24f vs 24p

[Nate Weaver]

Originally Posted by Zulkifli Yusof

The mechanics of a film camera 25fps (PAL) is achieved with the shutter going at 1/25th sec which I'm sure alot of people already knows. But for video cameras, DV or HDV, why is it that some sources recommend shooting at 1/50th sec to achieve 25fps?

You're confusing frame rate with shutter speed.

You're right, the shutter "goes off" every 1/25th of a second in a film camera (in Europe), but the same film camera will NOT have a shutter speed of 1/25th. Shutter speed is defined by how long the light strikes the film (or CCD).

So imagine in a film camera, 25 times a second a picture is taken. Each time, after each is taken, the film is advanced to the next frame. While this happens, the film has to be protected from light (shutter closed). The shutter in a motion picture camera is usually a spinning disc with a portion removed, typically 180 degrees worth.

So this means for half of the discs rotating travel the film is behind the solid part, actively being moved into position for the next frame. Then the film stops, the "open" part of the disc swings by for an exposure (180 degrees worth). As the shutter closes, the film advances again.

This means if the film is running at 25fps, it gets exposed for only 1/50th of a second (180 degrees of 25fps)

There are some film cameras that allow the shutter to be opened up to 200 degrees, as well as other cams that allow it to be closed down to 45 or 22 degrees (of which you can calculate the shutter speeds for at a given framerate). But the vast majority of film material shot is with a 180 degree shutter.

[Lawrence Bansbach]

Originally Posted by Jemore Santos

. . . why is the Sonys' V1 calling it 24p even though they're using interlaced CMOS?

They are? My understanding is that to do 24p, the V1 CMOS chips scan progressively and then the camera splits each progressive frame into two fields, intersperses 12 synthetic judder frames, then lays it all out to tape at 60i.

[Zulkifli Yusof]

Ah, yes. Thanks for clearing that up for me Nate. All along I keep thinking that framerate = speed of shutter, but now I know better.

[Nate Weaver]

Originally Posted by Lawrence Bansbach

They are? My understanding is that to do 24p, the V1 CMOS chips scan progressively and then the camera splits each progressive frame into two fields, intersperses 12 synthetic judder frames, then lays it all out to tape at 60i.

I've heard both. Regardless, it winds up with usable 24p however it does it.

[Timothy D. Allen]

Originally Posted by Nate Weaver

The Canons, the XCDAMs, and the V1 all look fine to me.

Nate,

What are you thoughts on what JVC is calling the first true "completely progressive" HD image for their HD100-HD250 series?

[Bill Pryor]

My thought: Marketing hype.
Maybe Canon should say, "First true 24F full HD resolution progressive."

[Thomas Smet]

It is not marketing hype.

What they are talking about is that they finally have the true 60p broadcast format for HDV and not just limited to 30p which looks good but isn't what true 720p 60p should look like. In order to be a true progressive 720p camera it has to be able to record 60p for HD broadcast work.

If you only ever plan on shooting 24p well then it doesn't really matter. At the same time however the HD100 does not fit the full specs of 720p so it cannot be a true 720p progressive camera.


When compared to DVCPROHD, remember that DVCPROHD 720 actually only reocrds with 960x720 anamorphic pixels. This means even the 720p TV shows shot with the Varicam are not really 1280x720 pixels of resolution at 60 fps.

The JVC HD200/250 is the first 720p camera on the planet that not only shoots full framerate 60p but also records to tape the full 1280x720 pixel raster. This really is a first for 720p HD and is actually the first 720p camera to totally fill and conform to the 1280x720px60p specs.

[Timothy D. Allen]

Sweet...

So if I'm understanding what you're saying – that you can capture 60 full frames per second – then this is the first HDV camera, of its caliber and price range, to provide full progressive in-camera slow motion as well!

By this I mean recording at 60p, and then dropping it into a 30p or 24p timeline.

Is this an accurate statement?

[Bill Edmunds]

So does 30f or 24f give you the same crystal clear still frames that 30p or 24p offer (as opposed to interlaced video)?

Is the pulldown-achieved 24p claimed by the Sony V1u really the same thing as Canon's 24f?

[Terence Murphy]

I'm curious about the benefits of 30f vs. 60i deinterlaced in post (besides the time benefit). Is there any difference between the two when shot with a 1/60sec shutter? That is, is the 30f image blended from two fields from the interlaced CCD, taken sequentially for 1/60sec each, just like the deinterlaced 60i?

And what happens with a faster shutter speed (other issues with faster shutter speeds aside), say 1/600sec (to keep the math simple)? In 30f, will it take one field at 1/600 and IMMEDIATELY take the second field at 1/600, make the frame, sit for 18/600, and then repeat the process? Or will it take one field at 1/600, sit for 9/600, take the second field at 1/600, sit for 9/600, just like 60i mode would? The first technique would exacerbate the stutter from the fast shutter but would maintain vertical resolution and make great stills. The later technique wouldn't offer any picture quality advantages over deinterlaced 60i (that I can see).

Of course, that's assuming your deinterlacing software is comparable to whatever voodoo Canon is doing on the camera. Has anyone made any comparisons of how well Canon's frame-mode deinterlacer compares to different deinterlacing programs you can run in post?

-Terence