Do film cameras still need pulldown mechanisms at all in this day and age?

[Geffen Avraham]

The Mitchell movement is a marvel of engineering, but it is a century old at this point. Today, we have made great advancements in precision motors that now enable things like motorized gimbals, that were simply not possible in 1924.

One can easily find stepper motors with 4096-position encoders capable of repeatable movement at extreme accuracy, used for micron-level precision in CNC micromachining. The cost of such motors has now dropped to only a few hundred dollars on the small scale.

This makes me wonder if it is not better, if designing a new film camera, to use a direct-drive high-precision stepper motor to advance the film 24 times per second. This could reduce the mechanical complexity and make one camera capable of shooting 2, 3, 4 perf by simply adjusting a dial.

My one concern is the noise, and whether stepper motors like this could be made quiet enough for sync-sound usage.

[Tyler Purcell]

Na, it's really not possible. The film needs to be physically held in place by something during the pulldown process. So a "claw" of some kind would need to be used no matter what. Otherwise, are you thinking of a rubber roller of some kind and perhaps a perforation detector? Let me tell ya, perforation detectors aren't accurate enough for stable image, especially on narrow gauge films. So that goes right out the window. Remember, can't have any light in there, so can't use lasers or anything that admits visible light. Stepper motors are also loud, so there goes sync sound quietness. 

The Penelope has a direct drive pulldown, using a very fancy motor which is silent. No reason you can't use that on most cameras, only it is a bit big for a 16mm camera. The reason it works on the Penelope is simply due to how much room is there, due to the design. They have an independent motor drive system, but the motor for the shutter is wicked small. Heck, the coils are wrapped in paper and plastic, it's very lightweight and fragile. They use a very simple timing disc that triggers all the motors from a single motor (the mirror shutter) and it's very easy to manage software wise. In fact, the design is beyond elegant. It's just unfortunate the Penelope didn't go anywhere, I think if it had and film cameras continued to be in production, other companies may have sprouted off over time and made lower-cost versions of what Aaton was doing. It is the most advanced motion picture film camera made, all be it, at a cost of being perhaps not as robust. It has pretty much everything you're looking for; easy to change pulldown, lightweight, dead quiet, direct drive, magnetically locked gates for easy swapping, very good PS-Technik optics, the thing is basically the best film camera made. 

[Andy Jarosz]

I've done a reasonable amount of research into this, and the challenge is acceleration. You can absolutely get super precise stepper motors that can go very fast--but they can't go from 0 to 100 in milliseconds. And with a film travel mechanism, a millisecond is a huge amount of time!

Another challenge is the simple fact that film is kind of fragile. Any mechanical interface needs to move the film in a way that doesn't cause a huge amount of friction or any potential for tearing or rubbing, as it could easily scratch or damage the film.

 

[Phil Rhodes]

I think the better question is whether film cameras actually need to have particularly high-precision pulldown in 2024.

Everything's going to be electronically stabilised anyway - witness the results people are getting even out of Super-8 these days.

Get the image on the film somehow. Where barely matters, within sane limits.

[Aapo Lettinen]

I think the only reason one could possibly have motivation to make a experimental movement like this would be to make a special experimental 2-perf camera. With 4-perf there is tons of affordable and better quality movements one can scavange from existing cameras (for example Konvas, Arri, Mitchell) and with 3-perf the price difference is too small compared to 4-perf to make a separate camera practical when there is tons of readily available movements and cameras in both 4perf and 3perf.

So only 2-perf I think and only if it has good enough perforamance to be post stabilized well enough to be on par with the no-reg-pin mos cameras. And needs to be affordable too because otherwise it would be cheaper, simpler, more practical and higher quality and probably less noisy to just make a mechanical movement instead.

I think the biggest limitation is that a electronic movement would not make sense unless it is exclusively 2-perf and then one could as well use a mechanical movement instead to get better end result and higher framerates

[Tyler Purcell]

5 hours ago, Aapo Lettinen said:

only if it has good enough perforamance to be post stabilized well enough to be on par with the no-reg-pin mos cameras.

It would be very bad stability and not correctable in post. 

[Robin Phillips]

I think a big thing is that if the registration is worse or the image is less stable in any way that compromises image quality over what currently is available, the concept is basically dead in the water. film, especially 35, is too expensive and needs to compete with digital in terms of sharpness and stability for VFX. And you just have to assume VFX is going to touch the images a camera will produce these days. 

this is just generally the problem with making a new film camera at all, it has to at least match the capabilities of the currently available cameras AND cost less than a good condition used one that still has a spare parts ecosystem. 

thats not to say I want to discourage anyone from building a new camera. But theres something to be said for examining how known cameras can have their build cost reduced and replicated and innovate where necessary vs building something a bit more revolutionary. 

[charles pappas]

This is what I was told - a stepper motor would not work due to the force of inertia:

Aapo Lettinen

• 
• Premium Member
• 
• •  3k
• Cinematographer
• Finland

• Premium Member

Posted October 24, 2020

  On 10/24/2020 at 12:28 PM, charles pappas said:

I appreciate the replies and know my post  sounded like I thought it would be easier than it is, and I realize that perhaps my ideas are not even possible or feasible.

Appo Lettinen: I envisioned removing as many mechanical components in the film drive system as possible, for cost and size reasons.  Also for cost and size reasons the LCD shutter.

Phil Rhodes: I don't know anything about LCD shutters except that they exist and seemed to be at least feasible for what I envision. 

Let me say a bit more.

I envision a drive mechanism incorporating a motor inside the cores of coaxial film reels which uses the indents of the cores to advance the film the distance between the film perforations. Whether this would be a stepper motor or some other I don't know - perhaps it could a constantly running motor with an circular on-off electromagnet turning the cores or some kind of pop-out ratchet turning the cores. 

The way I see it, there would be no film loops; instead the opposite.  The mechanism would rely on the film tautness to help with registration. In theory at least, if the factory tolerances of the plastic film cores and the distance between the film perforations  are good enough, then no electronic feed back loop, based on perforation sensors, would be required to control the motor. If that could be done, I would call that a "dumb," motor. (I know shrinkage of the film over time or expansion-contraction of the film due to temperature would have some effect, just don't know how much.)

I think the biggest issue  is ensuring no "play," in the film as there are no loops, so very constricting  guides in the film path would be needed, perhaps even a kind of four-sided tunnel to run the film through. In the worst case  of my "vision," if film "play," cannot be mitigated enough, a retractable pressure-plate, synced with the motor, would needed.  Adding to the cost and complexity for sure, but not less feasible than anything else here (I think).

The shutter would be directly in front of the feed-side of the two film reels, to help in mitigating film play, all the twisting of the film to get it onto the take-up core would be after the shutter.

Anyway, these are my ideas for a camera, ideas that seem to me to be doable and relatively cost-effective, but I would love for them to be debunked so I can forget about it. Conversely, if someone develops and sells this camera and makes any money, throw a bit into my hat please. 

 

 

 

Expand  

The film transport needs to be intermittent. Basically this means that inertia will ruin your plans: the moving film reels have so much mass that they cannot be fully stopped and sped up again to full speed 24 times a second. Probably this type of prototype would destroy itself in couple of seconds if one would build one for tests. Even if it would be sturdy enough to hold the enormous forces the intermittent operation generates, the film itself and the plastic core would disintegrate because of them. 

Additional thing would be that the film would still create loops when running from the reel to gate and back but those loops would be uncontrolled and would introduce massive registration issues which would be very difficult or impossible to correct in the gate with any mechanical system. 

Some high speed cameras use a rotating prism drum which enables using continuous film movement without the film stopping for each exposure. this type of cameras are not usable for normal standard speed cinematography due to image quality issues... and the film still needs to be mechanically linked to the rotating prism drum so one still needs sprockets to make the system work.

And yes, all the motors used for sync sound film camera use need to have a feedback loop which regulates and stabilises the motor speed, OR they have to be syncronous motors which are running at the same frequency than the incoming AC current alternates (like the old Mitchell motors and some older sound motors for various film cameras way before the crystal sync systems were possible to make)

[Aapo Lettinen]

theoretically it would be possible to use a electronically triggered mechanical registration pin to improve the stability so that it might be somewhat usable. It is very uncertain what the maximum fps would be with this kind of "solenoid registration pin" but I don't think it could do 24fps reliably and would likely jam very often ruining the film. Additionally super noisy and still more complex than a fully mechanical pin.

Such a pin could enable using some kind of very simple mechanical intermittent movement without compromising the shutter angle too much or even some kind of electronic movement though I am still sceptical a stepper motor would do as the heavy rotor would have so much inertia that it would either be impossible to stop it at correct points or it would outright fall apart from the excessive resonance caused by the very violent 24fps operating.

So maybe investigate the register pin option? it is not optimal and likely one would still want a mechanical movement rather than messing with electronics as mechanical would be much simpler and more reliable but the electronically triggered pin might actually work at least at low fps. It is not a good option but it is not that bad either, at least a very interesting project even if it would have horrible image stability... can't be worse than without the pin 😄

[Tyler Purcell]

Yea no way it would work. For a registration pin to work, it needs to fill the hole of the perforation. How can it do that, if the perforation isn't exactly in the right spot? You could make it a giant tapered pin, but even that would probably not work right. Also remember, registration pins generally only come out AFTER the shutter starts exposing the film, it's at the end of the stroke as the pulldown claw is retracting. A very basic spring loaded cam shaft that does this work on a motor drive, with some sort of plastic low-mass follower, is the only way to make it quiet enough. So now you have two systems, one that's doing the pulldown on its own motor system without even knowing where the film is. Another system, which is going to act like a hole punch when the first system doesn't work. 

Yea, no thanks. Plus, none of that makes the camera less expensive to manufacture. The pulldown system is not hard at all. Just straight up copy the Penelope design, it's excellent and very simple to re-create. Nobody would even know or care. Furthermore, with modern infinite ND systems, you could use that as a shutter. No need for a mechanical shutter and simply use a beam splitter and a video viewfinder. That's what we're working on FYI, it's no secret that's how you'd make a modern camera. The only thing you do NEED is a pulldown claw and a motor to drive the sprocket AND magazine. The days of a spinning shutter are over. Tho, the electronics may cost a tad bit of money. 

[Steve Switaj]

>> I envision (driving the mag) cores to advance the film the distance between the film perforations

Sadly, that's never going to work.

Rolls of 35mm film are heavy, and have significant inertia. It's already a known problem with some cameras that the film gets sloppy slack when the camera is quickly tilted and the rolls in the mag want to work against the motion.

Take a 200' short end, and palm it in your hand using your fingers to grip the outer edge. Now oscillate it back and forth an inch or so as quickly as you can. This gives you an idea of the inertia of even a small roll.

You're going to have to fight all that 24 times a second, precisely moving it forward and getting it all settled down again in a 0.019 second window. And if you're doing it in the middle of a 1000' roll you're trying to do it using control points effectively 100's of feet away (you want to drive from the roll cores to position the film you're pulled onto the outer layer, but you're actually driving the entire stack of film via friction between layers, and those layers will slip)

Then there's the physical properties of the film, like friction and stiction, which is going to vary by temperature, humidity, emulsion, hell, maybe the phase of the moon.

Almost every camera I've ever seen has the film handling split into two parts for this reason, with an intermittent movement at the gate, and a continuous movement (some sprockets) a bit further back. The sprockets are there specifically to insulate the intermittent from the supply and takeup rolls, which operate at a constant speed.

The intermittent, which has to have both speed and precision, is only handling a few inches of film at any given moment.

The loops take advantage of the flexible nature of the film to bridge the difference between the two mechanisms

 

>> Also for cost and size reasons the LCD shutter (which) exist and seemed to be at least feasible for what I envision.

Oddly, even if you could make it all work otherwise, this would probably be the factor that killed you.

Not because it's technically impossible - but because you will have to convince your DP's that is was OK photographically.

A normal shutter is a physical thing. It's in the way, then it moves out of the way. When the film is being exposed there is no question the shutter is uninvolved in the image, at that moment it's just a lens, some empty space, and then the film.

But an LCD shutter is an optical element that is in the light path at all times.

Its sitting between the DP's favorite $20,000 lens and his film, and it's doing... something... to the image. Something that he won't be able to see till dailies tomorrow. 

Is it adding diffusion? Is it adding a color cast? Is there some reflection or flare?  Is there a bit of dust on it - close to the film plane where it will leave a shadow?

At the very least, we know it will be interacting with the lenses as an additional optical element, and, at this level of performance, even a perfect optical flat will have to be accounted for in the lens design, or you will see chromatic aberrations, especially with wide or fast lenses.

This is why pellicle cameras never caught on outside some very narrow niches, even though they were very compact and quiet.

This is why anyone who owns a reflex Bolex will see a notable difference between a “normal” Switar lens and an “RX” Switar, which is calculated with the optical properties of a reflex prism in the image path.

Your camera will (effectively) be limited to using a list of 'approved' lenses or going out with a “buyer beware” disclaimer. And that will kill it commercially.

Edited August 8 by Steve Switaj

[Geffen Avraham]

I personally wasn't thinking of eliminating the continuous movement, only of replacing the pulldown which handles those few inches with a stepper.

"Transflective" mirrors are possible to make, which can switch between transparency and reflection 24 times a second. So no light would be lost if those were used, nor would the effect on optical performance be more than adding a clear filter, I think.

[Tyler Purcell]

1 hour ago, Steve Switaj said:

Your camera will (effectively) be limited to using a list of 'approved' lenses or going out with a “buyer beware” disclaimer. And that will kill it commercially.

Canon developed a reflex system that works fine. It works like a teleprompter. It's in the Canon EOS-1 RS, we have one. I've been studying the coating with some experts and it's possible to recreate. No special lenses required, works like a million bux and only loses around 1/4 of a stop according to the manual. Having shot thousands of pictures with that camera, I have never seen anything out of place. 

Now the LCD shutter is currently used as a ND filter on many digital cameras. I can't imagine it having any issues. It's also very small. Similar to the system used on active 3D glasses. It just needs to be extremely fast and very clear when not active. Not sure if possible to get both (absolute dark AND very clear for a decent price. However, if you added a standard half moon style shutter that  covers a high speed pull down, oh let's say 220 degrees? This way even if the LCD didn't work, you'd still get a good image. I don't think people need to get less than 220 degrees. 

All possible and would not affect the PL mount flange distance. 

 

[Tyler Purcell]

13 minutes ago, Geffen Avraham said:

I personally wasn't thinking of eliminating the continuous movement, only of replacing the pulldown which handles those few inches with a stepper.

What, like a sprocket intermittent in a 35mm projector? They tried that, didn't work. That poor motor would be doing all sorts of weird things, they aren't designed to start and stop something in 1/4 of a revolution and then start back again. It would struggle greatly to line up anything. Plus you'd still need some sort of registration pin system because the sprocket drive is too loose. So to hold it in place would take something special, like a registration pin. Finally, it wouldn't make the camera any cheaper. It would just make it not worth buying. It's one thing to do what we've been talking about and use a traditional movement system, but mixed with a few new toys like the LCD shutter for variable shutter speeds and fancy beam splitter and video assist. All of that is a bit more ascertainable in a lower cost 16mm form factor. Can't do a sprocket intermittent with 16mm, that's for sure. 

[Simon Wyss]

Summer Riddle

There was a 35-mm. film motion-picture camera featuring an intermittent sprocket and a pair of register pins. It also had a quick-change lens mount. What was its name?

 

 

[Tyler Purcell]

4 hours ago, Simon Wyss said:

There was a 35-mm. film motion-picture camera featuring an intermittent sprocket and a pair of register pins. It also had a quick-change lens mount. What was its name?

Yep, I don't remember, but it used a standard intermittent with the mechanical method of working, which is a lot easier to time. I think it was used for high speed photography as well. 

[Emiel de Jong]

The last generation of Kinoton projectors used stepper motors for the intermittent sprocket, even for 16mm... 

https://www.sprocketschool.org/wiki/Kinoton_FP_30_E

Their FP 38 ECII Reference model was built for quality checking prints, with better image steadiness than (most...?) mechanical projector movements could provide. So I guess it is theoretically possible to build a camera with this system. Practically possible is another thing I guess.

[Clark Nikolai]

On 8/7/2024 at 2:22 AM, Phil Rhodes said:

I think the better question is whether film cameras actually need to have particularly high-precision pulldown in 2024.

Everything's going to be electronically stabilised anyway - witness the results people are getting even out of Super-8 these days.

Get the image on the film somehow. Where barely matters, within sane limits.

Right, not to mention that one of the reasons to shoot film nowadays is to get "authentic" instability. If shooting film meant it looked like digital then why bother?  (I"m talking about only in the realm of art films and not huge budget films.)

[Andy Jarosz]

11 hours ago, Emiel de Jong said:

The last generation of Kinoton projectors used stepper motors for the intermittent sprocket, even for 16mm... 

https://www.sprocketschool.org/wiki/Kinoton_FP_30_E

Their FP 38 ECII Reference model was built for quality checking prints, with better image steadiness than (most...?) mechanical projector movements could provide. So I guess it is theoretically possible to build a camera with this system. Practically possible is another thing I guess.

I think the difference is projectors can be massive in size, allowing for huge motors with AC oomph behind them. Cameras are expected to be portable.

[Aapo Lettinen]

33 minutes ago, Andy Jarosz said:

I think the difference is projectors can be massive in size, allowing for huge motors with AC oomph behind them. Cameras are expected to be portable.

one other difference is that cameras have very different shutter angle requirements and the acetate film is fragile compared to the polyester prints stock used on projectors so the movement can't be as "rough working" as the projectors can manage with.

Projectors can be very, very noisy without issues whereas cameras cannot in most cases and blimping a camera makes it pretty much fixed whereas projectors are fixed anyway so one could as well build a "blimp room" around them.

----

Honestly speaking, the reason I don't particularly like threads like this is that they are only meant for discussing about crazy ideas on theoretical level and no one is ever going to build a prototype to actually test stuff and make a real project out of it. It is fun of course to imagine all kinds of crazy camera systems with 100perf pulldowns and such but I think it is not worth the effort if nothing actually working is built in the end and it all stays on the theoretical level.

the usual goal of these is not to actually build anything or shoot any real project or even tests. If one would want to just shoot 35mm that can be easily arranged (I for example have 6 konvases, can sell some if anyone needs a 35 camera. Tons of other options as well). If one would want to build a camera that could be done as well, but if wanting to build a camera you will exhaust all resources on the build and can't actually shoot with it then anymore (so you end up having a camera you spent years on making but have no money and time to shoot with it anymore. bad choice if wanting to actually shoot project instead of tinkering with stuff). If discussing about crazy cameras which don't work well /are not practical in real life then you are not even building a camera, you are just talking about stuff which will never be done. It is fun like mentioned but there is no end goal and from cinematography point of view it is pretty useless I think.

from engineering point of view, one would want to balance the use of resources and use the best working technology where it counts, NOT wanting to use less-than-ideal technology just for the sake of it. If the weird technology does not have clear benefits in the specific application then it is just bad engineering and total waste of resources to use it. The cameras are meant to be used for filming after all, if they are meant to just stay on the shelf never to be used one could just 3d print the outer casing and not needing to even add any movement or motor inside because no one would use it anyway 😄

[Don H Marks]

The fastest 35mm still cameras were still only about 9 to 14 FPS. 

[Simon Wyss]

12 hours ago, Clark Nikolai said:

one of the reasons to shoot film nowadays is to get "authentic" instability. If shooting film meant it looked like digital then why bother?  (I"m talking about only in the realm of art films and not huge budget films.)

Excuse me, no offence intended, but that is strange to me. How can the same persons insist on working with a “Bolex”, even praise its image steadiness, and then speak of authentic instability? Or pound on swiss craftsmanship, blabla, and use the camera handheld producing shaky trash? That’s what I experience every month.

I am certain that if the Lumière didn’t put the apparatus on a tripod, cinéma had not happened in 1895. Why does “art” film have to be tremulous? Such a moonshine

[Aapo Lettinen]

if specifically wanting unsteady image with "cool" dust specs, gate hair and scratches the easiest way is to use Krasnogorsk1 / Krasnogorsk2 or Kiev16U , preferably in non-CLA condition to get maximum effect 🙂

engineers have worked 150 years to get a reasonably steady image out of film movements and then the exact opposite is asked for 😄

---

I think the "pleasing unsteadiness" is more about the gate wave than the actual movement instability. so one gets this slight "rolling-shutter type but 8-directional" stretching effect on the image if the film gate + pressure plate combo is not super engineered and extremely well manufactured, perfectly adjusted and in great condition. The image "stretches slightly all over the place" even if it is not jumping up and down like with very bad movement. One can often remove most or all gate wave with rolling shutter correction tools but nowadays one could maybe add even more of it by modifying the gate and pressure plate to incorrect specs? 😄

[Aapo Lettinen]

yeah let's 3d print the gate and pressure plate at home out of the cheapest Chinese PLA with a 80 bucks printer, that should make the image more filmic for sure!🤣

( I remember purchasing the Lomokino kit back in the days. it was horrible crappy mechanism but I think it would be considered super filmic by today's standards... anyone need one? I could trade it for Arri or 10k of cash 🤣  )

[Steve Switaj]

On 8/11/2024 at 3:17 PM, Don H Marks said:

The fastest 35mm still cameras were still only about 9 to 14 FPS. 

I present the Hulcher 35 

      https://www.leitz-auction.com/en/Hulcher-35-Sequence-Camera-Model-112/AI-22-14420

Charles Hulcher was technician working for the NACA in the 50's when he developed a design for a still camera capable of taking quick bursts of photos. 

Hulcher eventually made a variety of models in 35 and 70mm, and they were quite popular with sports photographers well into the 90's, until they were eclipsed by digital cameras that could finally do more than a short burst

     https://www.theverge.com/2012/8/22/3260148/death-high-speed-film-camera-hulcher

Depending on the model, some of the Hulchers had frame rates into the 50 fps range.

I only once saw one up close, and never did quite understand how it worked. It was a 70mm version, the pulldown mechanism had a big swinging arm with a roller that would yank 8 perfs at a time through the gate, which apparently held the film there between pulldowns by friction alone (no need for register pins in a still camera)

How did it get up to speed? Did the motor spin all the time and the mechanism clutch in and out?  Was it driven by magic? Who knows? The Internet doesn't seem to have a lot to say.

Ironically, the Hulcher in the first link I posted (mostly because it has nice clear pictures) seems to have the exact kind of  sprocket drive we've been talking about.

Ah yes, yet another obscure camera. My kind of thread.