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#1 Paul Bruening

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Posted 31 December 2009 - 11:09 PM

Hey fellas,

The FFD on the 35R3/Nikon F-mount is supposed to be 46.5mm or 1.8307in. It reads out to 1.827in. or 46.4058mm. How much variance is tolerable? Should it be dead-on? Should it actually go a little deeper to expose for the middle layer of film? We're only talking about 3.7/1,000 of an inch.

Who sells individual sheets of the plastic shim stock that I'll need?
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#2 Stephen Williams

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Posted 01 January 2010 - 02:08 AM

Hey fellas,

The FFD on the 35R3/Nikon F-mount is supposed to be 46.5mm or 1.8307in. It reads out to 1.827in. or 46.4058mm. How much variance is tolerable? Should it be dead-on? Should it actually go a little deeper to expose for the middle layer of film? We're only talking about 3.7/1,000 of an inch.

Who sells individual sheets of the plastic shim stock that I'll need?



Hi Paul,

PL has a nominal 52mm however I would depth measure the camera between 51.97 - 51.98mm. Hope that helps.

Stephen
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#3 John Sprung

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Posted 01 January 2010 - 04:00 AM

An error of 0.0037" is way too much. +/- 0.0005" is more like it.




-- J.S.
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#4 Tim Carroll

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Posted 01 January 2010 - 08:37 AM

Hey fellas,

The FFD on the 35R3/Nikon F-mount is supposed to be 46.5mm or 1.8307in. It reads out to 1.827in. or 46.4058mm. How much variance is tolerable? Should it be dead-on? Should it actually go a little deeper to expose for the middle layer of film? We're only talking about 3.7/1,000 of an inch.

Who sells individual sheets of the plastic shim stock that I'll need?


Paul,

We shoot for plus or minus five thousandths of a millimeter. So yeah, 3.7 thousandths of a inch is pretty much "way off".

Alot of us camera techs get our plastic shim stock from a place called Artus Corporation in Englewood NJ and their phone number used to be (201)568-1000. You probably want the Shim Stock 5" x 20" packet, which is the colored plastic stock. Comes in thicknesses from .0005 in. to .030 in. in 15 steps. You can probably find them on the web.

Best,
-Tim
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#5 Paul Bruening

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Posted 01 January 2010 - 03:11 PM

Thanks, fellas,

I can't even count all of the times ya'll have helped me out with information.

I just emailed Artus for a price quote on the plastic shim stock pack. Should I just pick the single sheet that best fits or should I stack them to get the precise shimming?
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#6 Tim Carroll

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Posted 01 January 2010 - 06:06 PM

Thanks, fellas,

I can't even count all of the times ya'll have helped me out with information.

I just emailed Artus for a price quote on the plastic shim stock pack. Should I just pick the single sheet that best fits or should I stack them to get the precise shimming?


Would recommend getting the whole pack. Chances are, you might need to experiment with a few different sizes or size combinations to get it right.

Also, how are you measuring the FFD? We use really precise gauges (that read down to .001 mm or at least .01 mm) and "standards" that are precisely 52mm (for ARRI cameras). What are you using for your measurements?

Best,
-Tim
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#7 Paul Bruening

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Posted 01 January 2010 - 09:03 PM

Would recommend getting the whole pack. Chances are, you might need to experiment with a few different sizes or size combinations to get it right.

Also, how are you measuring the FFD? We use really precise gauges (that read down to .001 mm or at least .01 mm) and "standards" that are precisely 52mm (for ARRI cameras). What are you using for your measurements?

Best,
-Tim

I'm using a piece of string and my left pinky fingernail.

I've got a depth micrometer that measures in .000". I have to get online to do the conversions back and forth to metric. I went to a machine shop supply store in Tupelo and got a set of parallels that were already the proper dimension in thickness and film frame height. I used my Dremel cut-off wheel to cut it to the remaining dimension (the metal was so hard that a hack saw just skated around without cutting). I took great care not to bung-up the surface. These parallels are rated to .003" tolerance. I drop it in, replacing the pressure plate, and roll the spring clip onto it. Then I wedge a bit of popsickle stick into the clip to make sure the parallel doesn't rise off the gate during measurement.

I've got a lot more of this parallel material left over if one of you could use a chunk. I don't know about other cameras, but it dropped into place on my Mitchell perfectly.
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#8 Chris Millar

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Posted 01 January 2010 - 10:16 PM

I'm using a piece of string and my left pinky fingernail.

ahh, but how long is that piece of string ?

After 12 months the human eyeball stops growing and settles at an average 24mm diameter - 24x2 = 48mm - close enough (:blink:)

I'd just eyeball it - snort snort :lol:
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#9 Hal Smith

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Posted 01 January 2010 - 11:07 PM

Tim's +/- .005mm is equal to +/- .0002". That's a pretty tight tolerance, the type of tolerance that only people like tool and die workers and camera technicians work with on a regular basis. In my sportscar racing days I used to deal with ten-thousandths occasionally in engine work (piston pin fit for instance) but nothing as demanding as setting FFD in a camera.
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#10 Chris Millar

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Posted 02 January 2010 - 12:29 AM

hmmm,

off topic again maybe but just having an out loud thought - ok, so with tolerances like that what about thermal expansion/contraction ?

... which makes me wonder in turn what materials our micrometers and whatnot are made of in turn and/or are they simply just expanding/contracting by the same factor anyway ? :huh:

... and so if this is a consideration - what fun deciding the temperature at which to take the measurements.
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#11 John Sprung

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Posted 02 January 2010 - 04:15 AM

I did the math on that a while back, it turns out that at reasonable temperatures the thermal expansion/contraction is too small to be a problem. If you're working with car engines that may have temperature shifts of hundreds of degrees, it becomes an issue.




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#12 Tim Carroll

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Posted 02 January 2010 - 10:09 AM

Always keep my "52mm Standard" in the same place as where I am working on the camera, so it is always the same temperature as the camera I am setting the FFD on. And I sent my "52mm Standard" back to ARRI to have it calibrated.

The tolerance for FFD on the ARRI cameras I work on is plus or minus five thousandths of a millimeter, which is the equivalent of one tenth the diameter of a human hair. So yeah, it is a really tight tolerance. Where it really makes a difference is when shooting with normal to wide angle lenses, where the depth of focus is very shallow. If you only shoot with lenses in the normal to telephoto range, FFD is not as critical (as your depth of focus is greater).

Equally important is your ground glass setting, if you are focusing by eye. Or if you focus by the focus marks on the lens, then equally important is your lens collimation. It's all about getting the image sharp at the point where it strikes the film.

Best,
-Tim
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#13 Hal Smith

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Posted 02 January 2010 - 04:24 PM

off topic again maybe but just having an out loud thought - ok, so with tolerances like that what about thermal expansion/contraction ?

... which makes me wonder in turn what materials our micrometers and whatnot are made of in turn and/or are they simply just expanding/contracting by the same factor anyway ? :huh:


There is a metal alloy named Invar with a virtually zero temperature coefficient of expansion. It's what you use when any dimensional variation with temperature is REAL important. Some machine tool standards are manufactured using Invar. It wouldn't surprise me to learn that Arri's FFD gauges are Invar given how fussy Arri is about that sort of thing.

http://en.wikipedia.org/wiki/Invar
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#14 Paul Bruening

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Posted 07 January 2010 - 04:36 PM

Hi Paul,

PL has a nominal 52mm however I would depth measure the camera between 51.97 - 51.98mm. Hope that helps.

Stephen


I did the conversion between 52mm and 51.98mm. The difference comes out to .0008". Does this mean that you put the FFD somewhere into the film's layering by nearly .001"? Is that to favor the middle layer of emulsion?
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#15 Tim Carroll

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Posted 07 January 2010 - 05:28 PM

I did the conversion between 52mm and 51.98mm. The difference comes out to .0008". Does this mean that you put the FFD somewhere into the film's layering by nearly .001"? Is that to favor the middle layer of emulsion?


Paul,

You do want the focal plane to end up at the emulsion surface of the film or a little "into" the film emulsion. But that number is also to take into account the amount of "float" you get in the film as it moves past the gate at 24 fps. There is a different measurement for high speed cameras.

Actually, there is a different measurement for each of the ARRI cameras. It depends on the camera design, pressure plate, etc. But the variation from 52mm is a combination of putting the focal plane at the emulsion surface of the film or a little "into" the film emulsion and how much the film "floats" behind the gate when the camera is running.

And remember, your tolerance is not 52mm to 51.98mm, it's 51.98mm to 51.97mm. Or 51.975mm plus or minus .005mm (which is plus or minus .0002"). Again, what camera are you doing this on? It's FFD may not be 51.975mm.

Best,
-Tim

PS: Did a slight correction to my answer above.
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#16 Paul Bruening

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Posted 08 January 2010 - 01:13 AM

Again, what camera are you doing this on? It's FFD may not be 51.975mm.



Fries 35R3 (Mitchell GC) using Fries's Nikon lens board. Nikon's F-mount's FFD is 46.5mm.

I got the Artus shim stock pack yesterday.
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#17 Stephen Williams

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Posted 08 January 2010 - 01:54 AM

I did the conversion between 52mm and 51.98mm. The difference comes out to .0008". Does this mean that you put the FFD somewhere into the film's layering by nearly .001"? Is that to favor the middle layer of emulsion?


Yes, Yes.
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#18 Tim Carroll

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Posted 08 January 2010 - 07:13 AM

Fries 35R3 (Mitchell GC) using Fries's Nikon lens board. Nikon's F-mount's FFD is 46.5mm.

I got the Artus shim stock pack yesterday.


Sorry, I don't know the FFD for Mitchell cameras with a Nikon mount, probably someone else on these forums does. If you know the FFD of the Fries 35R3 in an ARRI PL mount, you can take that number and subtract 52, then add 46.5 and you would come out with the FFD for the camera with the Nikon F-Mount. Then take that number and use the average FFD tolerance of plus or minus 5 thousandths of a millimeter.

Best,
-Tim
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#19 Stephen Williams

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Posted 08 January 2010 - 09:34 AM

Sorry, I don't know the FFD for Mitchell cameras with a Nikon mount, probably someone else on these forums does. If you know the FFD of the Fries 35R3 in an ARRI PL mount, you can take that number and subtract 52, then add 46.5 and you would come out with the FFC for the camera with the Nikon F-Mount. Then take that number and use the average FFD tolerance of plus or minus 5 thousandths of a millimeter.

Best,
-Tim


51.97-51.98 is what I always set Fries Mitchells to with a PL mount.
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#20 Tim Carroll

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Posted 08 January 2010 - 10:02 AM

51.97-51.98 is what I always set Fries Mitchells to with a PL mount.


That would give you a 46.47mm to 46.48mm FFD for the Fries Mitchell with the Nikon Mount.

Best,
-Tim
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