Goodbye bent paperclip!

Goodbye bent paperclip!


There are a couple of steps that people consistently struggle with when assembling the microscope, for good reason; they're pretty tricky.  Number one on the list has to be hooking in the elastic band - I've spent many hours myself jiggling around the bent paperclip tool in an effort to get the bands in, although I've assembled a lot now and probably have "the knack".

It's always easier to spot the problem here than to find a solution, but the latest development branch (v5.16) now has some progress - a different design of actuator where the elastic band gets hooked in from the bottom.  While I was at it, I changed the way the nut goes in, so it's inserted from the side rather than the bottom.  That means there's no more need to get the push-fit to work (which required strong fingers, and sometimes didn't work at all) in order to fit the actuating screw.  We've still got to test it before it's ready for the kits, but there's more details on the OpenFlexure Wiki and you can grab the STL files from the development branch on GitHub.

Once we've checked it works nicely, you can look forward to updated kits soon!

What magnification is it?

What magnification is it?

The number one question I get asked when I show people the microscope for the first time is "what's the magnification?" - and as anyone who's asked me this will tell you, the answer's not entirely straightforward.  Microscopes are often characterised by a magnification, a number telling you how many times larger they make things appear.  Typical laboratory microscope objectives range from 4x to 100x magnification, often used in conjunction with eyepieces that magnify the image further - often 10x but sometimes considerably more.  Sometimes (particularly in microscopes for home or school use) the product of eyepiece and objective magnification is quoted - this can be a high number, perhaps 1000x or even more.  Our microscope is digital - that means you don't use an eyepiece, and instead the second magnification step is performed by acquiring the image on a small sensor (usually a few mm across) and displaying it on a much larger screen.  Because the pixels on the sensors we use are really small, this can magnify the image 100x or more without losing quality.  If I'm pushed to give a magnification number, I will usually tell people that the resolution (i.e. the smallest thing you can see) of our basic kit is equivalent to a typical 20x microscope objective, though the magnification is closer to 50x.  The important quantities are the resolution (the smallest thing you can see) and the field of view (the area of the sample you can observe at once); for the basic Raspberry Pi kit these sizes are around 1 micron and around 280 microns respectively.  There's now a couple of pages describing this on the OpenFlexure Microscope Wiki.  I hope they make things clearer - suggestions and improvements are welcome!


First Cam Field Test – 5th July 2016

First Cam Field Test – 5th July 2016

It’s always an exciting day when you take your prototype into ‘the field’ for the first time. Although things may be working well in the lab, you never quite know what will happen when you take them into the real world!


We had decided that it was time for us to venture out and conduct our first field trial. As we had strong suspicions that the River Cam would be harbouring a few(!) bacteria, we thought that it would make an excellent first test, not least because we could then sit in Jesus Green and enjoy an ice-cream and BBQ at the same time!


We collected a sample by Jesus lock, and were surprised by how clear the water was. However, the first round of filtering left a very dirty filter, showing just how much particulate matter can go unseen in the water! We then filtered the water again to catch any bacteria, and transferred the bacteria to agar. So far so good (especially as the sausages were nearly ready...).

cam riveralex and Nalin


The agar plate was then placed on the microscope, allowing us to test our new incubator. Unfortunately, a few burgers and an Old Speckled Hen later we couldn’t see any growth using the microscope. It was a disappointment, but it was to be expected that something wouldn’t work first time - we just had to work out where the problem was!


waterscope team at camben and richard

Thankfully, after leaving the agar in a commercial incubator for a short while we were able to see growth down the microscope. This suggested that it might be that our incubator isn’t working as effectively outside as we had hoped. Now back to the lab to tinker with our incubator ready for our next field test!

cam river trial result

Using “proper” microscope optics with the OpenFlexure Microscope

Using "proper" microscope optics with the OpenFlexure Microscope

A commonly-asked question when I speak to people about the microscope is "can it do X?" for various different values of X.  Often my answer is that, while the basic model I'm showing you here can't, I have another version that can.  This blog post is about the other versions, and how to get hold of them.  First though, I'll list a few of the most commonly asked-about features:

  • Better resolution/higher magnification
  • Wider field of view
  • Use of a "proper" microscope objective
  • Imaging modes other than bright-field (e.g. dark field or phase contrast)
  • Fluorescence imaging
  • Motorised control of the stage position and focus
  • Upright geometry (looking down on a sample rather than looking up through the coverslip)

All of these things have been done with the microscope, pretty successfully.  however, not all of them are available easily.

Writing good instructions is hard, and despite putting a lot of effort into our instructions, it's still very easy to confuse people.  This is particularly problematic when there is more than one way to do something; experience has taught us that it's easier for everyone to pick a method and stick with it.  However, this makes it hard to include optional features, which usually affect one of the assembly steps in some way.  Consequently, I usually encourage people to get in touch if there's a feature they want, so I can point them in the right direction.  I'll save most of those features for future blog posts, but I'll add the instructions here in case anyone wants to use a real microscope objective instead of the Raspberry Pi Camera module's lens.

Better resolution, higher magnification, and wider field of view are all possible if you use a "proper" microscope objective.  There are designs on GitHub for a modified optics module that takes a 40mm focal length planoconvex lens and a conventional RMS-threaded microscope objective.  The "Large Stage" version of the microscope is needed to accommodate this (the small stage is not big enough to fit the larger objective into), and it in turn requires a different illumination arm.  The bigger microscope is denoted by an "LS65" in its filename/model number, meaning a wide stage that is 65mm high in total. I try to keep the STL up to date for those who don't have OpenSCAD, but the most up-to-date version will always be the OpenSCAD file; in microscope_parameters.scad you need to set "big_stage=true" to get the large stage version.  Then, open and compile main_body.scad to generate the microscope and illumination_and_rear_foot.scad to make the illumination.

We've settled on a 40mm focal length, 16mm diameter lens for the inside of the tube - this is necessary as otherwise we'd have to use the microscope objective at the wrong working distance.  I get ours from Comar - the 40 PQ 16 works nicely.  You should be able to push-fit the lens, and essentially push fit the objective too, though we usually screw them in to avoid crushing anything.

If you've tried this recipe, or if you'd like us to sell you a custom kit for it, do get in touch!

Product launch

yellow waterscope

We launched our first product, the Raspberry Pi microscope kit, as part of Cambridge Open Technology Week 2016.  We’re still improving the instructions and the design of a few of the parts, but it’s exciting to be able to supply kits so more people can build the microscope.  Pop over to our store to bag yourself a kit!