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Help with my sick Mitchell


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#1 walg

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Posted 10 April 2007 - 11:45 AM

Hello All,

I have a problem with my Mitchell Fries 35R which is used for motion control.

The problem is a flickering / double imaging mainly at the top of frame and mainly in areas of high contrast. eg black and white text.

I have shot various tests at various speeds and ruled out the pelicule.

The problem manifests itself worst at higher frame rates. Several people have looked at it for me. Like them I am at a loss.

The shutter is timed correctly and doesn't seem to be loose in any way. I was told when I started using the camera that the shutter had long since been 'fixed' at 180 degrees. I think they must have meant 170 degrees however since that is its maximum.

The pilot pins (registration pins) do however seem to be picking at the film at the beginning and end of the shutter cycle.

I ripped a small sample of video of the problem. The sample was shot at 100FPS and is zoomed in TK to about 200% at the top of frame. I uploaded the 1mb file to a file sharing site.

http://www.mediafire.com/?9nnnmqe3fwf

Any suggestions would be gratefully recieved.

John Wenman
Motion Control Camera Assistant.
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#2 Stephen Williams

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Posted 10 April 2007 - 01:54 PM

Hello All,

I have a problem with my Mitchell Fries 35R which is used for motion control.

The problem is a flickering / double imaging mainly at the top of frame and mainly in areas of high contrast. eg black and white text.

I have shot various tests at various speeds and ruled out the pelicule.

The problem manifests itself worst at higher frame rates. Several people have looked at it for me. Like them I am at a loss.

The shutter is timed correctly and doesn't seem to be loose in any way. I was told when I started using the camera that the shutter had long since been 'fixed' at 180 degrees. I think they must have meant 170 degrees however since that is its maximum.

The pilot pins (registration pins) do however seem to be picking at the film at the beginning and end of the shutter cycle.

I ripped a small sample of video of the problem. The sample was shot at 100FPS and is zoomed in TK to about 200% at the top of frame. I uploaded the 1mb file to a file sharing site.

http://www.mediafire.com/?9nnnmqe3fwf

Any suggestions would be gratefully recieved.

John Wenman
Motion Control Camera Assistant.


Hi John,

That's camera 297 or 298 then? I remember that problem from 1986.

What is happening is the register pins are still moving as the shutter is opening (or closing)! As I understand this is only happening at higher speeds, due to vibration. It's a case of motor tuning. However it's quite likely that due to wear in that 80 year old camera that you won't fix it.

What you could do is make the shutter fixed at about 144 degrees & retime the movement with the extra safety margin both sides. I did that once with a Mitchell used for animation.

FWIW I wanted to dry hire your rig about 6 months ago, your producer was not interested however.

Stephen
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#3 walg

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Posted 11 April 2007 - 10:13 AM

Hello Stephen,

Forums never cease to amaze me! A camera that old with an unknown problem and we get an informed answer within hours from a man who actually knows the camera. It is indeed camera number 297.

Our Mitchell is sadly now in pieces with the movement, flywheel and gate on its way to Fries Engineering so sadly I can't perform any more tests. I have passed on this information to our engineers who in turn have passed it on to Fries.

We were pretty sure the problem lay with the pins but I confess we didn't look into the motor or its tuning. Several people with far more camera knowledge than myself have told me that our movement is very 'sloppy' and in real need of a decent service and if necessary some new parts. Hopefully then its journey across the pond will not be entirely wasted. Our Mitchell is still a very busy camera. We maybe shoot 10-20 rolls of film a week with it and regularly put it through its paces at 100 FPS so it's hardly surprising when it needs a bit of attention.

In the meantime we are having a universal camera platfrom made which will allow us to use an ARRI camera and also to offer various HiDef solutions. Until this is ready we will be shooting on dodgy Beta.

As for our producer not being interested in a dry hire. I'm sorry to hear that. I was never asked whether dry hire was a possibility.

If you are ever in Wardour Street please feel welcome to pop in and say hello. We are ' Rushes Studio' nowdays and have moved the rig downstairs to a slightly larger room. Mark Roberts have done an excellent job over the years keeping the rig in tip top condition and I like to think that Central Londons only motion control studio is here for a good many more years.

Thanks for the reply and I will let you know how we get on when we get the camera up and running again.

John Wenman

Motion Control Assistant.
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#4 Stephen Williams

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Posted 11 April 2007 - 01:49 PM

Hello Stephen,

Forums never cease to amaze me! A camera that old with an unknown problem and we get an informed answer within hours from a man who actually knows the camera. It is indeed camera number 297.

Our Mitchell is sadly now in pieces with the movement, flywheel and gate on its way to Fries Engineering so sadly I can't perform any more tests. I have passed on this information to our engineers who in turn have passed it on to Fries.

We were pretty sure the problem lay with the pins but I confess we didn't look into the motor or its tuning. Several people with far more camera knowledge than myself have told me that our movement is very 'sloppy' and in real need of a decent service and if necessary some new parts. Hopefully then its journey across the pond will not be entirely wasted. Our Mitchell is still a very busy camera. We maybe shoot 10-20 rolls of film a week with it and regularly put it through its paces at 100 FPS so it's hardly surprising when it needs a bit of attention.

In the meantime we are having a universal camera platfrom made which will allow us to use an ARRI camera and also to offer various HiDef solutions. Until this is ready we will be shooting on dodgy Beta.

As for our producer not being interested in a dry hire. I'm sorry to hear that. I was never asked whether dry hire was a possibility.

If you are ever in Wardour Street please feel welcome to pop in and say hello. We are ' Rushes Studio' nowdays and have moved the rig downstairs to a slightly larger room. Mark Roberts have done an excellent job over the years keeping the rig in tip top condition and I like to think that Central Londons only motion control studio is here for a good many more years.

Thanks for the reply and I will let you know how we get on when we get the camera up and running again.

John Wenman

Motion Control Assistant.


Hi John,

I know that camera from about 1987. It had the same problem & flickered like hell at 25 fps. At the time it had an IMC stepper drive that vibrated. A Fries motor was purchased and flicker at lower speeds was then acceptable. When MRMC upgraded the rig about 10 years ago they locked off the planatary gears so the shutter was then fixed at 170 degrees.

I was using an identical AF 35 R yesterday on a IMC rig (sn 749). In the past I have spent a couple of days eliminating flicker on that camera by motor tuning. I guess Peter from MRMC will have to check your camera on it's return. I am surprised that it still has a flywheel, MRMC normally remove them, it helps with animation but may cause problems like you are experiancing when there is wear in the movement.

I assume you oil the camear every day and every take at 100 fps, it needs it!

I have seen that problem come & go at higher speeds, it might be fine at 99 fps but at 100 it's there. Reducing the shutter slightly will work if the worst comes to the worst.

If you need any further help, my mobile phone no is on my website.

Stephen
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#5 Phil Rhodes

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Posted 11 April 2007 - 05:18 PM

Hello John

I think we worked together on some strange oven chip thing just before christmas.

Phil
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#6 Stephen Williams

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Posted 12 April 2007 - 10:03 AM

Hi John,

Whilst you are dealing with Fries, I would recommend you change the first roller before the main sprocket to a larger plastic one. This puts less stress on the film at high speed, I am also convinced that there is less dirt on the neg too after the upgrade! Cost was $175 last time I bought one.

Stephen
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#7 walg

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Posted 12 April 2007 - 10:07 AM

Hi Phil,

Sadly / happily it was not me you worked with. I was feet up on an island in South Easy Asia.

I saw the ad though. It looked great.

John










Hello John

I think we worked together on some strange oven chip thing just before christmas.

Phil


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#8 walg

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Posted 13 April 2007 - 08:20 AM

Hi Stephen,

Thanks. I know exactly what you mean. I have passed this forum link on to our engineers and in turn hopefully Fries. When the camera gets back we will look into the tuning. I have checked our settings and to be honest they seem a little on the high side.

I converted to Flair NT fairly recently. I wonder if the settings got changed accidentally in some way while importing the old settings. When I get some time next week I will boot up the old Flair and check.

I will keep you posted as to how we get on.

Thanks again

John
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#9 Stephen Williams

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Posted 13 April 2007 - 09:16 AM

Hi Stephen,

Thanks. I know exactly what you mean. I have passed this forum link on to our engineers and in turn hopefully Fries. When the camera gets back we will look into the tuning. I have checked our settings and to be honest they seem a little on the high side.

I converted to Flair NT fairly recently. I wonder if the settings got changed accidentally in some way while importing the old settings. When I get some time next week I will boot up the old Flair and check.

I will keep you posted as to how we get on.

Thanks again

John


Hi John,

The best motor tuning I had with #749 was 3,8,8! Gave far better results than the MRMC settings. I bought a flicker tester from them so was able to play!

Stephen
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rebotnix Technologies

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Visual Products

Rig Wheels Passport

Media Blackout - Custom Cables and AKS

Abel Cine

Tai Audio

Wooden Camera

The Slider

Ritter Battery

Aerial Filmworks

Gamma Ray Digital Inc

Glidecam

Opal