Canon HG10-PF24@12FPS, how is it possible? at DVinfo.net

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Old October 22nd, 2007, 12:38 AM   #1
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Canon HG10-PF24@12FPS, how is it possible?

Hi all,

I've been perusing the .PDF manual for the HG10 while I wait for my camcorder to arrive, and noticed on p.45 it lists the operating mode and shutter speed info, with the following:

CAMERA Video - Shutter Speed as low as 1/30
CAMERA Video with PF24 frame rate - as low as 1/12
CAMERA Photo - as low as 1/15

I really got this camcorder intending to exclusively shoot 24P, and I'm guessing the 1/12 shutter speed explains why the cameras low-light capabilities are best in PF24 mode (vs. 1/30 in "standard" 1080i mode), *but* what I can't understand is:

How can you shoot 24 frames per second with a 1/12 s shutter speed? Doesn't this mean that when the frame is "done" the exposure is only "half-done?" Are they doing some trickery by frame doubling to effectively yield 12 frames per second in low light, or perhaps some other form of trickery? Does anyone know?

Thanks,

mike@slavis.com
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Old October 22nd, 2007, 12:59 AM   #2
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It just is 12 frames per second instead of 24. Instead of recording one frame per frame in 24p, you record 2 of the same frame in 24p. So it'll appear stroby like a lower frame rate should but with far more motion blur.

And there is a fact that 70% of the population cannot sense frame rate, but that's off-topic.
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I wait for the day cost-efficient global shutter 60fps capable CMOS sensors emerge for use on major manufacturers' cameras. (Sony, Canon, etc.) Rolling Shutters are a plague.
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Old October 22nd, 2007, 04:03 AM   #3
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The manual is actually wrong, it will allow all the way down to 1/6 second exposure.
I like these slow shutter speeds being available, they allow me to capture events in very dark surroundings in full color ( vs night shot modes ).
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Old October 22nd, 2007, 09:54 AM   #4
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Jack, thanks for the confirmation, that was my suspicion. On your "off-topic" comment about frame rate sensing, I would think that the "detection" of frame rate by the human eye/mind would vary by individual but at some point it will be detectable by everyone. For example, imagine watching a video at 2 FPS? I think everyone would see the jerkiness in that. I'm sure the movie studios did "extensive" studies before they settled on 24 FPS for movies. Back in the day, each frame of film cost money to purchase and develop, so I'm sure they were looking to optimize this cost and still achieve a satisfactory result.

Les, I'll check for the 1/6 on my camcorder when it arrives as well. Does this mean the camera is actually doing 6 FPS when this is chosen (Frames quadrupled in the 24 FPS stream within the 60i stream)? Man that could make your head spin...I'm guessing Canon did this for the reason you name, being able to capture events in dark lighting with full color. The sacrifice is motion blur and frame smoothness. However, most of these shots are probably not of the "high action" type, so the tradeoff is most likely valid. Also, on most of the low light tests done by reviewers they probably wouldn't even notice the 1/12 or 1/6 effective frame rate as they're usually shooting static targets. I'm also guessing this kind of trickery is only valid for progressive frames, or they would have followed suit on the interlaced side of the cam (where the slowest shutter is 1/30 s, which is the result when two interlaced fields are combined). Of course, for low light, the f/1.8 aperture maximum is nice as well.

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Old October 22nd, 2007, 10:19 AM   #5
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hmmmmmm....

Interestingly, on p. 54 of the User Guide, it lists different values for the slowest shutter. I'm guessing based on this that the values on p. 45 apply when the cam is in P mode, and the values on p. 54 apply when the can is in Tv mode (shutter priority). According to p. 54, in Tv mode, you can go down as far as 1/8 for 60i and 1/6 for PF24 (confirming what Les had found). So, I guess my speculation about the low light capability acheived by frame doubling/quadrupling was incorrect, and it can apply to interlaced video as well, in Tv mode.

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