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Canon GL Series DV Camcorders
Canon GL2, GL1 and PAL versions XM2, XM1.


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Old May 28th, 2007, 02:09 AM   #1
Tourist
 
Join Date: Jan 2007
Location: anchorage,ak
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frames and shutter speed

hey everybody,

not sure if this question belongs here, but I use a GL2 (and love it!) so i'll just start at this forum.

My question is: exactly how do shutter speed and frame rate relate?
I understand shutter speed as far as still photography goes, but when i use FRAME MODE (30ish frames a second) on my GL2 with a shutter speed of 1/120, for example, does that mean that the camera records 4 distinct images per frame?

many say that i should shoot at 1/60 for the best filmic look but in bright settings that is way too much light even with the ND filter.

anyway, I guess practice makes perfect.

GL2 rocks.

thanks for any help,
Lee

ps any of you guys in the anchorage area? I am having a VERY hard time finding dedicated startup filmmakers.

Last edited by Lee Borghi; May 28th, 2007 at 02:11 AM. Reason: a p.s.
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Old May 28th, 2007, 06:16 AM   #2
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When you import your finished video, do you get that number of "distinct" frames coming?

I bet you don't.

So there is something else going on.

I video at 25fps - that's PAL. I can shoot with a shutter speed of 1/50 of a second. I can shoot with a shutter speed of 1/100 and that is 1/100 of a second. What this means is that the shutter is ONLY open for 1/100 of a second - but I still only have 25 frames.

When the Shutter speed is INCREASED from 1/50 to 1/100 it reduces the amount of light coming into the camera - it goes darker, the shutter is operating more often than before for ONE second.

But the frame rate - for PAL - is still 25fps.

On the other side, if the shutter speed is DECREASED it is open for longer - allowing MORE light into the camera - moving from 1/50 > 1/25 > 1/12 > 1/6 the MORE light I have coming in

But the frame rate - for PAL - is still 25fps.

I KNOW, this also took me some time to get a handle on it, and it was the "use" of the word "shutter".

A shutter used in stills means that which allows the film to be exposed to the light. But my understanding, here, has meant the the gate-shutter - the speed fps - at which the film passes the gate. I think this is where I picked-up my own confusion.

In any event, I don't have a means to alter that mechanical fps. Some dv cameras do. If I shoot in frame mode it still comes in at 25fps! I'll let somebody else explain Canon's Frame here!!

Now, and as you say, shooting for 1/60, PLUS the internal ND is still to bright. And from this I'm also assuming you don't want to move to faster shutter speeds. However, this doesn't affect the fps. You are still at - NTSC? - 60fps. BUT, if you WANT to stay at 60fps AND you want to be appropriately exposed for the shot, guess what you need to do? Either INCREASE the F stop number ( close down the Iris), which you may not want to do either OR slap even MORE ND on the front! And that's exactly I do. THEN you will have 60fps AT the F stop you want BUT have the appropriate exposure.

I really hope this has assisted you .. if anybody sees some holes in what I'm saying, please correct me - I MEAN IT!!

Oh, and onto the drive for FRAME mode that very "slight" invitation you made to discuss it. I think?

SD - HD - LCDs and CRTs
Is HD more or less like film? Discuss!! And where does OUR FRAME mode fit in anyway??

HD is very clear and sharp, but is it more or less like film? And yes, this IS an unfair comparison - but a comparison that takes WHAT we comprehend and visualize to yet another plane. What we know now is another way to see moving images. As it was at the turn of the last century with hand cranked cameras. HD is just a "further" development.

At the end of the day, it is ALL about the narrative, and how we engage with that narrative. Youngsters will soon ARE discarding the analogue qualities of the CRT in favour of the LCD flatties. Shame. But what they are seeing is very sharp, highly contrasting images.

Apologies for the digression . . lost me focus for a bit there . .

Grazie
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Old May 28th, 2007, 07:16 AM   #3
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Shutter speed is the duration of the exposure used to form the image. For most current camcorders it is the amount of time the CCD is allowed to gather light before it is read

Frame rate is how often the full image is updated in the video data stream, 29.97 times per second for NTSC. The NTSC frame has 525 lines, about 480 lines of visible video (the additional 45 lines are used for VITC, blanking while the TV tube trace moves to the top of the screen, etc.)

Interlaced (as in NTSC) means the frame is comprised of two fields, one with the even numbered lines and the other with the odd numbered lines, and normally each field is captured as a separate ("half image") 59.94 times per second. Thus for interlaced NTSC the slowest shutter speed for normal looking video would be 1/60.

Using a slower shutter speed (not all camcorders support this) will mean the fields will be updated less often than the standard rate, so you see image artifacts such as more motion blur and less smooth motion, and repeated identical fields.
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Old May 28th, 2007, 07:48 AM   #4
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Thanks Don! - A far simpler and better explanation than my hamfisted attempt. Thanks! - G
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Old May 29th, 2007, 10:34 AM   #5
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Quote:
...each field is captured as a separate ("half image") 59.94 times per second.
That is to say, a new field is capture 59.94 times per second, alternating between an even- and an odd-numbered line field.
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