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DM1X too slow for massive high-speed pull. Ideas for next time?


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#1 Jared C. Rogers

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Posted 03 August 2013 - 02:12 PM

First time poster. Sorry if this is already a topic somewhere (couldn't find it in any search).

 

I like to think there is a solution to most technical challenges--not always an elegant one--but I'm still scratching my head about this one:

 

Shooting yesterday the DP wanted to do a 120FPS shot on a slider from about 9" (ECU eyeballs) to 4' (medium shot). We framed up on a 32mm Zeiss Close Focus Prime.  

 

I knew about it ahead of time, which was nice, and experimented with different calibration techniques to get the throw on the Preston to feel like a manageable pull.  

 

What I didn't realize was the DP wanted the whole thing to happen in ~1.5 seconds.  I quickly found out "on-the-day" that the motor simply couldn't catch up with the move.  Ultimately we had to slow the move down to match the speed and throw of the lens.  

 

Anybody know what we could have tried?  If the motor is running at its max speed, there's nothing left to be done, right?  I suppose an idler gear that could create a massive mechanical advantage between the motor and the lens could work, but it'd have to be custom and would probably introduce a whole range of new problems.  It's really the only option though, right?

 

I suggested switching to a 50mm (non-CF) prime and trying to match the frame size and hopefully achieving less barrel throw, but we had space limitations and the DP was more committed to the 32mm look than the speed of the move.

 

Anyway, I wanted to toss this challenge to everyone and hopefully get some ideas for next time.


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#2 Victor Lazaro

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Posted 03 August 2013 - 02:34 PM

What about making a larger gear for the motor if the lens is not too stiff that could work no?
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#3 Jens Piotrowski SOC

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Posted 03 August 2013 - 02:53 PM

Your hand and a speed crank should do the trick. If its on the slider, No need to use a Preston.
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#4 Jared C. Rogers

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Posted 03 August 2013 - 03:53 PM

Victor: That's the only thing I can think of too, but it'd need to be an idler since the motor's drive gear is not really setup to be enlarged.

 

Jens: I've used that technique for a similar shot a different job. It wasn't even close this speed though.  I suppose we could have tried it, but I'm pretty doubtful my hand could move that fast and maintain any kind of accuracy during the move.  The Zeiss Close Focus have quite the throw at these distances; I'm talking at least triple the rotation of a regular prime.

 

Anyone ever heard of using idler gears with focus motors?


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#5 Martin Stacey

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Posted 03 August 2013 - 05:14 PM

I wonder if the Axis1 could have pulled it off. Fastest system I've seen.
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#6 thomas-english

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Posted 03 August 2013 - 06:19 PM

The DM1X has come under criticism from the Pace techs for being too slow. The DM2 is a faster motor as well as a Heden. The DM1x is the torque ist out there though.

 

You could have put a bartech on there with an M-Motor. That would have smashed it out the ballpark for sure.  


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#7 Jens Piotrowski SOC

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Posted 03 August 2013 - 07:01 PM

From Preston website: The DM1X Digital Motor has the highest speed and power of any available lens motor. It is specifically intended to focus cinema lenses, allowing for quick focus racks on even very large zoom lenses.

That matches my experience with this motor.
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#8 Jerry Holway

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Posted 03 August 2013 - 07:14 PM

A larger idler gear won't change the speed; the motor needs a bigger gear if it is to move more teeth per rotation. 


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#9 Victor Lazaro

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Posted 03 August 2013 - 10:01 PM

A larger idler gear won't change the speed; the motor needs a bigger gear if it is to move more teeth per rotation. 

That's what I was saying, otherwise, you will need a "gear box" with two different gear sizes on one axis between the motor and the lens for it to work.

This is highly hypothetical, can be done, but might be much easier to custom make a gear for the motor itself, it's true that the DM1x would be hard to do that on, but a Heden motor could do the trick fairly well for the mod.


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#10 Jared C. Rogers

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Posted 03 August 2013 - 10:36 PM

Thanks for helping with my thought experiment everyone. I didn't realize Hedens were faster, so I'll remember that next time.  

 

Yeah, the idler thing is totally hypothetical, but also attractive in its simplicity; and I realize now idler may be the wrong term.  It'd have to be a small gear sandwiched against a large one so each rotation translated to more teeth. 


Edited by Jared C. Rogers, 03 August 2013 - 10:36 PM.

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#11 thomas-english

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Posted 04 August 2013 - 01:41 AM

I might be wrong then about the DM1x. I certainly was told this when deciding which to buy. dm2 or dm1x. With friction free lenses my hedens are definitely quicker. The DM2 is definitely more robust. 

 

Certainly the DM1x is faster with a stiff lens. Is this still the case with a friction free lens? 


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#12 Peter Hoare

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Posted 04 August 2013 - 06:59 AM

 

Imagine what it can do on smaller barrel sized lenses. Your hands cant keep up ;-) 


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#13 Chris Flurry

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Posted 22 September 2013 - 06:15 PM

Arri FF-3 2 speed knob with a speed crank. Or Panavision 2 speed knob. If that's still not fast enough make a tape stop on the lens (which I would recommend doing anyway) and use a piece of tape stuck to it self wrapped around the lens barrel and taped to it and pull real fast. But I'd think a two speed knob should do the trick.
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