Why do some cameras use geared rollers and some smooth ones?

Gergo Gosztolya · October 27

I've been looking at the film transport mechanisms in 35mm cameras, and started wondering why some cameras have geared rollers, where the gears engage with the sprockets, and drive the film forward (like most Panavision cameras, the Moviecam Compact Mk2, and the Arricam ST), whereas some others have smooth rollers that don't move the film, just guide it, and let the claw do all of the work (Arriflex 435, 235). So what are the advantages/disadvantages of each design?

The first picture I attached is the Moviecam Compact, and the second is the Arriflex 435.

Mark Dunn · October 27

The answer is design, and in the case of Arriflex, engineering genius.

The Arriflex movement is far simpler than the Mitchell movement on which the Panaflex and its like were based. It was designed as a newsreel camera that didn't have to be babied every day. It was good enough.

The 2c on which the 235 and 435 were based weighs 6kg. It takes 4 men to carry a Mitchell.

The Arricam was adopted by Arri, they didn't design it. I think the 35BL is a more conventional geared sprocket design.

Edited October 27 by Mark Dunn

Gergo Gosztolya · October 27

So in modern designs, adding geared rollers wouldn't have any advantages, and would just increase mechanical complexity and weight?

Dom Jaeger · October 27

All these cameras use the same basic concept of sprockets creating a fixed loop while the movement creates the intermittent motion.

The difference in design you‘re seeing is whether the sprockets are in the magazine, or whether they are in the camera. It probably comes down to mag design etc, but I imagine sprockets in the camera can be more easily sound insulated. Some of these design decisions also come from historical lineage, the 35-3, 435 and 235 kept the same basic mag design principles as the original Handkamera from 1937.

Gergo Gosztolya · October 27

I might just be blind, but I don't see where the sprockets are in the Arriflex 435 mags. It seems to me that the only parts engaging with the sprockets in the 435 are the claw and the registration pins (though I might be wrong).

I attached a picture of the Arriflex 435 mag and the Arricam ST mag (in this order, both 1000ft), and they look very similar mechanically.

Dom Jaeger · October 28

That drawing isn't showing the drive gear and sprockets.

Here's the page from the 435 manual descibing mag loading, where you feed the film into the sprockets and set the loop length:

435mag.png.0d616af9ee4e606e6bfb231d48a2bdf7.png

Tyler Purcell · October 28

As stated above, some cameras have the sprocket drive in the magazine, some of them have it in the body.

The reason they put it in side the camera, is that the sprocket drive CAN make noise, so if you put it in the camera body, connected to the movement (mid-plane), inside the self blimped camera, you can make lighter magazines without the need for much sound damping. You can also electronically dive the magazines, vs mechanical drive, which is a big benefit. Obviously the Moviecam and Arricam mags do have isolation mounts for the platters/motor assembly. However, they are a lot lighter and easier to load than the alternative. So it's a compound reason and unfortunately the mags are not compatible.

Aapo Lettinen · October 28

on Moviecam and Arricam the magazine takeup is electronically driven. No gear link between the magazine and camera body, just a electronic connector. Thus potentially eliminating tons of noise.

Yes it should be much easier to soundproof the sprockets and gears inside the camera body than on the magazine. Additionally the magazine doors are large flat-ish surfaces potentially generating tons of noise from resonances so one would like to try to eliminate resonance by reducing the possible sources of it.

Arri2 / 35-3 / 435 / 235 cameras and the 35BL cameras and derivatives have the sprocket drives inside the magazines. On MOS cameras like the Arri2 it simplifies the camera design and likely helps making the camera body more ergonomic and easy to load for it being originally made as newsreel / army combat camera. And the later designs like 35-3, the 435 and 235 needed to have magazine compatibility so they kept the same design despite having possibility to design new one.

There is also the third type of design, used on Mitchell-type cameras and Auricon and its derivatives like CP16 cameras etc. Those have very simple magazine design with only the film roll chambers and some plain rollers to feed film from and back to the magazine. The takeup friction drive is located inside the camera body, NOT in the magazine like on most other designs. a simple rubber or leather belt runs the takeup roll directly, the magazine just having the belt pulley mounted directly on the takeup roll axle with nothing between. All the sprockets are inside the camera body. This type of system makes the magazines really really simple and affordable but adds size and complexity to the camera body. If you need tons of pre loaded magazines then it may be really convenient to have cheap magazines available, you can buy 10 and load them all beforehand which makes it easier to work on the actual shoot. Threading these Mitchell-derivatives is more time consuming and precise but the magazines are super fast to load. The magazines are almost maintenance-free for having so few parts, thus having 10 magazines is not an issue. on Arris etc. one would need careful maintenance on each and every magazine including setting the takeup friction on each one