Flash Interference at DVinfo.net

Richard Peddington · February 3rd, 2009, 05:04 AM

Hello All,

I've been having an issue with my Z7U ever since I got it and can't seem to find any info on it. Thought it might have been the "rolling shutter" issue but it's not related. I shoot wedding videos, and whenever I'm filming at the same time a photographer takes a picture with their flash on, 3-5 frames after the flash become corrupted. My partner has uploaded an example of this to his Vimeo, which is located at Untitled on Vimeo. Just wondering if anyone has had this problem and so, has found a cause/solution. Thanks for reading!!

Rich

Gary Nattrass · February 3rd, 2009, 06:44 AM

Do you deliver your final videos interlaced? it looks like an interlacing problem to me.

Try exporting in progressive or de-interlace to see if it improves it. Also what shutter speed are you using?

Keith Forman · February 3rd, 2009, 09:14 AM

Quote:

Originally Posted by Gary Nattrass

Do you deliver your final videos interlaced? it looks like an interlacing problem to me.

Try exporting in progressive or de-interlace to see if it improves it. Also what shutter speed are you using?

I wouldn't do that. It will really change the look of the video and introduce artifacts. The interlace issue may be less present on a TV monitor rather than a computer. Make a test DVD and look at it on your TV.

keithdbf

Gary Nattrass · February 3rd, 2009, 09:36 AM

I export 1080i 25p so get the best of both worlds, try 1080i at 30p or 24p

Sorry for any confusion over interlacing.

Richard Peddington · February 3rd, 2009, 03:50 PM

Thanks guys for your input. It's actually really difficult to see in that video what I'm dealing with. I've compliled a page on our site that illustrates the issue a bit better - http://www.mgxproductions.com/flashissue. I'm not talking about the split flash (due to shutter speed), but it's the corruption of the entire image in between the 2 main flashes.

Gary, I've always liked to use a constant shutter speed of 60, so I can focus my attention on the exposure settings. However, I've tested it at different speeds, and auto, and it renders the same unwanted effect. Also, I've tested exporting at different frame rates and it's actually worse :(

If I downconvert to DVD the problem is greatly reduced, however I only have this problem with this camera which I use strictly for HDV projects (Blu-Ray).

I'm surprised nobody has noticed this before on this camera. Could it be a defective camera I wonder?

Keith Forman · February 3rd, 2009, 04:23 PM

Quote:

Originally Posted by Gary Nattrass

I export 1080i 25p so get the best of both worlds, try 1080i at 30p or 24p

Sorry for any confusion over interlacing.

Yes, that would work for future shooting...

Gary Nattrass · February 3rd, 2009, 04:41 PM

Could be a defective camera as you say, I standardise at 1080i 50i shooting at shutter speed 100. I then edit to master at 1080i 25p and have seen the rolling shutter effect but not pronounced lines like your problem. I have only seen that when there has been an interlacing problem.

Richard Peddington · February 4th, 2009, 05:03 PM

I tested it at home and the problem seemed to be resolved when I switch to progressive. But that doesn't help because I've always shot weddings in 29.97 interlaced. I wonder why it's doing that. Has ANYONE at all had this issue in the past? There has to be some way to resolve it and if not that's a huge issue. If nobody's had this problem, I'm going to have to assume it's a defective camera and have it repaired.

Thanks for reading :)

Stuart Nimmo · February 6th, 2009, 10:28 AM

I'm almost sure that it is the CMOS shutter Richard, I looked into the problem at great length before buying my HDV camera. This and the motion problem really concerned me as I do a lot of helicopter shooting.

Richard Peddington · February 7th, 2009, 07:21 PM

Stuart thanks for your input. What motion problem are you talking about? What camera did you end up getting?

Stuart Nimmo · February 9th, 2009, 09:41 AM

Well Richard, it's a delicate subject maybe. I don't intend to put people off at all, in any case the CCD - CMOS debate has been covered in detail.

Basically it's a matter of shutter types and what they will do for you. CMOS itself seems to have much to recommend it (better battery life, light sensitivity and the lack of flare off bright light for instance). However, it comes with a "rolling shutter" and I'm not so sure about it, certainly for the work I do. There are always technology trade-offs and there are rolling shutter issues in flash camera situations (almost inevitable at weddings I guess). As with a film shutter the flash speed can 'outwit' or conflict with the shutter speed and you may well get the sort of half exposed, "I can see the shutter" result demonstrated.

More importantly for me is the vertical distortion and very apparent image disturbance that can be introduced under certain shooting conditions. As I understood it, at the time there was no Post Prod fix for these phenomenon. It comes down to camera movement and there are one or two fairly devastating examples in the above article, I do recommend that you read it carefully and follow ALL the links in it as the possible effects are very clearly shown. I also suggest that the following "learned article" would be of interest to you, after all it's best to know about these things so that you can avoid the situation:

http://robotics.eecs.berkeley.edu/~s...metric2006.pdf

I have a good broadcast cameraman friend who's just got himself a Z7, so I'm showing an interest in what's being discussed here on this forum (I'm usually over at the JVC GY-HD strand). He feels that the Z7 is right for him. Personally I felt that a CCD camera with a global shutter was more likely to suit my needs and, (if I dare say it here) I got myself a JVC GY-HD 201E(b) which, although you wouldn't say it is light sensitive, I'm generally very pleased with it. As ever it's now been superseded but the Z7 will be soon, that you can count on. Sadly cameras seem more and more disposable these days.

I wish you all well with your choices!

February 3rd, 2009, 05:04 AM	#1
Richard Peddington Regular Crew Join Date: Jan 2009 Location: Canada Posts: 32	Flash Interference Hello All, I've been having an issue with my Z7U ever since I got it and can't seem to find any info on it. Thought it might have been the "rolling shutter" issue but it's not related. I shoot wedding videos, and whenever I'm filming at the same time a photographer takes a picture with their flash on, 3-5 frames after the flash become corrupted. My partner has uploaded an example of this to his Vimeo, which is located at Untitled on Vimeo. Just wondering if anyone has had this problem and so, has found a cause/solution. Thanks for reading!! Rich

February 3rd, 2009, 06:44 AM	#2
Gary Nattrass Trustee Join Date: Apr 2008 Location: Cornsay Durham UK Posts: 1,992	Do you deliver your final videos interlaced? it looks like an interlacing problem to me. Try exporting in progressive or de-interlace to see if it improves it. Also what shutter speed are you using? __________________ Over 15 minutes in Broadcast Film and TV production: http://www.imdb.com/name/nm1044352/

February 3rd, 2009, 09:36 AM	#4
Gary Nattrass Trustee Join Date: Apr 2008 Location: Cornsay Durham UK Posts: 1,992	I export 1080i 25p so get the best of both worlds, try 1080i at 30p or 24p Sorry for any confusion over interlacing. __________________ Over 15 minutes in Broadcast Film and TV production: http://www.imdb.com/name/nm1044352/

February 3rd, 2009, 04:41 PM	#7
Gary Nattrass Trustee Join Date: Apr 2008 Location: Cornsay Durham UK Posts: 1,992	Could be a defective camera as you say, I standardise at 1080i 50i shooting at shutter speed 100. I then edit to master at 1080i 25p and have seen the rolling shutter effect but not pronounced lines like your problem. I have only seen that when there has been an interlacing problem. __________________ Over 15 minutes in Broadcast Film and TV production: http://www.imdb.com/name/nm1044352/

February 9th, 2009, 09:41 AM	#11
Stuart Nimmo Regular Crew Join Date: Aug 2006 Location: Paris France Posts: 89	CCD Global shutter - CMOS Rolling shutter Well Richard, it's a delicate subject maybe. I don't intend to put people off at all, in any case the CCD - CMOS debate has been covered in detail. Basically it's a matter of shutter types and what they will do for you. CMOS itself seems to have much to recommend it (better battery life, light sensitivity and the lack of flare off bright light for instance). However, it comes with a "rolling shutter" and I'm not so sure about it, certainly for the work I do. There are always technology trade-offs and there are rolling shutter issues in flash camera situations (almost inevitable at weddings I guess). As with a film shutter the flash speed can 'outwit' or conflict with the shutter speed and you may well get the sort of half exposed, "I can see the shutter" result demonstrated. More importantly for me is the vertical distortion and very apparent image disturbance that can be introduced under certain shooting conditions. As I understood it, at the time there was no Post Prod fix for these phenomenon. It comes down to camera movement and there are one or two fairly devastating examples in the above article, I do recommend that you read it carefully and follow ALL the links in it as the possible effects are very clearly shown. I also suggest that the following "learned article" would be of interest to you, after all it's best to know about these things so that you can avoid the situation: http://robotics.eecs.berkeley.edu/~s...metric2006.pdf I have a good broadcast cameraman friend who's just got himself a Z7, so I'm showing an interest in what's being discussed here on this forum (I'm usually over at the JVC GY-HD strand). He feels that the Z7 is right for him. Personally I felt that a CCD camera with a global shutter was more likely to suit my needs and, (if I dare say it here) I got myself a JVC GY-HD 201E(b) which, although you wouldn't say it is light sensitive, I'm generally very pleased with it. As ever it's now been superseded but the Z7 will be soon, that you can count on. Sadly cameras seem more and more disposable these days. I wish you all well with your choices!

February 3rd, 2009, 03:50 PM	#5
Richard Peddington Regular Crew Join Date: Jan 2009 Location: Canada Posts: 32	Thanks guys for your input. It's actually really difficult to see in that video what I'm dealing with. I've compliled a page on our site that illustrates the issue a bit better - http://www.mgxproductions.com/flashissue. I'm not talking about the split flash (due to shutter speed), but it's the corruption of the entire image in between the 2 main flashes. Gary, I've always liked to use a constant shutter speed of 60, so I can focus my attention on the exposure settings. However, I've tested it at different speeds, and auto, and it renders the same unwanted effect. Also, I've tested exporting at different frame rates and it's actually worse :( If I downconvert to DVD the problem is greatly reduced, however I only have this problem with this camera which I use strictly for HDV projects (Blu-Ray). I'm surprised nobody has noticed this before on this camera. Could it be a defective camera I wonder?

February 4th, 2009, 05:03 PM	#8
Richard Peddington Regular Crew Join Date: Jan 2009 Location: Canada Posts: 32	I tested it at home and the problem seemed to be resolved when I switch to progressive. But that doesn't help because I've always shot weddings in 29.97 interlaced. I wonder why it's doing that. Has ANYONE at all had this issue in the past? There has to be some way to resolve it and if not that's a huge issue. If nobody's had this problem, I'm going to have to assume it's a defective camera and have it repaired. Thanks for reading :)

February 6th, 2009, 10:28 AM	#9
Stuart Nimmo Regular Crew Join Date: Aug 2006 Location: Paris France Posts: 89	I'm almost sure that it is the CMOS shutter Richard, I looked into the problem at great length before buying my HDV camera. This and the motion problem really concerned me as I do a lot of helicopter shooting.

February 7th, 2009, 07:21 PM	#10
Richard Peddington Regular Crew Join Date: Jan 2009 Location: Canada Posts: 32	Stuart thanks for your input. What motion problem are you talking about? What camera did you end up getting?