Theories on casues for image flicker

[Matt Pacini]

I hope this is a Film Group modification problem, and not a universal problem.

You would think that they would know this, and have an indicator that shows at what point the batteries are low enough to cause this problem.

Matt Pacini

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[Scottness]

Yeah there is actually an indicator - it's the main light that's on when the unit runs - it jsut goes dim or flickers - our problem was we put the unit in a little bag to hang off the tripod and after one of the early shoots the cameraman forgot to unplug the lead and the battery drained in the intervening time (we were only shooting on the weekends) -- once we realsied that we always unplugged it and checked the battery all the time - but it's still a less than perfect situation you really need a meter or some more finite way of judging the battery level than how dim or flickery a light looks - lesson learnt -- by the way what do you mean by strobing MrObvious (great name by the way too!)

Scotness

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[Matt Pacini]

Since they know that if the battery is low, that sync is screwing up, I would think the smart thing would be for the unit to actually completely STOP the camera, if the power dipped below that point, so there would be no guessing.
Obviously, noobody would actually WANT what the unit is doing at that time, so that would make sense to me.
Maybe you guys should send your suggestions to Film Group for that.

Matt Pacini

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[Nigel]

I would think that could be solved by using a NiCad or MimH battery.

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[Scottness]

ANother possibility which I just thought of is the handle of the camera kept coming loose and we had to take the base plate off a number of times to tighten the screw inside which secures it to the body of the camera - with this a bit loose the body could have been shaking - even if the lense was a bit loose too I spose it could have shaken as well (I don't recall it being loose though) -- any thoughts on these ideas?

Scot M

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[Alex]

I'm curious about the maintenance history of your 4008.

Once the lubrication in the camera "dries" up,
the camera can have numerous "sticking" points that would lead to flickering.

I would also experiment with an external battery supply that just has a lot more juice.

I recently switched to 27amp hour batteries for video shoots where the cameras are tripod based and I won't be moving around.

One pleasantly surprising result was that over the course of a 90 minute shoot, the two cameras stayed in PERFECT time-code sync to each other....normally, I get a very minor drift over that length of time....

I am assuming the higher amp battery supply helped keep the time-code sync perfect between the cameras.

However, lubrication is still the key for the 4008.

Perhaps Nigel can volunteer who overhauls his 4008 and how often he has it done.

Film Group has some kind of warning about only doing the mod if the camera is in proper working order...I think we can all see why...(assuming your camera needs lubrication)

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Alex



[This message has been edited by Alex (edited September 24, 2001).]

[Nigel]

I have Irv Higdon in California overhaul my 4008. I have it done every 2 years. His number is 1-800-318-3259 or www.irvhigdon.com Good Luck

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[Matt Pacini]

[QUOTE]Originally posted by Nigel:
[B]I would think that could be solved by using a NiCad or MimH battery.


Yeah, but regardless of how long you can get useable power, if they know that, below a certain level of power, the unit is going to malfunction, then shouldn't they have an auto shutoff function?
Even the lowly Super 8 cameras, will not slow down when power gets low, they run at speed, or they stop.

Film Group has to know, that nobody is going to actually WANT to keep shooting, even though the unit is screwing up from not enough power.
Hey, Nigel, by the way, I am waiting on pictures of my film developer to get back, then I'll email them to you, & you can decide if you're interested. I'll give you first shot before I put it on Ebay.

Matt Pacini



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[Scottness]

Hi ALex - I had the camera serviced by the licensed Beaulieu service agent in Australia before I go the crystal synch add on. I haven't emailed The Film Group yet for their thoughts on all this - but will soon. The references to battery life in the posts above I thought were for the crystal synch unit, no tthe camera - I did get an external battery fitted to the camera whicl lasts for a squillion hours - we never flattened and I did recharge it a few times (which was probably not that smart considering I could have induced a memory effect in it - but I think at times we would have shot up to 40 cartridges with it before I recharged it - which I did just to be on the safe side, in case it ran out during the next days shoot). Does any of this fit the pieces together a bit better? In my mind it's most likely going to be something to do with the handle coming loose, or an internal mechanism in the camera - not the synch unit -- because it did it on about our 3rd roll when the synch unit would have been fine; but then alto of times it was worse at the start of a roll and then would settle down as the roll went and the synch unit changes and adjusts the speed of the camera each time you start - but there's a clue then - it'd do it at the start of each take on the roll, not jsut the start of each roll -- I guess it's a mechanical thing - I'm going to get the guy to look at it again.
Scot M

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[MovieStuff]

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by Alex:

I recently switched to 27amp hour batteries for video shoots where the cameras are tripod based and I won't be moving around. One pleasantly surprising result was that over the course of a 90 minute shoot, the two cameras stayed in PERFECT time-code sync to each other....normally, I get a very minor drift over that length of time....I am assuming the higher amp battery supply helped keep the time-code sync perfect between the cameras.<HR></BLOCKQUOTE>

Hmmmmm....

Unlike an analog audio recorder who's speed can be affected by voltage drain, video recorders use a crystal oscillator for reference when generating the control track pulses that determine playback speed on video. In fact, time code is not necessary at all to maintain perfect synch between two video decks, even over an hour or more.

Here's why:

Two decks will be laying down X number of control track pulses for X number of frames across an hour and that X number of frames will be the same on both decks because the oscillators in each deck are running perfectly in synch, just like watches and just like crystal controlled movie cameras.

The number of frames the two oscillators create will be the same regardless of the actual speed of the tape passing by. This is necessary because the engineers realized that as tape rollers and the such wear, the mechanical speed of the tape could slip and change over the life of the machine. When a tape from a worn machine is played on another machine, a synch circuit compares the pulses coming from the oscillator to the control track pulses (not the time code) on the tape. The motor then receives instructions to speed up and slow down to keep the tape pulses in synch with the oscillator pulses, even if the tape from the other machine was recorded a little "slow" or a little "fast". The originating speed makes no difference since the number of control track pulses from start to finish will be the same.

Therefore, when recording on two video decks, the synch is established by the oscillators BEFORE the time code cards generate a number and lay it down on each frame. That is why you can take two video decks without time code, line them up on the same frame and they will take off and play in synch. Even if they start off a frame or two different from each other, they will maintain that difference down to the end.

Now, what timecode DOES do on playback is allow for an even start so that decks are guaranteed to start on the same frame when released. However, once released, the decks can either chaselock to the control track pulses of house synch, the source deck or their own internal oscillators. In all of the above scenarios, time code is not required for maintaining synch between the decks.

More importantly, if you were shooting in the field with two video cameras and forgot to turn on your timecode generators or if they failed, you could tail slate the shot before turning off your camcorders then backtime the two tapes from that end clap. I guarantee you they will stay in synch without timecode just like shots from crystal synched movie cameras stay in synch without timecode. This is because time code has no critical bearing on synch between two players and even less between two recorders. The recorders will laydown identical frames at identical times whether the timecode generators are turned on or off; either the frames get numbered (for convenience in editing) or they don't, but the rate and number of frames generated stays the same.

So, actually, battery level should not affect time code accuracy or synch performance at all on video, so I suspect something else might be going on with your equipment. The reason is that decks should have an automatic cut off that prevents them from operating when they reach an undervolt status. You might check out that aspect of your equipment. However, any gross variations in power that was enough to throw off the timecode would cause noticable glitches in the recorded signal, I would think. But, I have seen stranger things happen in video. It's the devil's medium, after all.

Roger