Shooting 25fps in USA advice?
 

I'll be shooting indoor interviews in the USA for 25fps delivery with the EA50U. I'll be dual recording with the SDHC card plus Atomos Ninja Blade. My plan is to shut off the room lights and light it with only my Lowel Tungsten lights. I've switched my EA50 to 50i mode 1080 25P.
Any advice or things to look out for so I don't mess this up?

Re: Shooting 25fps in USA advice?
 

Set your shutter to 1/60th of a second

Re: Shooting 25fps in USA advice?
 

Hi David

Firstly 50i mode doesn't have 1/60th it's 1/50th but if you are in the USA and delivering to clients in the USA why are you switching to 50i?? Have they specifically asked for a end file in 25P??? Most, if not all NLE's can render out to any mode you choose so you could actually shoot in 1080 60P and then render out to 1080 25P without any problems.

Chris

Re: Shooting 25fps in USA advice?
 

Well, 60 is not divisible by 25. You could probably get away with it for talking heads as there'll be little motion, but since most cameras can easily support it, why not? If David knows it needs to be PAL rates, then he should shoot PAL and compensate for the Hz difference with the shutter speed.

Re: Shooting 25fps in USA advice?
 

Chris, Dave and Gary: Thank you very much.

I thought about shooting in 60P and outputting 25P since I realized talking heads would probably be ok, but I may not be the one editing the footage. The end user isn't in the USA and they want 25P so I need to shoot it that way.
I did some testing with my EA50 today and when I reboot to PAL 50i mode it does default to shutter speeds of 1/25 and 1/50 as expected but also lets me do 1/60 so I think it will be fine.
My main concern was electrical frequency problems in the lights conflicting with the PAL mode but it makes sense that the shutter is the key.

Re: Shooting 25fps in USA advice?
 

Hi David

I think I might gravitate towards 60i simply because of the light frequency ... even your lights will be running at 60hz so you might get some flicker. Why not do a mock setup with the lights at home and then shoot about a minute of footage first at 50 then at 60 and render both to 25P ??? Whatever looks best is what you need to use. To be honest I try to stay away from double frame rates if I can so for me 50P is seldom an option unless a client insists on it! You would be safer with either 1080 50i or 60i and then drop the interlaced footage onto a 25P timeline .. I do all my weddings like that despite what others say "you don't shoot progressive?" LED lighting kills footage done at 50P but I can get away with it easily at 50i

I don't know what NLE you use but with Sony Vegas if you render 30P to 25P it drops 5 frames each second ..... I wonder how 24FPS would work??? It's 24 FPS in either mode???

Chris

Re: Shooting 25fps in USA advice?
 

I don't think you quite grasp the concept of compensating for the light hertz. You do that with shutter speed, not with frame rate. At 60i your shutter speed (if we are talking 180 degrees) will be 1/60. Which is the Hz rating of lights here in the States. If you shoot 60p your shutter speed will be 1/120. There is no reason you cannot shoot 25p with a 1/60 shutter. Just don't use 180 degrees to shoot 25p because then your shutter speed will be 1/50.

Despite what others say? Who says this? You should always shoot progressive. Full stop. Again, you need to learn that frame rate and interlaced vs progressive has nothing to do with flicker. It's about the shutter. The only reason it would have an impact would be if you don't take your camera out of a 180 degree shutter.

If you shoot interlaced and have to deliver progressive, you toss away half your resolution. If you're shooting 2:2 pulldown in 50i, then you're not actually shooting interlaced in a way that would make any difference.

At 50p with a 180 degree shutter, your shutter speed is 1/100. At 50i, your shutter speed is 1/50. Do you see the difference?

Re: Shooting 25fps in USA advice?
 

50P and 50i just like 60P and 60i are taking the same number of exposures the only difference is that the interlace video is only recording half the vertical resolution. So the shutter speed will be the same for both. The temporal motion is identical. Also unlike a film camera where there is a physical spinning shutter a CMOS camera has no limit. It is up to the electronics to take the sample at what ever speed the camera can manage including the full time of exposure since there is no need to cover while the film advances. The reason for the spinning shutter. Shutter speed will effect the aesthetic of the video by inducing or controlling motion blur in conjunction with frame rate. For film makers transitioning to electronic cameras using shutter angle is sometimes included but in actual fact the camera is only controlling the sample rate from the sensor hence the term shutter speed or the speed of sample capture. How long does the camera allow the sensor to collect light before readout. Because of this there is almost infinite control over the shutter speed allowing for syncro scan for controlling flicker etc. There is no physical shutter for shooting video. Yes there are some video cameras with a physical shutter for taking stills too.



Ron Evans

Re: Shooting 25fps in USA advice?
 

You can easily test this. Set your camera to 180 degree shutter speed, then toggle between 60i and 60p and see the exposure difference.

Re: Shooting 25fps in USA advice?
 

For all my cameras that can shoot 60i and 60P there is no difference at all in exposure. In automatic exposure they all display the exact same values for iris, gain and shutter speed whether set to progressive or interlaced. If I set the shutter speed then the iris and gain are still the same. Shutter speed set is the shutter speed period. None of my cameras has a shutter angle setting only shutter speed. They all respond the same way whether in 60i or 60p with no difference in picture. Cameras that work this way that I have are Sony FDR-AX1, FDR-AX100, NX30U, CX700. The difference to the camera for interlace or progressive is what gets recorded or output. I expect that internally they are always in progressive mode likely true for most cameras that can do both interlaced and progressive. What gets recorded or output will depend on the internal electronics. The interlaced picture has half the vertical resolution of a progressive frame for each field and most modern TV's will interpolate the image to fill in the missing scan lines and process a progressive image for display anyway. But the camera exposure rate is the same for 60i as 60p , don't get confused by the 60i timecode of 29.97 fps. That is why 60i is smooth compared to 30P as it has the same exposure rate as 60P ( 59.94fps )

Ron Evans

Re: Shooting 25fps in USA advice?
 

I believe I made it pretty clear I was talking about shutter angle. If your camera does not have a shutter angle function, and you are using automatic settings, then you don't understand what it is I am talking about.

The rule of thumb is that your shutter angle should be twice your frame rate. 60p is 59.97 fps. 60i is 29.97 fps.

Re: Shooting 25fps in USA advice?
 

I understand completely what you are talking about. I think you may not understand that 60i timecode is 29.97 but the number of exposures are 59.94 exactly the same as 60P ( 59.94 ) So your argument of shutter angle has to be applied to the exposure rate not timecode a common misunderstanding. By the way I only mentioned automatic to show how the camera setting changed for progressive and interlace. They didn't because the shutter angle is the same for the exposure, same rate. Shutter angle is a film camera paradigm, Modern sensor camera do not have a shutter wheel rotating with blanking to allow the film to progress to the next registration.

If you don't understand the difference between 60i timecode of 29.97fps and progressive 30P ( 29.97P ) Take some video at both rates with some fast moving subject and compare. At the same time take some 60P and notice how the 60i and 60P played back on a modern interpolating LCD are virtually identical depending on how good your TV is at de interlacing. On my Sony 240hz TV I cannot tell the difference between 60i and 60P smooth motion for instance. There is a big difference in motion artifacts going to 30P or 24P.

Ron Evans

Re: Shooting 25fps in USA advice?
 

No it's not. The exposure for the second half of the fields comes after the first half, which is why the resolution is cut in half when you convert to progressive. It is a trick to get the motion of 60p without the actual bandwidth required. That's why you get tearing and interlacing in the image, because the two fields are not scanned simultaneously, they are scanned one right after the other. It's pretty fast, but definitely not simultaneous. Otherwise you're telling me all those old broadcast cameras were actually polling the sensor at a full 60p rate, which is nonsense.

Re: Shooting 25fps in USA advice?
 

No the old broadcast cameras were scanning fields one after the other as you describe which results in the same rate of exposure as 60P ( 59.97 fields a second ) when viewed on a CRT TV. Yes you and I understand why they did this then. However the timecode was calculated on frames , 2 fields make a frame hence 29.97fps hence the incredible confusion. But the number of exposures of the camera as you mentioned, one field after the other, is 59.97 as you described exactly the same as for 60P. So when setting camera exposure it would be the same as a film camera running at 60 ( 59.94) and the same as 60P. Exposure has to be set each time an exposure is made whether that is for a field or a frame. They are the same rate for interlace or progressive. The old cameras couldn't do progressive so the exposures were for each field. Modern cameras that can do both likely run in progressive all the time and only encode for recording or output. Some can record two variants and output a third. Again the exposure time is dependent on exposure rate and your guide would work fine. However with electronic controls rather than a spinning wheel there is a lot more control over the exposure time and better described as shutter speed.

Since this was started by someone with an EA50 I do not think the EA50 has a shutter angle control either it is the same as my Sony's using shutter speed as the control parameter. I know that using shutter angle on a film camera meant that changing frame rate would result in an automatic exposure rate change whereas using shutter speed one has to reset to the appropriate value for each frame rate. Something you have to do on most video cameras anyway.

Shutter angle is not new to me as I shot film in the early 1960's

Ron Evans

Re: Shooting 25fps in USA advice?
 

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.

Re: Shooting 25fps in USA advice?
 

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

Re: Shooting 25fps in USA advice?
 

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

This is true about temporal motion.

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.

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.

Re: Shooting 25fps in USA advice?
 

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