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-   -   Questions HD-25p 50 or 25 frames per second? (https://www.dvinfo.net/forum/general-hd-720-1080-acquisition/140257-questions-hd-25p-50-25-frames-per-second.html)

Mark Smith December 24th, 2008 04:59 PM

Questions HD-25p 50 or 25 frames per second?
 
Apart from the difference in f stop, why would anybody want to shoot with a 25 shutter speed per second instead of 50 shutter speed per second?

50i = 50 interlaced frames, I therefore assume 50p is the same as 50i apart from there are 50 full frames instead of 50 alternate half field frames. Is this correct?

If so, what is the difference between the 50 full frames? is it a repeat of each of the 25 frames to make two identical frames and if so what would be the point of creating two identical frames?

I hope someone can understand me because I dont know the differences to be sure.

JVC GY-HD111e is my camera.

Tripp Woelfel December 24th, 2008 07:44 PM

50i isn't actually 50p. 50i can be de-interlaced to create 25p. You're fudging your nomenclature a bit. 50i is 50 fields per second. It takes two fields to make a frame, hence 25 frames per second. If you think in terms of fields per second you'll soon end up in a hedge.

If you're shooting 50i, you want to shoot at 1/50 or higher so that each field gets its own image. That will make the motion look smoother. You can shoot at 1/25 if you need to but you'll end up with the same image on both fields. Effectively the same as shooting 25p but not quite. As you said, you're repeating the same image for both the upper and lower fields. There's probably some reason why people don't do this to create ersatz 25p but I don't know what that is.

You cannot actually shoot 50p with the majority of tape cameras. There might be a few out there but I cannot list them since I live exclusively in the land of Canon.

Hope that helps.

Shaun Roemich December 25th, 2008 06:10 AM

Tripp: The JVC 2xx series will do 50P in 720.

Mark: Tripp is right in everything else in his post. 50P gives you 50 full progressive frames at 1280x720 in one second. 50i gives you 25 frames, each comprised of 1280x360 lines of odd scan lines, followed by 1280x360 lines of even scan lines.

I'm not sure if I can use slow shutter (meaning a shutter speed slower than the fps) on my HD200's. That would involve an accumulator buffer to "store" ambient light from previous frames/fields. I know my old Sony PD150 had it but it was DEFINITELY an effect and not for general use.

As you probably know, your 1xx series camera will only do 24/25P in HDV or 50i in DV. You don't have the 50P option in HDV until you go to the 2xx series.

Mark Smith December 25th, 2008 02:09 PM

My Camera Video Format Menu Screen
 
Quote:

Originally Posted by Shaun Roemich (Post 983686)
Tripp: The JVC 2xx series will do 50P in 720.

Mark: Tripp is right in everything else in his post. 50P gives you 50 full progressive frames at 1280x720 in one second. 50i gives you 25 frames, each comprised of 1280x360 lines of odd scan lines, followed by 1280x360 lines of even scan lines.

I'm not sure if I can use slow shutter (meaning a shutter speed slower than the fps) on my HD200's. That would involve an accumulator buffer to "store" ambient light from previous frames/fields. I know my old Sony PD150 had it but it was DEFINITELY an effect and not for general use.

As you probably know, your 1xx series camera will only do 24/25P in HDV or 50i in DV. You don't have the 50P option in HDV until you go to the 2xx series.

When you say my1xx series camera cant do 50p in HD, I would like to list for you what my camera option settings are since you never mentioned SD, it says in the menu I can do 50p but the 50p is 576 instead of 720 as follows below:

JVC GY-HD111e
Frame Rate Options
60/30 shoots at 480/60p or 720/30p
50/25 shoots at 576/50i, 576/50p, 576/25p or 720/25p
24 shoots at 720/24p

Record Menu Options
HDV-SD60p = HDV format shoots using a 480/60p signal
HDV-HD30p = HDV format shoots using a 720/30p signal
HDV-SD50p = HDV format shoots using a 576/50p signal
HDV-HD25p = HDV format shoots using a 720/25p signal
DV-50i = DV format shoots using a 576/50i signal
DV-25p = DV format shoots using a 576/25p signal
HDV-HD24p = HDV format shoots using a 720/24p signal

I presume that smoother footage can be obtained in HDV-SD50p with a shutter speed of 1/50th sec than if I used HDV-HD25p with the same shutter speed 1/50th sec

Would I be correct in what I say their and that the difference would be as follows, 50p is smoother than 25p both at the same 1/50th shutter speed even though they are different qualities HD & SD?

Simon Denny December 25th, 2008 05:22 PM

I think if you shoot with 720/50p, shutter needs to be 1/100 or double that of frame rate.

Shaun Roemich December 26th, 2008 08:25 PM

Quote:

Originally Posted by Simon Ash (Post 983867)
I think if you shoot with 720/50p, shutter needs to be 1/100 or double that of frame rate.

I shoot at a shutter of 1/60 at 720P60 here in NTSC land. No problems. I would assume that 1/50 at 50P would be just as acceptable.

I was unaware that the pseudo HDV SD mode would do 50P on the 1xx series cameras. I stand (somewhat) corrected.

Mark Smith December 27th, 2008 02:40 PM

50p capture
 
Thank you all for your comments.

I have Final Cut Express, I can capture 25p at its current settings, my question is:

Will I have to change the capture settings in order to capture 50p footage?


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