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Ultra long slow duration zoom: lens, control system, modifications

Andrew Skalak

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I tried to search the topics here for a similar topic, but I have not been able to dig anything up.

I want to do a zoom that starts as a wide of a dining room from the next room over. As the scene plays out, I would like to zoom in very, very slowly, until I can end the scene in CU on a glass sitting on the table. I would like to have this move go for over five minutes, maybe even longer up to ten minutes. The only film I know of that has a zoom this slow is Michael Snow's "Wavelength," but from the version I have seen, that seems to have been shot on an older video camera with a sort of modified zoom rocker?

I will go in and do tests at a rental shop, but I cannot find any specs on the Preston site of what the slowest possible speed is for a microforce or similar. I am looking for a formula that tells me the minimum speed for degrees of rotation on a standard .8 pitch zoom gear, so I can then calculate how long a zoom could possibly go for on different lenses. I may also need the circumference of a given lens as well, as larger lenses with a fast stop are thicker and have many more teeth?

I am also wondering if there is a way to add an additional gear in between the zoom motor and the lens gear to "trick" the motor into spinning much longer while making less progress on the actual zoom, like a sort of transmission or how bike pedal gearing works. Does a product like this already exist?

Thank you!

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  • Sustaining Member

I think one issue you will have with doing this with a Microforce or similar manual motor controller is that if you keep the motor speed constant, then the zoom will appear to move faster and faster towards the long end of the lens.

Maybe that will be ok, but if you want the appearance of a constant zooming speed, then you’ll need to gradually ramp down the rotational speed of the zoom ring during the shot. In that case, I think you’ll need some kind of motion control rig where you can program the motor speed on a curve.

Or if you’re willing to risk a sore thumb, you could do it with a Microforce on the lowest setting and perform the ramp manually. Hopefully you won’t have to do too many takes! 

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you can also get a second wireless hand unit and use the wheel to control the zoom - it would be more intuitive for fine adjustments, and you can place marks on the wheel to time the zoom properly.

additionally, it would help with what satsuki mentions about apparent zoom speed, because you can slow down the zoom at the tighter end with more precision

you would need another person doing this (not operator or 1st ac)

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  • 3 weeks later...

Something else to keep in mind -- the teeth of the gear of your zoom motor/the teeth on the focus ring and how they mesh.  You want constant contact to avoid any micro stuttering as one tooth hands off to the next.  In theory, creating firm contact between your motor and the lens can solve this - but this relies on the barrel of the focus ring being perfectly round.  If it isn't, too much pressure will create problems that will be exacerbated by the slow zoom.

My recommendation:  Newer zooms will be in better shape with perfectly round barrels and cleaner teeth.  Also seek out a new gear for the lens motor you're using.  You could consider buying or even 3d printing a new one if you have access to that or know someone who can help you out.

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