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CMOS chips- rolling shutter causing any ill effects for wedding videographers

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Olly Lawer
CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 20, 2009 at 9:32:28 pm

I have been doing quite a bit of reading on the difference between the CCD chips and CMOS chips. Apparently, although the CMOS chips can cause some rather bad artifacts, see here http://freshdv.dreamhosters.com/mjeppsen/video/ex1_strobe_cmos_rolling_shut... this effect can be greatly reduced if the electronic shutter is turned off - well at least with the EX1, i'm not sure about the Z7E.

I wonder, has anyone had any first hand experience of this with either camera?

Also, what is the difference between the SxS card set up on the EX1 compared to the CompactFlash that the Z7E uses. I'm pretty sold on the EX1, but am happy to be convinced otherwise. At this rate, I think i'd be better off getting a Z1 with CCD chips - damn site cheaper too - although as all the review sites keep telling me, the image quality of the EX1 is far superior to the Z1 and better for low light shots too.


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Craig Seeman
Re: CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 20, 2009 at 10:34:24 pm

[Olly Lawer] "although the CMOS chips can cause some rather bad artifacts"

While I haven't shot weddings with the EX, I do shoot a fair amount of press/speaking events and there's plenty of flashes going off. Basically the flash has to fill a significant portion of the frame to see it. I've shot fireworks on several occasions (and that's all flashes) and NEVER see it under that circumstance. Depending on where the flash occurs relative to where the frame is being scanned you get a partial frame flash.

Whether it bothers you (or your client) is an aesthetic thing. Different than CCD, Yes, bad, that's subjective. In all the stuff I've shot where I can that partial frame flashes not a single client or other viewer mentioned it.

I hope the following doesn't confuse you but JVC is moving to XDCAM EX codec and their cameras are CCD. The HM100 will only have 1/4" chips and the HM700 1/3" in what seems to be the 100/200/250 shoulder mount form factor. While it seems to support all the frame rates the EX series does the specs don't mention overcrank. So you'll have the choice between 1/2" CMOS from Sony or 1/3" CCD from JVC with your EX codec. I prefer the addition depth of field control on the EX as well as overcrank. Clients notice those features more than anyone ever noticing the partial frame flash.

[Olly Lawer] "Also, what is the difference between the SxS card set up on the EX1 compared to the CompactFlash that the Z7E uses."

I'm not sure what you're asking here. They're recording card formats. SxS is much more expensive than compact flash but you can use SDHC now with the EX too. The Z7 is HDV which forever knocks it off any camera list for me. I do NOT like the codec. Now if there's artifacts that'll bother you THAT is a codec I'd avoid. You can break the codec on fast motion and that bugs me far more than the occasional partial flash of the CMOS chip.



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Michael Palmer
Re: CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 20, 2009 at 11:56:06 pm

I think I'm now willing to part with my Z1 if you are interested. I have a few accessories I could use the money for and it just sits on a shelf. You can find my email on my profile if you are iterested in a good used Z1U.

Michael Palmer


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Rafael Amador
Re: CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 22, 2009 at 2:54:05 pm

There are people that thing this is not a solution, but so far i've been able to get rid of all the flashes in a couple of concert by shooting interlaced.
After you only need to apply a de-interlacer filter in just the frames with the flashes. In some frames you need to keep the upper-fields, in others the Lower depending in which field the flash happens. After, no trace of the flash.
Curiously I haven't came across with a picture with a flash in both fields. but even in this case could be done duplicating the frame.
Of course if you are shooting few hundred of flashes a day you better look for other solution.
rafael

http://www.nagavideo.com


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Olly Lawer
Re: CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 22, 2009 at 6:57:41 pm

Can I just clarify on what you mean when you say "there are people that thing this is not a solution, but so far i've been able to get rid of all the flashes in a couple of concert by shooting interlaced"?

The EX1 will mainly be used to film weddings, where there may indeed be lots of flashes; however, if by turning the electric shutter off and shooting in interlaced, this solves the problem, then great.

Does filming interlaced give similar results to progressive? I know the shutter speed doesn't stop any unwanted artifacts, but does shooting in other modes change it? i.e. 1080i compared to 720p?

Thanks



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Don Greening
Re: CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 22, 2009 at 8:04:32 pm

[Olly Lawer] "The EX1 will mainly be used to film weddings, where there may indeed be lots of flashes; however, if by turning the electric shutter off and shooting in interlaced, this solves the problem, then great."

You're worrying too much about this. It's not a huge issue. With a CCD camera a camera flash will blow out one entire frame of video and you can't see anything in that frame. With a CMOS camera only part of the frame will have the flash in it and a good portion of the time you'll still be able to see what's in that frame. So now you tell me which is more disruptive and obvious. Sometimes a recorded CMOS camera flash will be spread over 2 frames but sometimes not. It all depends on the timing of the flash in conjunction with the scanning of the CMOS chip because it's scanned from the top down whereas a CCD is scanned all at once.

[Olly Lawer] "Does filming interlaced give similar results to progressive?"

Yes.

[Olly Lawer] "I know the shutter speed doesn't stop any unwanted artifacts, but does shooting in other modes change it? i.e. 1080i compared to 720p?"

No, because it's got nothing to do with recording format or frame size. It's got everything to do with the way the CMOS sensor is scanned. I've recorded flashes in both interlaced and progressive and it always looks the same.

- Don



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Chris Babbitt
Re: CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 23, 2009 at 5:30:44 pm

I completely agree with Don on this. To me, the flashes are just as annoying whether they are full-frame or partial-frame. It's the flash that's the problem, not the rolling shutter issue.



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Rafael Amador
Re: CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 23, 2009 at 5:02:14 pm

[Olly Lawer] "Does filming interlaced give similar results to progressive?"
For many things even better. For example if you have to do any slow-mow you will get a much better from a i60 than from a p30.
I agree with Don that you bother too much about the flashes.
You should rent one day an EX-1 and make few tests.
rafael



http://www.nagavideo.com


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Craig Seeman
Re: CMOS chips- rolling shutter causing any ill effects for wedding videographers
on Jan 23, 2009 at 5:56:48 pm

[Rafael Amador] "For example if you have to do any slow-mow you will get a much better from a i60 than from a p30. "

Just to add explanation, having 60 images a second keeps greater temporal motion when slowing down in post production.

Of course shooting 24, 25, 30/50, 60p will be even better since there's no frame blending or optical flow calculation issues.

Of course one may find p60 (as 720p60) even better than i60 as you have 60 full frames to slow rather than interlaced fields.

[Rafael Amador] " agree with Don that you bother too much about the flashes. "
I'll "third" that. That's why I emphasize it's "different" not worse that CCD. It seems my clients don't complain at all about it. Don't forget CMOS has advantages over CCD as CMOS doesn't get that "smear" when hit with bright light. Of course the low power consumption of CMOS allows 1/2" chips to work in such a small form factor without overheating. My clients DO notice the shallower depth of field I can have and DO NOT complain about the how the flashes look. That tells the whole story for me as to the "business" of which camera to purchase.




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