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Lens Gear for Follow Focus - Seamless Friction Fit for Lenses 50-100mm diameter and beyond!

by jaymis, published

Lens Gear for Follow Focus - Seamless Friction Fit for Lenses 50-100mm diameter and beyond! by jaymis Oct 15, 2015

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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?

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 over a year. 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


Doesn't Matter








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, please get in touch.


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 - Customiser enabled. Code on Github.

Customiser enabled thanks to assistance from sveltema
Project/OpenSCAD added to Github.

2015-11-18 - Posted on Hackaday!

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LOVE THESE RINGS! Thank you, thank you, thank you!

My only comments would be if you could make them a couple mm thicker. They feel a little flimsy right now. I wish I had the know how to do it myself but I don't. Thank you again for these!

Once they're mounted on a lens, they're pretty robust. I've had a couple of them in use for 4-5 years now, and they've taken no damage.

If you'd like to make your own custom ones though, you can use the Customizer and change the parameters yourself!

This is great! I've been wanting one of these rings without the cost of an arm and leg. Designing one from ground up in cad is too much when this is available. Going to print one and play with.

Currently "gearing up" to cine-mod a couple of my vintage Konica primes. Just gotta get my hands on a set of calipers so I can get the appropriate measurements before I have a buddy print them, but I cannot wait to put these on my kit. In the meantime, I have some aperture de-clicking to do.

Hi there! I am looking at the scad-file and I'm not able to adjust the teeth height. I mean the distance from the outer edge of a single tooth down to where it meets its neighoring teeth. Can this be adjusted? Thanks!

Just made a gear wheel http://www.thingiverse.com/thing:2171841 so rings may work with the 12mm rod follow focus http://www.thingiverse.com/thing:565421

It seems though wide lens will not work with it so the rod adapter must be redesigned for wider lens and more travel

Follow focus gear 0.8 MOD for seamless lens rings
focus follow for 12mm pole camera rig

That's so great! 0.8 MOD seems to be the standard for Follow Focus, so that'll let the printable system work with many cinema accessories and lenses that have integrated gearing!

I'm completely new to 3D-printing so please apologize a maybe stupid question:
PLA is not flexible, right? So why can these belts fit to the focus ring but don't slip? If they are too small i have to use force to install them but if they are too large they slip? Do i have to glue? (i don't think so)
Thanks for enlighting me.

PLA is somewhat flexible. So is steel :)

They mostly fit because lens focus rings generally have rubberised grip material, so you can gradually ease the printed ring over the grip.

I've had a couple of lenses without rubber grip though, and they still worked fine. It's all about getting the right internal diameter.

Thanks for your reply. So I'll just give it a shot and try to figure out the right diameter. :)
Thanks for your work and for sharing the project!

What is the servo pictured? Thanks!

Thanks. It's not clear on the page; what drives it? PWM?

That's not a servo, just a manual follow focus: https://en.wikipedia.org/wiki/Follow_focus

These gears do work well with electronic follow focus systems though. I have one mounted to a stepper motor for super slow, accurate timelapse focus pulls.

I'll have to try one of your gears. I found an online 0.8mod gear generator that gives .svg files, brought that into Tinkercad and extruded it to half an inch. Put a cylinder in the center to remove the material needed, then subtract cylinder from gear. Trying to print on my Da Vinci Pro in ABS, but the tooth profile looks very wrong. This makes me ask, what size nozzle are you using? Mine has a 0.4mm nozzle and it looks like it is too thick.

I've got an 0.4mm extruder. I've done the SVG into Tinkercad thing in the past - I had issues with scaling, which is why I ended up using OpenSCAD.

Thanks, I'll have to try your files and see if they print better.

I printed one of your smallest gears and it is definitely a better fit than the gear I made with SVG to Tinkercad, the teeth from Tinckercad are way too fat. I think it is the slicer trying to fit all the way out to the sharp point where yours look more like the point has been truncated for printing (or maybe just designed correctly in the first place). That said, they are still not the same as the gears I cut on my mill, but at least yours fit better and I would consider them a workable design where the SVG to Tinkercad is not what I consider workable. The Tinkercad gears would be functional most of the time, but if you get an "off" gear from the follow focus, it may not mesh well at all.

I did find that Fusion 360 has a limited function involute gear generator included for free, it will do "imperial" and metric gears. I just hammered out a rough test and it's pretty easy to produce a gear, but I need to go back to my gear specs. to adjust a couple of variables. The big thing that I see with Fusion is the ability to put in some backlash, your OpenSCAD design probably has that as well. Going to print one after I get it set so I can compare to your gears before I print them for real lenses. I have a few FD lenses that need gears right now that I want to get finished. Cutting gears takes me about 2 to 3 hours each gear (raw material to finished gear) then heat and mount on lens (shrink fit). I'm hoping I can cut this to half an hour in CAD and printer prep, then a couple hours of doing something else while I wait for each gear to print. I don't do a lot of them, but it would be nice to have a "faster" method for each time I need to service a lens and need to cut the gear off.

Hoping to print in PET.

FYI, when cutting on the mill, the tooth profile is determined by the cutter used. Different cutters for different size disks (number of teeth). The backlash is set by the depth of cut, deeper than spec. provides more backlash. With the cutters the really big job is cranking the disk around to each tooth, then moving the cutter through the material. Big 120 tooth gears take a long time with a lot of motion. I haven't cut any smaller gears than 96 tooth which is mostly what I want for my FD lenses (about 78mm outside diameter), makes a nice size compared to the 77mm (80mm outside) step up rings that I'm standardizing on.

Here's a thread on the gears I've been cutting:


Thanks for the update Greg. That's really interesting stuff!

I'd suggest that the issue with SVG to Tinkercad is more likely to be that a gear parameter was off. If you change the "pressure angle" that will make the teeth seem fatter or thinner. Pretty sure lens gearing has a 20º pressure angle (that's what I ended up using, at least).

I've used these for ages now, including with motion control robotics, and have never had any issues with skipping or meshing. They won't be as robust as something milled in delrin, but for the price and speed of fabrication I'm pretty happy :)

Hi I am looking to make a set of these for my lenses but would prefer they all have same outer diameter so same number of teeth

how could I go about creating them?


Sorry Stephen - missed this comment at the time.
You can use the Customizer to make your own versions with whatever number of teeth you like. Figure out the teeth number for your largest diameter ring first, and then just change the internal diameter for subsequent rings.

Jaymis I love your work. Using Customizer I was able to create rings with a common outside diameter for most of my lens set.
But I have a couple that have larger diameters front and back of the focus ring. Reading your comments i wondered if you ever made the split ring idea availible on here?


Jaymis I love your work. Using Customizer I was able to create rings with a common outside diameter for most of my lens set.
But I have a couple that have larger diameters front and back of the focus ring. Reading your comments i wondered if you ever made the split ring idea availible on here?


Never made the split ring happen Stephen. Mostly because it's really easy to make them in Tinkercad. I've just shared a project that has a "partial angle tube" shape generator you can customise to your liking:


Probably require a Tinkercad account to edit that, but it's pretty easy to do, and Tinkercad is awesome if you haven't tried it before!

Works perfectly for me, thanks a lot !

this is genius!! thanks for making!

Apologies for such a novice question here folks, but I'm curious about the methodology for designing a ring in Customizer. In particular I'm confused by the "number of teeth" variable.

Lets say I've got a lens with a 60mm barrel then I would set the "Bore Diameter" close to 60? If I want the overall outside diameter of the ring to be 80mm then I set the "Gear Thickness" for 10. Where does "number of teeth" come into play? Obviously we want the gear pitch to remain at 0.8, but then shouldn't the number of teeth be calculated automatically based on the other two variables?

Thanks so much!

That's a great question actually, which I kind of glossed over in my instructions.

The Gear Thickness parameter controls the thickness of the band which contacts your focus ring. Not the difference between inner and outer diameters of the gear.

The outer diameter of the gear is controlled by the number of teeth. You set the number of teeth rather than the diameter, as your chosen diameter may not add up to an even number of teeth.

You can use a calculator to figure out a gear diameter: http://scriptasylum.com/rc_speed/gear_calc.html

In your example, 80mm gives you precisely 98 teeth! Lucky choice.

That's amazingly helpful! Thanks so much for the reply. I see now that I play around with the customizer that "thickness" is on a completely different axis from teeth and inner bore. Makes complete sense!

Jaymis -

Just had the gears delivered from Shapeways.com - delivered 4 days ahead of their promised schedule! Initial thoughts... damn, that was easy! I've ordered 4 different sizes because it's hard to measure the tolerances and account for materials shrinkage. I figured I'll try different colors too to see what looks OK while I was at it. Well, 2 of the gears fit perfect, just snug enough to barely slip on without any play. One's too big, one's too small so I can sand that one down a tad. At $7.35 a gear it's a flipping no brainer!

Fit and finish seem perfect with a slightly coarse feel to it. Matches to my standard pitch gear roller perfectly. Durability remains to be seen, but appears to be solid from my initial assessment. I made the diameter 15mm and it's ideal - prefect width to cover as much of the focus ring as possible without covering the distance scale.

Thanks again for sharing this with everyone, well done!

I've never ordered anything practical like that from Shapeways. Glad it worked well! That pricing is pretty compelling. Which material type(s) did you order?

Your make looks lovely. I really should use some more exciting colours rather than printing all my gears in boring black.

Lens Gear for Follow Focus - Seamless Friction Fit for Lenses 50-100mm diameter and beyond!

Jaymis - this looks like it just might be the ticket for my Zeiss Loxia gears! I don't own a 3D printer yet (suspect most people don't, lol) so I'm going to try and get these printed through Shapeways.com using their "strong & flexible plastic" material. My question to you is on the shrinkage... the Loxia lens diameter is 62.1mm... suggestions the size I should request? Thanks a bunch!

I've never had anything precise/mechanical printed through Shapeways, but their "designing mechanical parts for 3D printing" page says that they account for shrinkage when they make their prints, so it should arrive to you with correct dimensions:

That said, tiny tolerances make quite a big difference to fit with these gears, so a way to approach this might be to use Customizer to make a couple of different, very thin (maybe 1-2mm tall) test versions of slightly different diameters, check which one fits correctly, and then get the final one made.

Otherwise, err on the side of slightly too small, you can always take to your print with sandpaper!

Fantastic, placed my order with them based on your recommendations. Happy to report how this turns out. Thanks again for sharing your design!

jaymis, I edited your file to make it work with customiser.
What I changed:

  • editable variables in upper case
  • moved editable variable comments
  • added (random) ranges to editable variables
  • moved private variables and main gear module to near bottom of file.

The file I made if just the same as yours with some random range settings on the editable variables, so I didn't feel that it was right to publish it as a remix. Feel free to download the edited version to see what changes were needed:

ps you might want to consider removing the assign calls to get rid of the compiler warning

Wow. Thanks so much sveltema! I have a version that I was trying to get working with Customiser, and it seems I got pretty close. Thanks for the tutorial in Customiser-making-work.

I've changed the variables to allow some wild sizing variation (that will still generate valid gears) beyond the ones I've already generated, now people can make tiny lens cogs or ridiculously big, thick lens bracelets!

Customiser enabled, and I'll add the OpenSCAD to github so others can make improvements.

Glad to be of some help and keep up the great work!

The project is now featured on the Thingiverse homepage and in the Customizer collection! Thanks Sveltema!