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Old June 8th, 2005, 07:31 AM   #1
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Shutter speed

I've seen several posts regarding requirements to convert standard DV to 24p, and all indicate shutter for NTSC should be 1/60th....what if I decide I don't want to convert to 24p after shooting....how will this effect my footage, i.e., can I still edit and render without effecting the appearance of the footage.
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Old June 8th, 2005, 08:02 AM   #2
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1/60 is the default shutter speed for everything because it matches the way your camera (assuming your in the US using NTSC) captures images. With interlaced video, every other scan line is captured 60 times each second, and these are called "fields". Putting two fields together gives you a complete picture, so that takes 1/30 second. So when you set the shutter at 1/60 (which it should be unless you specifically change it) you get the maximum amount of data that your camera can deliver, and that's why the deinterlacing ("film look") software suggests that you use 1/60.

Now if you set the shutter to a high speed, like 1/500 sec for example, that means during each of those 1/60 intervals where a field is captured, you will only grab a quick 1/500 sec time slice. This might be useful for analyzing a golf swing for example, since you get a series of sharp images without the motion blur of a 1/60 sec exposure. But when played back in motion it will have a distinctive look that's sort of choppy. It's an effect that you may want to use sometimes, but probably not for everyday shooting. And it won't work well for software that deinterlaces the image or changes the frame rate. Do the math.... 1/60 = 0.167 and 1/500 = 0.002, so for every field there's 0.165 seconds where you don't have a record of what's happened.

OTOH, you can also shoot at shutter speeds slower than 1/60. This has its own issues however. If you shoot at 1/30 sec it means the shutter is staying open for two complete field captures. This results in something called "field doubling" which means that the same data is written to both fields. Remember, normally your camera captures the odd 240 lines of video in the first field, then the even 240 lines in the second field. Combined you get the full 480 lines in 1/30 second. But if you shoot at 1/30 sec exposure then only 240 lines are captured, and they are written to both the odd and even fields. The result is that you lose 50% of your vertical resolution.

There can be good reasons to use shutter speeds other than 1/60 second, but unless you have one it's usually safest just to stick with the default. Try some experiments at different speeds and see how you like them. This all assumes you're using full manual control on your camera. If you set the camera for auto, it may very well choose different shutter speeds all by itself to get what it thinks is proper exposure. You should avoid this since it can produce some inconsistent results.
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Old June 8th, 2005, 10:30 AM   #3
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Boyd...thanks for the clarification...
Regards - David Bird
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Old September 7th, 2005, 12:59 PM   #4
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shutter speed for 25p in PAL?

I was wondering if it has to be 1/25, which the XL2 defaults to. why wouldn't it be 1/50? if you set it to 1/50, the warning light comes on in the VF. I can't see a huge difference in the end product.
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Old September 7th, 2005, 01:05 PM   #5
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Hmm, that's odd. I'd think it would default to 1/50 since the format is generally called "50i", much the same as 60i defaults to 1/60 shutter speed.

But you're using an XL2 which is progressive scan. So my guess is that you may be shooting 25 fps progressive, and that would certainly be preferable to shooting 50i and converting to 25p with software. Sorry, no experience with this camera... perhaps you should post your question in our XL2 forum here:

http://www.dvinfo.net/conf/forumdisplay.php?f=73
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Old September 7th, 2005, 01:15 PM   #6
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Boy, it's been awhile since I was on this thread...at any rate, I have a Pana AGDVC200 and the slowest shutter speed on the lens I have is 1/100th...what's that going to do to the footage I capture and convert to 24p
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Old September 7th, 2005, 01:28 PM   #7
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You need to read the documentation for the software you're using. DVfilm suggests 1/60 for NTSC or 1/50 for PAL. I suspect that 1/100 will create sort of a choppy effect. For every 1/50 of a second you're only capturing a 1/100 second slice. If this creates a problem then it would probably be most noticeable on fast movement.
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Old October 18th, 2005, 10:33 AM   #8
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Ok, I was shooting out doors with my XL2 and I noticed that I was not seing any footage on ehte VF until I increased the SP to about 4,000.

So how does this affect the default 1/60?
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