3D Printable, Seamless, Friction-fit Lens Gears for Follow Focus

Working with digital cinema and motion-control has given me an appreciation for Cine Lenses With Gearing On Them. Working in a reality where things cost money keeps me appreciating Stills Lenses With No Gearing But With Less Numbers On The Price Tag. Adding gears to stills lenses has traditionally required relatively expensive/invasive modifications, or compromised solutions involving bolts, cable ties, or other fiddly things.

Last year I figured out how to generate arbitrarily-sized gears for my selection of lenses, changing the internal diameter of each gear by 0.5mm at a time until they fit each lens perfectly.

All the while thinking, “if someone went through this process for a wide range of diameters and shared the designs, everyone’s lenses will get better, forever!”

My process was time consuming though, with multiple steps in multiple programs required for each size. Not conducive to creating hundreds of models that weren’t directly useful to me. Eventually though, the right confluence of technologies seeped into my brain, and I taught myself enough OpenSCAD (“The Programmer’s Solid 3D CAD Modeller”) to build off an existing script to create gears designed specifically for follow focus systems.

This project used to be hosted on Thingiverse, but unfortunately someone used a patent to have it removed, even though I had created my lens gears before their patent was registered. So I’m bringing all of the Thingiverse information back over here to my blog.

Following are detailed instructions on measuring lenses and printing appropriate sized rings. If your lenses have protruding bits, I’ve come up with a solution using split spacers to let an appropriately sized gear ring fit over the sticking out bits, but I’ve been manually creating the spacers thus far. It shouldn’t be too time-consuming to release an OpenSCAD script to make spacers though, if you’re interested, get in touch.

What’s going on here?

Convert your non-geared camera lenses to work with follow focus gearing. 50-100mm diameter in 0.5mm steps. OpenSCAD script to generate your own!

There are some great lens gear projects on Thingiverse, and plenty of inventive commercially available lens gears. Many of them require bolts, zip ties or other hardware though, which gets in the way of everything and also prevents full 360º rotation, which is super useful for many stills lenses which don’t have hard focus stops.

But wait! Having a 3D printer means you can print custom things exactly the right size for your stuff, as long as someone has taken the time to design a right-sized model.

I’ve uploaded lens gears from 50-100mm diameter in 0.5mm steps, and included the SCAD script if you need something tiny/huge/weird/awesome. Thanks to help from sveltema it is also enabled in Customiser, so you can generate a gear between 3-200mm internal diameter, and up to 60mm thick!

How do I use them?

Download the project .zip file (12.36MB, dropbox link) and unzip. It contains 100 pre-generated lens ring STL files and the OpenSCAD script if you want to make your own custom ones.

Measure the diameter of the focus ring on your lens. I use digital callipers for maximum accuracy, but a ruler, a piece of string, and some math can also get you in the ballpark.

Example: Nikkor 50mm F1.2 focus ring diameter = ~68.3mm

Multiply by shrinkage factor if needed. Different materials shrink when cooled. ABS by 2-5%, PLA by less. If you print something precisely sized to your focus ring it probably won’t fit. If you don’t want to do SCIENCE just add 0.5-1mm for your first test print.

Example: 68.3 x 1.02 = 69.666mm, rounded = 69.5mm. Download lensgear_69.5mm_94t.stl for printing.

Optional: Calculate number of teeth required & choose gear thickness.
If you’d like to use Customizer you can choose arbitrary teeth numbers until the gear looks about right, or if you’d like gears with a specific outer diameter (perhaps you’d like a matching set with common diameters for all your different lenses?) you can use a calculator to figure out how many teeth you need. Lens gears are sized “Mod 0.8”.

Thickness is the measurement of the band contacting your focus ring. Perhaps you need an extra thick gear because the focus ring on your cool antique lens moves in and out?

Example: 80mm outer diameter = 98 teeth. 15mm thickness looks super cool.

Make some test prints. When finding the right size I generally stop my test prints at around 20% completion, which is enough to test for fit without wasting time and filament. If you stop too soon you’ll have to deal with the oversized bottom layer of squished filament, so let the print go for a couple of mm high so you can test the actual fit on your lens. If it doesn’t fit, there are plenty of other sizes to try!

Example: 69.5mm, won’t go on! 70.5mm, doesn’t grip. 70mm = perfect.

Sand and file your perfectly sized gear. I generally remove the squashed bottom layer, which adds a little lip that prevents a correctly sized gear from sliding all the way on to my focus ring. Scraping with the blade of a pair of scissors is generally enough to get rid of this.

Apply to lens. If it’s the right size you’ll require some patience to gradually work the gear on to your focus ring. Brute force shouldn’t be necessary though. If you think you might need a mallet, try going up 0.5mm in diameter.

What about weird shaped lenses with protruding greebles?

If your lens has too much in the way of AF/MF selector switches, knobs or protrusions, you might have trouble getting a correctly-sized gear to fit slide over them. To fix this I’ve been using a two-piece solution:

• Gear internal diameter is sized to fit over the obstacle.
• Spacer printed as a split cylinder, allowing a tight friction fit.

It’s a couple of extra steps, but it works just as well as a one-piece gear if you get the diameters correct.

I’ve been making the spacers in Tinkercad, but if there’s enough interest I’ll whip up a quick script that’ll allow people to generate custom spacers as well.

How well do they work?

I’ve used gears just like these for years. They work beautifully, and my ABS ones are yet to show any significant wear. They also look much more professional than having gears zip-tied or bolted to your lenses.

Print Settings

Rafts: Doesn’t Matter
Supports: No
Resolution: 0.2mm
Infill: 20%

Notes:
I generally use 2 shells and keep the gear profile relatively thin, so infill doesn’t really get used. If for some reason you need thick gears that need to stand up to lots of punishment from heavy lenses or vicious focus pullers you may want to increase the shells and infill.

How I Designed This

Due to differences in material shrinkage (ABS shrinks more than PLA, for instance) you can’t really say “a 70mm diameter gear will fit all Nikkor 50mm F1.2 lenses.” So I’ve been using Inkscape/Tinkercad to manually design gear models whose diameters were stepped by 0.5mm increments until I found sizes which perfectly friction-fit my different lenses. All the while thinking “a complete set of these covering a wide range of sizes would be super useful for the filmmaking community”.

Eventually I found GregFrost’s Parametric Involute Bevel and Spur Gears script, and taught myself enough OpenSCAD to modify it to just produce gears with the correct tooth pitch for standard follow focus systems.
I was manually sanding off the sharp edges of my gears, so I also modified the design to bevel off those pointy teeth that snag on your camera bag/delicate human flesh.Support Jaymis making cool stuff!

I’ve been working in various nerdy aspects of film/video/live visuals production for a decade.

Recently I’ve decided to go solo to work on more of the projects that I believe will help filmmakers and creative video people make better stuff.

This is the first thing I’m releasing. If it helps you complete an awesome shoot, streamlines your rig, or saves you a bunch of cash, maybe you’d like to give me some gold coins? Or otherwise support the creation of future nerdy filmmaking tools? If so, there’s a button for that:

Updates

2016-01-05 – Updated instructions for Customizer / Diameter Calculation
jlevie01’s comment made me realise that I’d written the instructions before Customizer was enabled, so they assumed you’re just using one of my pre-made STL files. Added a couple of extra steps for those generating custom lens diameters/thicknesses.

2015-11-19 – Project/OpenSCAD added to Github.

2015-11-18 – Posted on Hackaday!
3D Printed Lens Gears for Pro Grade Focus Pulling. Thanks Hackaday.