion is the same as 60P. The number of exposures is the same. The fields are combined by whatever is receiving them. For a CRT they get displayed as they come in all 59.97 of them and no progressive frame is constructed at all. That is how the whole system was created. Hence one sees an apparent smooth 60fps image ( it flickers at a rate that is more than we can see so looks like a progressive image ) There are no jaggies on a CRT only on a display that has to create a progressive image. (You can see the lines if you go up close though. ) In that case there is a set of scan lines missing ( ether odd or even) that a flat panel TV for instance has to create. Good flat panel TV's do a good job ,not so good, well they have jaggies as does a computer monitor. The simple way of combining the fields and playing them twice leads to the worse image. Better TV's interpolate the missing field for each progressive frame created. To do this they need a storage memory to store several fields so that the missing fields can be interpolated. The higher the refresh rate and memory the more frames can be created or quality of deinterlacing improved. They also need an audio delay because of course this takes time.

NLE's usually allow the deinterlacing type to be selected. At least the ones I use do.

With a modern camera you can shoot with any shutter speed available. You may not like the result though.

Ron Evans

[Gary Huff]

Originally Posted by Ron Evans

No they are not separated by any appreciable delay they come one after the other 59.94 of them a sec. 29.97 odd and 29.97 even scan lines.

There is an appreciable delay. If there was not, you wouldn't get interlacing and tearing.

But this is why the temporal motion is the same as 60P.

This is true about temporal motion.

For a CRT they get displayed as they come in all 59.97 of them and no progressive frame is constructed at all.

All 59.97 fields are combined together, which is 29.97 frames per second. They are not "progressive" but they are combined.

The motion is the same, but the frame is made up of two separate fields that are 1/60th of a second apart in time and combined into a single frame.

With a modern camera you can shoot with any shutter speed available. You may not like the result though.

Exactly. Which is why you should shoot for your deliverable frame rate and set your shutter speed to the Hz level of the lighting in the country you are in to eliminate, regardless. As a side example, shooting at 96fps on the GH4 can lead to flicker because the shutter speed with a 180 degree shutter is 1/192. This doesn't divide by 60, and so you get flicker. I have to change my shutter speed to compensate for that. Same idea.

EDIT: So I was wrong about the shutter speed when it's set to an angle. Both the GH4 and the C100 Mark II set the shutter to 1/120 when it's set to 60i, which makes sense up further reflection since it is capturing 60 half frames a second.

[Ron Evans]

Yes this is very confusing. It was much better in my mind why 60i was just called 60i.

Also the reference you quote is wrong too. Don't believe everything you read on the internet. If the fields are 1/60 apart and there are 59.94 of them in a sec then the exposure rate is the same as 60P ( 59.94 fps ). The timecode for 60i is 29.97fps they are not picture frames. The frame sync was necessary for sync issues with CRT TV's and other equipment in the chain telling them this is a start of another sequence etc. The pictures are fields, timecode/sync is frames and the camera has to expose properly for each of these fields. You cannot equate interlace video and its timecode to film frames or to progressive frame rates. Fields were intended to get displayed in sequence on a CRT. A flat panel TV/monitor has to display a progressive image at 60hz or faster in North America. It cannot display a field so has to combine the fields to get a progressive image. Just adding them together is wrong and results in all the know artifacts. Simple de interlacing just added them together and displayed them twice resulting in the worse image possible !!! Destroying a smooth motion into a terrible 30P image displayed at 60P. As I mentioned in a previous post, modern TV's interpolate the missing scan line for each full frame and emulate the smooth picture of a CRT. To do this it needs several frames ( 2 fields ) to get enough data. Hence the audio delay. With these faster refresh rate these TV's can also correctly display 24P images by emulating a projector with multiple blade shutters or of course destroy the 24p cadence and substitute a high frame rate that I know annoys the purists.

Glad you got it sorted. It is very confusing.

Ron Evans