30p or 24p?

Could just be my eyes Nick, but to me at least it isn't an attractive look when played back at 'normal' speed. Interestingly I'm very happy with shutter speeds up to 1/500 when shooting 60p for x2 slowmo. Work that one out!!

Could just be my eyes Nick, but to me at least it isn't an attractive look when played back at 'normal' speed. Interestingly I'm very happy with shutter speeds up to 1/500 when shooting 60p for x2 slowmo. Work that one out!!

24p was chose as the framerate for film because it's the lowest framerate at which our eyes and brains detect smooth motion. Your comment makes me wonder if there's an upper limit, too, at which we can't distinguish anymore; at that point, if there's enough frames there, the shutter speed might not make a difference because our brains aren't fast enough to process the number of images separately.

To try to answer the original poster's question, there are tradeoffs with each frame rate you choose. As others have said, if you are shooting for somebody else, then they will dictate the frame rate. If you are shooting for yourself, then you need to be aware of some limitations in the camera.

HD-SLR's have an upper limit on the amount of data they record per second (this is where you hear about AVCHD 2.0 28Mbps (28 million bits per second) and AVCHD 1.0 21Mbps). It is the camera's job to compress a 1920x1080x24 bit frame into a frame that can be recorded without exceeding 28 Mbps (which is just 3.5 MB/s). If you look at the raw data rate for 1080p30 (1920x1080 pixels * 24-bits color per pixel * 30 frames per second), we are talking about compressing 178 MB/s into just 3.5 MB/s, which is a little over 50:1 compression! Cameras have very sophisticated compression algorithms. The first thing they do is throw out most of the color information (which is why it is so important to white balance when recording video). After that, they do tricks like encoding only the parts of the picture that change from frame to frame. Keep in mind that in the end, the camera cannot exceed the data limit (28 Mbps, 21 Mbps, or 17 Mbps). If you have ever seen a sporting event on TV, when they show a bunch of fans jumping up and down and waving things in the air, the picture starts to break up into lots of blocks. This is what happens when the compression algorithm can't keep up with the amount of changing data from one frame to the next.

Ok, so why did I tell you all of that? The different frame rates you asked about all need to get compressed into one of the bit rates of the standard. Canon uses 44Mbps for both HD modes (1080p and 720p) on their HD DSLR cameras, so the compression rates are the following (by video mode):

1080p24: 26 to 1

1080p30: 32 to 1

720p60: 29 to 1

So, as you can see, the different video modes require different amounts of compression. If the scene you are recording has very little fine detail or motion, then you probably won't see any difference between the formats (as far as loss of detail due to compression), but if you are shooting something with a lot of detail and a lot of motion (say a bait ball), then the higher the compression, the more loss of detail. What you have to do is shoot some scenes in the three video modes and watch the playback to decide if the loss of detail is visible or not.

The advantage of 720p60 is that you can slow it down 2 to 1 for nice slow motion shots of that bait ball. Of course, you have much less resolution (1280x720 vs. 1920x1024), but from what I have read, there isn't really more than 720p actual resolution in a 1080p recording from Canon cameras. Again, you need to do some test shots to see what you think based on what you shoot and how you display it.

By the way, you cannot compare data rates across cameras because each has their own compression algorithm, and the quality of the compression is different. The current king of compression for consumer grade cameras is the Panasonic GH2 (when hacked). People have been recording at an astounding 190 Mbs, which for 1080p30 is a compression rate of just 7.5 to 1. Also, that camera has a very good compression algorithm, so it does a lot with those 190 Mbs. Of course, whether you need that high of a data rate depends on what you are shooting and what you want to do with the video you shoot.

Here are two nice reviews of the video capabilities of the Canon 60D and 7D that I found on the internet. They explain a lot of the differences between video modes:

http://www.imaging-resource.com/PRODS/E7D/E7DVIDEO.HTM

http://www.imaging-resource.com/PRODS/E60D/E60DVIDEO.HTM

I hope this helps.

--Mark

That surprises me. If all of the 60fps are being displayed during playback, I'd expect it to appear smooth even if there's an ultra-fast shutter and zero motion blur on each frame.

The higher the shutter speed in relationship to the frame interval, the bigger the gap there is between the end of one frame recording and the start of the next. If the subject you are filming is high speed, it will appear to jump between frames.

e.g if you are shooting at 25p, you are recording 25 frames per second, or one frame every 1/25th of a second.

If your shutter speed is open for 1/50th of second, the first half of the frame interval will record, the second half wont. If we go to 1/250th of a second, the first 1/10th of the frame interval will record, the last 9/10ths wont

If you're having trouble visualising how that would look, think of somebody running across stage with a strobe light flashing, first in an even/binary on off on off, then in an uneven on, off for long interval, on, off for long interval

1/2 on 1/2 off is sort of the de-juro standard (180 degree shutter angle), although opinions as always differ.

If you have a look at the following timelapse (topside, sorry!), initial shutter speed was set to 1/800th of second, ramping to 5 seconds exposure on a 7 second interval

Big Ben Timelapse - Shutter effect example

You can see massive shutter effect at the start of the sequence, the shots slowly smooth out as the shutter speed tends more towards 50% of the frame interval (i.e. shooting to 180 degree shutter angle)

I know about the trade-off between frame sharpness and motion blur, with 180 degree shutter angle being "standard". But Simon says this doesn't seem to apply to 60p shot at 1/125. I had even been thinking that one might be able to reduce the shutter angle to less than 180 degrees at these higher framerates (48p and higher) and still maintain smoothness. I think blaise may have a good point. Maybe our brains can't process all of 60 frames per second, so perhaps there is some shutter speed "ceiling" between 1/60 and 1/125, faster than which motion will cease to look smooth, no matter what the fps.

I know about the trade-off between frame sharpness and motion blur, with 180 degree shutter angle being "standard". But Simon says this doesn't seem to apply to 60p shot at 1/125. I had even been thinking that one might be able to reduce the shutter angle to less than 180 degrees at these higher framerates (48p and higher) and still maintain smoothness. I think blaise may have a good point. Maybe our brains can't process all of 60 frames per second, so perhaps there is some shutter speed "ceiling" between 1/60 and 1/125, faster than which motion will cease to look smooth, no matter what the fps.

Sorry Nickk, just read the whole thread... hope the egg I tried to show you how to suck didn't get too stuck in your throat!!

Based on the fact that we are able to see "analogue video" (i.e real life) without issues, my simple mind tells me that high frame rates should be OK too.. the more you have, the more they tend towards infinity, or "analogue". Perhaps the "gaps" tends toward infinity as well and so we see more of them, or perhaps, as you suggest, there's a shutter speed ceiling after which our eyes can't discern the blur, a circle of confusion/DoF allowance type thingy for smoothness?

Personally I haven't noticed it, but then it's not something I've used much. I'm perfectly happy with 25p playback,i t looks smooth enough to me, and gives me the most latitude on shutter speed/expsoure, so I'd only use higher frame rates if I wanted slow mo.

On that point, I got my hands on a Sony NEX-700 on Monday for a play, ran off some simple high speed tests as 200, 400 and 800 fps. I'll throw up my thoughts and video links to the results if anyone is interested.

I has a chat with a colleague/friend about this this morning, point he made which may be relevant is that the image/shutter open event isn't binary,i.e it probably takes a while for the sensor to power up and start receiving light/recording an exposure, possibly more so on a rolling shutter. It would be interesting to see if the same effect was apparent it as apparent inn a global shutter sensor.

Here are some of my observations on 60p playing back at 60fps:

Shooting panning shots, 60p with 1/1000sec shutter will still appear noticeably smoother than 30p with 1/60sec shutter. Maybe my eyes are not as sharp, I can't tell apart 60p with 1/60sec and 1/125sec shutter. Yes, some cameras can shoot 60p with 1/60sec shutter for low-light situation.

However, if the subjects move fast enough to cover distances far apart from frame to frame like balls traveling at high rate of speeds, then I'll be able to see a little strobing at 60fps if the shutter is set well above 1/125sec.

As always, different situations require different settings!

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Buyer beware! Not all cameras with 60p or 60i specs can deliver REAL 60fps! For example: None of the MFT cameras released in 2011 and 2012 "so far" (6/30/2012) can deliver "real" 1080 60i or 720 60p since their sensors only output 30p.

It could be solely down to personal taste but if I get a chance over the next couple of days I'll shoot 60p at various shutter speeds and we can play it back at normal speeds and look over the examples. I can't guarantee I'll have any willing subjects for repeatable tests but I'll do my best!....

The record on/off snapped on my housing

I'd managed to shoot 1/500 and 1/250 which look more or less the same. Oh well still traveling but will post examples when I get home if I think there is a point without the slower shutter speeds.

Oops, which housing Simon? I hope you can get it fixed.

If you can't do underwater tests, some topside tests would be nearly as useful. Just video of someone walking perhaps?

Hugyfot. Sometimes I love that housing and at other times aarrrggggghhhhh! It's due for some maintenance but even so you don't expect the external controls to start snapping (the camera on/off has cracked now too).

I recorded some topside examples and admittedly they didn't look as bad as they had in the past but that was using an IS lens. I'll try it handheld on a non IS lens and see what that looks like and post the results when I get home.

Cheers, Simon