Monday, June 19, 2023

2. The basics of Designing an Interface Between an Action Camera and Microscope

There are many imaging devices that can be successfully mated with one or more types of microscopes.

3D printed Smartphone to Microscope Adapters Are Available

While I have, over the years, been modestly successful at creating 3D printed interfaces between a smartphone and the microscopes I own,   Here is an image taken with a Sony Experia in 2017 using one my 3D printed interfaces.

Sony Smartphone to Wolfe Scope

However, the most brilliant design comes from

OpenOcular Smartphone to Microscope

Josue Gimbernard, the designer,  has developed an absolutely beautifully engineered product.  And he has done so purely for the purpose of enhancing the experience of owning and using a microscope.  His design is freely available on Thingiverse.

He suggests printing in PETG.  But, for a nominal fee ($22), you can purchase a printed version at his Etsy shop.

Believe me, it is well worth the $22 because an interface that works with just about any smartphone and microscope combination requires many parts and a great 3D printer.  Josue does a fantastic job of printing the pieces and assembling the most complex parts in PETG. 

I wholeheartedly endorse the OpenOcular device for mating smartphones to heavier microscopes.  I have one and admire both the design and the execution.  It has to one of the most clever 3D printed designs I've ever used.

Lighter microscopes can be mated with smartphones.  But, action cameras are a better, and easier, alternative. 

Action Camera Interfaces are simpler to design and Print

Due to their small size and light weight, action cameras require a far simpler interface and can be successfully mounted on even the lightest of microscopes.  There are just 3 parts necessary for a successful design.

Part 1: Camera Cradle  

Because the action camera will be oriented face down, there is no need for an elaborate mechanism for holding the camera steady.  We simply need to design an open cradle into which the camera will sit.

Part1: Action Camera Cradle

The basic measurements for this part are length and width, making sure that the corners that hold the camera in place do not interfere with any buttons on the top and sides of the camera.  We also need to provide a hole for any buttons located on the front of the camera.   The design above accommodates both the DragonTouch Vision3 and the Xilecam 4K 30fps camera buttons.  

The most critical measurement for the cradle is the center of the camera's lens.  It must be accurate to a tiny fraction of a millimeter to be used successfully.  The rectangular inset provides a stable way to glue the eyepiece connector base to the cradle. 

Part 2: Threaded Eyepiece Connector Base

The part of the interface that gives us the ability to accommodate a variety of microscopes is the threaded eyepiece connector base.

Part2: Threaded Connector Base

The inside diameter of the base must be at least wide enough to accommodate the camera's lens shroud.  It can be larger since the cradle, itself, ensures centering.  The inside diameter of this particular design exactly matches the outside diameter of the DragonTouch Vision 3 's lens shroud.  But, is slightly larger than the outside diameter of the Xilecam.

Since we must rely on glue (Gorilla Super Glue Gel) to join parts 1 and 2 and the actual eyepiece mount screws onto this base, we need to ensure that part 2 is securely locked into place.  This is accomplished using two tabs that resist turning the base as the eyepiece connector is screwed on and off.

The threads have a pitch of 1.6mm allowing us to adjust for differing eyepiece relief heights in very fine increments if necessary.

When joined together parts 1 and 2 look like this.

Cradle and threads Combined

With the cradle complete, we now have a platform that can be mated with an eyepiece connector for any specific microscope we would like to use.

Part 3:  Threaded Eyepiece Connector

There are three critical criteria for a successful microscope eyepiece connector for a camera interface.  The connector must hold tightly enough as to not move, it must automatically center the microscope eyepiece every time and it must place the camera at the precise location of the lenses eyepiece relief distance. Here is an illustration that shows what we mean when we talk about eyepiece relief distance.  From:

Eyepiece Relief Distance

Among my microscopes the eyepiece relief distance can vary as much as 10mm.  The MSK-01L, from C7 A Scientific has the longest relief distance.  I suspect that this is to make it easier for students to use.  For our connectors, we measure the distance from the face of the cradle to the face of the lens.  We use a distance of 23mm for the MSK-01L and a distance of 13mm for the Wolfe Student Microscope.

In addition to the differences in the eyepiece relief, we find a great variety of differences in the outside diameters of eyepieces.  While nominally fitting the same size lens tube (23mm), we find some lens diameters might range from 27.80mm to 28.85mm. One of my stereo microscopes has an outside eyepiece diameter of 34.2mm.  So, the range can be quite wide.

The OpenOcular solution to address the wide variety of sizes was to use an iris approach.

OpenOcular Iris Style Centering


It works very well.  But, it require a bulky and heavy mechanism.  To keep our design as light as possible, we have adopted a multi-connector approach.  We create a new connector for each eyepiece diameter / Eyepiece relief combination.  

Lens Connectors by Diameter and Eye Relief

Differences in Eye Relief Distance

 By relying largely on a revolve technique to design the connector, scalability is relatively easy.  The screw threads are exactly the same for each connector.  

The most difficult part is determining the exact eye relief distance when approaching a new eyepiece.  These connectors simply screw onto the cradle/ connector base combination.  Each size is labeled for quick identification.

Action Camera to Microscope Interface


The result is a very light weight camera attachment to just about any microscope.

The Tri-Wall Centering Technique

The most critical aspect of designing any interface to a microscope eyepiece is that of centering.  One of the lightest and most reliable methods we have found is what we call Tri-Wall design where we grip the eyepiece in a triangular fashion.

Tri-Wall Eyepiece Centering Technique

The outside diameter of the 3D printed eyepiece connector is a perfect circle.  But, the inside wall is a rounded triangle.  This results in some parts of the wall being thin and flexible while alternate parts of the wall are thicker and more stiff.  Three triangular shafts are attached at the thickest parts of the wall.  These shafts grip the microscope's eyepiece. 

This design lets us grip the eyepiece tightly while still providing flexibility when attaching and removing the holder.  The eyepiece is always centered.  The flexability allows us to use hard PLA plastic without damaging the eyepiece.  While either TPU (Flexible filament) or PETG can used, there is no requirement for perfect fit and strength.

Over the next few blog entries, we will provide instructions and videos that demonstrate the steps we take in Moment of Inspiration to create a cradle to attach an action camera to a low cost stereo microscope and a typical student microscope used in high schools.


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