Frame split defect with strobe light

[Average Joe]

I'm new here, but I thought I'd chime in.

My friend Rick is the prop maker for the "Men In Black" films. One of the most difficult props for this production was the "Neuralyzer" (the memory eraser device they use throughout the films). If you remember the film, the Neuralzyer would "flash" when someone's memory was erased. The reason it was such a hassle was because of the flash duration. ILM did the final effects for the film, but the Neuralyzer had an actual strobe in the unit for reference. When they would fire it during a take, it was very hit or miss with the film cameras. In other words, the flash was too fast for the camera to capture all of the time. They solved the problem by eliminating the electronic flash from the unit and replacing it with one of those old polaroid camera flashes (the ones that fire once and then bubble up and burn out). The "duration" of the polaroid flashes was long enough for the camera to see.

I guess what I'm saying is, this happens with 35mm film cameras also. If the duration of the strobe is too fast it is hit or miss. Sounds like RED is behaving exactly like a regular film camera in this regard.

John

 

[jbeale]

I have simulated lighting strikes without synchronization using a very large photo flash (Norman P2000) set to have a very long duration (near 50 ms).

Impressive! Good to know, I wasn't aware that duration was available. All of my (much smaller) flashes have a shorter duration output; I think 1/1000 sec (1 ms) at most.

They solved the problem by eliminating the electronic flash from the unit and replacing it with one of those old polaroid camera flashes (the ones that fire once and then bubble up and burn out). The "duration" of the polaroid flashes was long enough for the camera to see.

I remember the little flash cubes on my 110 pocket instamatic about 30 years ago. They used magnesium-wool in a small plastic-coated glass tube. Are these still manufactured? I thought they'd been obsolete and off the market for about 20 years now. ...hmm, I see they are still on the market! http://www.flashbulbs.com/bulb_price.htm

 

[Brandon Fraley]

I guess what I'm saying is, this happens with 35mm film cameras also. If the duration of the strobe is too fast it is hit or miss. Sounds like RED is behaving exactly like a regular film camera in this regard.

John

it's one thing to simply miss the strobe and another when it repeatedly only shows half of it on the screen. I have faith that the RED team knows what their doing, but those frames are gross

 

[laguun]

cmos has other advantages.
instant readout is not one of them.

Thats one of the advantages of (frame) interline charged coupled devices (IT and FIT CCD), they can do that.

 

[kmikami]

To minimize this effect I propose to use 2k windowed (if the readout is faster) at 72fps, so that you could always get a usable frame fully flashed.

Wouldn't you still get the artifact if the strobe happened to shut off during the middle of one of the frames, no matter how quickly the readout happens? Maybe it's not the speed of the strobe that matters so much as the transition period between on and off, as suggested above by Average Joe. If a strobe changes nearly instantaneously from light to dark then the problem with always potentially exist with a cmos chip, right?

 

[Finner]

As Jarred indicated we will have true 360 degree shutter, it's not enabled yet

Won't this give you a strange very video look and tough to intercut with the standard shutter shots?

This seems like it will cause problems on shots as simple as man walks into room and turns on or turns off lights?

 

[Michael Ragen]

That is probably very true about the scenario Finner is talking about.

If I am understanding this correctly, If the man turns on the light in mid frame readout there would be one frame where only the lower half of the room would appear to be lit.

Once playback is enabled there should be an option to go frame by frame to make sure this effect does not appear in a key shot.

 

[Finner]

Directors are not going to scrap a take they like for this frame problem. It sounds like this flaw can not be fixed in the sensor so hopefully a quick post fix is introduced as commercials, Music vids, TV and feature work have different forms of flashes consistantly involved in shooting them.

 

[Jarred Land]

you guys crack me up.... turning on a normal lightbulb will not exhibit this effect.

 

[kmikami]

What if you turn it on really really fast?

 

[Joe Walker]

From my understanding this only happens when the flash goes off "down the barrel" of the lens, right? In other words, if you're filming some chick getting down in the club with strobes flashing, so long as they're not flashing down the lens, you'll be in the clear, right?

 

[Kevin Halverson]

From my understanding this only happens when the flash goes off "down the barrel" of the lens, right? In other words, if you're filming some chick getting down in the club with strobes flashing, so long is there not flashing down the lens, you'll be in the clear, right?

It has nothing at all to do with the admittance angle of the event. It has everything to do with the dynamic profile of the event. A strobe has a fast (short duration) dynamic profile, an incandescent (practical or otherwise) has a very slow dynamic profile.

Really, this isn't anything to be concerned about except for some very specific situations. The situations that would cause any effect at all are not unique to the RED, its just the nature of any shutter (electronic or mechanical).

 

[Finner]

you guys crack me up.... turning on a normal lightbulb will not exhibit this effect.

On set turning on a light switch does not mean a normal light bulb comes on. Usually there are 2 or even three tungsten lamps I will have the gaffer snap up on a variac when the set-deck light switch is turned on. So if this problem happens from a flash of light I would think it could happen then. Now the variac may very well slow the speed of the light to a slow enough flash speed that the frame split defect would not happen but that would need to be tested to know for sure.

Also what about flashing cop light, flashlights, lighthouses, sun glints off of polished cars and headlights... there are a multitude of other forms of flashes, or does the sensor not split those flashes? Maybe they are to slow.

Please understand I am just asking what will and what won't cause these split screen problems and not stateing that these will cause the defect.

 

[Kevin Halverson]

On set turning on a light switch does not mean a normal light bulb comes on. Usually there are 2 or even three tungsten lamps I will have the gaffer snap up on a variac when the set-deck light switch is turned on. So if this problem happens from a flash of light I would think it could happen then. Now the variac may very well slow the speed of the light to a slow enough flash speed that the frame split defect would not happen but that would need to be tested to know for sure.

Also what about flashing cop light, flashlights, lighthouses, sun glints off of polished cars and headlights... there are a multitude of other forms of flashes, or does the sensor not split those flashes? Maybe they are to slow.

Please understand I am just asking what will and what won't cause these split screen problems.

The larger the incandescent source (read power) the slower its profile. This is due to having finite source resistance in the mains (inclusive of all aspects of the mains path). Even the smallest practical is way too slow to exhibit any issues. Have you every watched a 10k come on or go off?

The examples you site are absurdly too slow to be of any concern at all. Again, this camera's characteristic isn't any different than any other camera with a shutter (read every camera in use on any film set anywhere).

 

[Finner]

Have you every watched a 10k come on or go off?

Yes I have, have you??? When I work with 10k lamps they are HMI's so if you have any experience at all with an HMI light you would understand that they have no bearing what so ever on this problem. If you would like an instructional tutorial about how HMI's work please PM me as I would be happy to help you learn a little.

The examples you site are absurdly too slow to be of any concern at all. Again, this camera's characteristic isn't any different than any other camera with a shutter (read every camera in use on any film set anywhere).

Is that so. What is absurd is someone that is going to make statements like you have without ever actually shooting any tests or projects with the camera they are claiming they know the characteristics of.

I have shot 5 commercials with 2 reds and this camera does have a shutter that reacts very different from every camera that I have shot with because of the way the sensor works.

Before you make statements like the ones above please have some experience and facts to back them up.

By the way I will help you get a better understanding of how fast flashing sun glints happen off of car headlights. I have shot car commercials where you will get a single frame of a headlight glint when overcranking at 150fps with an ARRI 435. If you need an easier laymans explanation of that please PM me and I will help you learn what all that means as well.

 

[Kevin Halverson]

Yes I have, have you??? When I work with 10k lamps they are HMI's so if you have any experience at all with an HMI light you would understand that they have no bearing what so ever on this problem. If you would like an instructional tutorial about how HMI's work please PM me as I would be happy to help you learn a little.

You may wish to reread my post, I clearly stated an incandescent source, which clearly an HMI is not. What I am trying to convey, is that you have to consider the dynamic profile of the illumination source. If its profile is slow, the effect will not be exhibited, if it is fast enough (and improperly timed in relationship to the shutter) then it might be an issue.

I am assuming that you meant to type 'HMIs' and not 'HMI's' (plural, not possesive).

 

[ChrisLyon]

or cite, not site.

sorry i had to say it. forgive me. 0:|

 

[Finner]

I am assuming that you meant to type 'HMIs' and not 'HMI's' (plural, not possesive).

I will not argue for a second that my grammar and spelling is not my forte. It does however seem to be yours so you may wish to take up writing over cinematography.

 

[ChrisLyon]

I'll step in beyond my blood-curdling comment about "cite" and "site" - I suck at spelling. But that is neither here nor there.

I think we are all getting a little tense lately. Myself included. I think this goes back to the whole "The RED is out and we aren't getting answers" plea. Or that we are getting answers that in turn generate more questions.

Let's all back off a bit and sing Kum Ba Yah or something. Let's applaud the people who own Reds and wait until they post more footage to begin ripping things apart again. No need to do it to each other in the meantime.

 

[Häakon]

"Cite" and "site" barely scratch the surface of egregious spelling and grammar errors all over REDUser. I get a migraine just loading up the front page. But I realize that no one seems to care about proper form anymore, so I have chosen to be nice and hold my tongue... except of course when I feel it necessary to poke a little fun at Jarred and his contstant misuse of your/you're. ;-)

But really, this all takes a back seat to the topic at hand... no light bulbs with RED!!! I can see the headlines on cinematography.com now...