Ability to change the Objective Lens

Oh, Almighty Chair of the CCCCC, your immense wisdom has once again shown to be right on! It may be possible to run the cable on the side of the optic tower.

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Almost done. Long ribbon cable coming tomorrow. I will post pics when I am done.


You need some motors on there… (because why not right)

For my use case a manual version works best. A motorized version will only slow down the slide review process.

So my entire setup is complete and functional. It is really promising and I see a tremendous potential for the openflexure family of microscopes, yet it aches my heart to mention certain negative elements I discovered during my initial review. Please consider this review to be constructive criticism.

I was able to get a good image with 20x and 40x. The 4x was way out of range and did not work. Probably 10x is the lower magnification I will get with this setup. The 4x or 2x may some sort of tube adapter to make them closer to the sample?


The most difficult issue is changing the objectives. Each time you make a change, you must remove the glass slide from the stage and perform a full auto calibrate. This takes several clicks, and the worst part is that you lose the sample’s position. This one problem makes this version tough to use. This would necessitate an initial objective calibration, the storage of those values in the system, and the addition of a button to retrieve them whenever the objective is changed.

The objectives must also be held in position by some kind of clamp mechanism. In my opinion, the magnets are over-engineered. A simple flexure clip could be enough.

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For the lens distance it sounds as though you have some low magnification lenses with a different par-focal distance. A set of lenses with the same parfocal distance are designed to all focus in the same place relative to the shoulder on the RMS thread. This makes objective turrets work on normal microscopes. The Openflexure Microscope is designed for 45mm parfocal distance which is the most common now, but 35mm is also a standard and I have older lenses with all sorts of distances.

Your feedback on calibration is something that should be relatively straightforward to address in the software, but may not fit in the timeframe of the Openflexure Server v3 release. Server v3 is targeted at the microscope v7.0.0 release, which will not include swappable objectives at first. For a motorised swappable version you would need to save and retrieve the camera-stage mapping as well as the flat field camera correction. A motorised version could actually know automatically as soon as you move a little bit, by matching the image change seen with the available stage mapping files :slight_smile:.

For a better experience on manual operation, I would point you to the modified body that is available, linked from the thread Minimal manual version of the Openflexure microscope. The manual body should interchange with the main body in any of the other versions of the microscope, not just the webcam version shown on that thread. That version does not create the STL for a manual separate z-axis for the upright, but it could easily do so. Edit: The merge request now does include a manual version of the separate z actuator for the Upright version.

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Thanks so much for building one, and for your feedback - hearing what works and (especially) what doesn’t at this stage is immensely helpful! All notes gratefully received.

Indeed as you encountered and William notes, this is intended to be used with objectives of ideally identical parfocal distance to avoid considerable height changes between lenses. Particularly low magnifications would also likely start to run up against the limits of the usual OpenFlexure illumination. This is definitely something that I should make more obvious in its current form!

In intended operation there should be no need to touch the glass slide between lens changes at all; at most in my testing I’ve seen some minor flat-field correction changes between lenses, which can be minimised by careful assembly of the objective lens carriers. My general plan for software integration was to implement a saved per-lens calibration so there can be one-button calibration changes for lenses and lenses can be calibrated once during assembly to “set and forget”. Richard noted to me this would require some structural changes to the software settings manager, so this may take a little while to implement in a satisfying way.

Based on my own testing, I’m thinking it might also be useful to have some kind of “sanity check” present in the system to measure whether or not a new objective lens is correctly in position based on whether or not the expected field-of-view of the sample is in frame. If anyone thinks this would be pointless, or complete overkill, all opinions very welcome! I am biased by virtue of already having written most of the necessary code…

Daniel, I’m curious as to whether you have tried the ball-bearing and dowel kinematic mount alone - based on your pictures above, there are no dowels in your mount or ball bearings in your objective lens carriers (the hollows in the carrier for ball bearings are also intended to face downwards towards the dowel hollows when objective lenses are in place). Do you find the simple carrier shape sufficient for accurate lens placement, and do they hold in place well enough? We had opted for the metal-on-metal kinematic mount on the basis that it would be more durable over time than plastic-on-plastic contact, but there was also thoughts of a “pizza wedge” flexure carousel at one point.

The disc magnets are not strictly necessary for the kinematic mount, but I added them for their satisfying gain in stability and ensuring the objective carrier bearings are fully in contact with the mount dowels (and, best of all, they make a nice ka-chunk noise when objectives are placed correctly!). I speak as a physicist, though - if they’re no good for practical use, that’s that!

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Hi Freya. Thanks for the explanation about the objective distance. I “harvested” objectives from old microscopes at the hospital for this build. This should be an easy fix for me. Even so, I did not experience much problem positioning the objectives. It did move quite a bit during focusing due to the lack of an attachment mechanism which I managed to keep it in place with a small paper wedge. I did not try the ball bearing and dowel kinematic mount because I could not find the explanations on the website or which hardware to buy. The triangular shaped carrier is a brilliant idea and worked very well for me. Could a simple thumbscrew like the one used in the condenser arm work?


Well, it is almost magic time. I have got most of the things in the mail for the build. I noticed that the upright version is only hosting the basic optics setup whereas the more standard OpenFlexure build can support the high resolution optics configuration with the additional lens. I would like for my build to be the best that it can be. I have therefore ordered the 12.7mm diameter 50mm focal length doublet lens. Is there a way to integrate it into this build configuration? It seems as though all I need to do is remove the PI Camera lens and then insert the 12.7mm diameter lens at the right spot. Do I have that right? Seems like one could use a simple retainer ring to hold it in the assembly?

Sorry, I was silly and not looking at the correct instructions. Please disregard my above post. :frowning: