Which configuration for dark field blood imaging? 0.6 nozzle and PETG possible?


i would like to build an OpenFlexure microscope but i am not sure which configuration/parts are best suitable, or sufficient for for this task?!

Then, anyone printed it using a 0.6 nozzle? Also my printer is better in printing PETG and ABS (depending on the size and shape) compared to PLA. As its more durable i mostly use PETG. Anyone did print using ABS or PETG.

Any advise, if possible with sourcing options highly apprectiated.

Thank you!

Welcome to the forum @nethead. I have only ever used a 0.4mm nozzle in a printer. I think the main body will be fine with a larger nozzle, and the base certainly should be. The optics modules and the condenser have some thin walls and thin gaps that may not work properly with a big nozzle.
There was someone who planned to print a microscope in ABS, 3D printing material - Request Help, they did not report whether it worked. As I suggested in that thread, printing the z-actuator from the upright version will be a relatively small part that should tell you whether the material will work.

For which version of the microscope to build, your thread title says you are planning dark field of blood films. There is not a well-developed dark field illumination system. There is an LED array system that was developed on the Delta stage to allow controlled illumination aperture. I cannot find it just now, it would fit either the Delta or teh Microscope bodies. Bright field blood film imaging works well using either the Openflexure Microscope or the Openflexure Deltastage with the high resolution optics version and a 100x RMS microscope objective (oil immersion). There are some blood film images on the Openflexure web site. The Microscope (version 7.0.0-beta) is probably the best basis for what you want, rather than the Delta stage.

Hello William and thanks for the help.

Regarding the 3D print i will try printing using my 0.6 nozzle because so far i can print “everything” with it except printing hinges in in place and the like. I will switch back to 0.4 if required and will report back on the full printing process. As ABS and ABS+ shrinks about 1% i will try to print the whole setup in PETG.

I did read somewhere that there is a “fix” for the prusa slicer to not mess with the custom brim. Where do i find it? I am using a Prusa 3MKS. Which part to use for testing if the custom Brim works correctly or needs adjustments?

I did just find the stl configurator (great effort!) but its for the 6.0 version and it doesnt seem to support a 100x RMS objective. So how do i configure / select STLs for such an setup and how do i include the LEDs? Should i try to copy the LED setup from Delta stage into the 7.0 beta version? I can use openscad so i could give this a try.

If i understand it correctly RMS lenses do have standard dimensions, right?

I did find this research paper on using OpenFlexure for blood imaging btw. maybe of interest for some of the readers here: Fast, high-precision autofocus on a motorised microscope: Automating blood sample imaging on the OpenFlexure Microscope - PubMed . The OpenFlexure hardware setup is explained here Optica Publishing Group

PS: Great project!


@nethead the slice gap closing radius needs to be set in Prusa Slicer. The instructions link from https://build.openflexure.org/openflexure-microscope/v7.0.0-beta1/high_res_microscope/test_your_printer.html in the blue (i) box in the middle of the page. This takes you to https://build.openflexure.org/openflexure-microscope/v7.0.0-beta1/set_slice_gap_closing_radius.html. You don’t need to print anything to check it, just look at the first layer in the sliced model of the main_body.stl and make sure that there is a small gap between the part and the brim.

I would strongly suggest that you build the V7 rather than V6, despite the fact that it is still labelled Beta. The high resolution version I linked to above is the one that you want and has all of the correct STLs in the print the parts page. RMS objectives are standard, but there are a couple of different options in the standards. The first is whether they are designed for an 160mm ‘tube length’ or are ‘infinite conjugate’. The standard Openflexure Microscope parts are designed for lenses specified for 160mm tube length. The next is the ‘par-focal distance’, which is often not stated in listings on cheaper lenses. The most usual is 45mm which is what you need here, but there are some with 35mm that will not fit the standard V7 microscope. Beyond that there are various lens qualities - a Plan Achromat is what you want here. There are a few Forum threads on objectives, for exampe Unsure if Objective lens will work - Request Help - OpenFlexure Forum and Sourcing non-printed parts - General - OpenFlexure Forum.

I checked and the LED array holder is actually in the Microscope full set of STLs, linked from the first blue (i) box in the customisations (https://build.openflexure.org/openflexure-microscope/v7.0.0-beta1/customisation.html. So you can just print that part. However I did not find any instructions or notes on how to use it. They must be somewhere, @samuelmcdermott might be able to help there.

I have found the LED grid instructions:
https://build.openflexure.org/openflexure-delta-stage/v1.2.0/pages/LED_grid_illumination.html. It does need to go that close to the sample, so that the outer LEDs are at a large angle. The total power possible on the array is high, it is possible to melt the holder if you leave it on at high power apparently.

Note that the STL linked on that page is designed to mount to the old version of the illumination dovetail. The STL with the same name in the full list of V7 STLs will fit the much improved new illumination dovetail (STLs linked in eth previous post)

I realised that the answer to printing in PET is already available: in Kenya a project was turning waste plastic water bottles (which are PET) into 3D printer filament and printing an earlier version of the microscope: Schools Digital Microscope Project Trial Implementation Report (techfortrade.org)

I also found a couple of reels of PETG when sorting out my filament stock. So I set the slicer to PETG and printed a few test pieces - the leg test, an upright Z-Axis and a C270 camera lens spacer. As indicated by Prusa the PETG sticks really firmly to the print bed, even using the recommended textured print sheet. However the parts printed pretty well. The z-axis motion seems fine. The outer lens gripper on the lens spacer is a lot more flexible than in PLA, and it detached at the base as I was squeezing it around. This is surprising as layer adhesion is supposed to be better in PETG than PLA. The filament is translucent green, and in PLA I have found translucent filaments seem more brittle than solid colours. I shall try again, and the other PETG reel is solid black which I want for actually using a lens spacer anyway.

I have now printed a main body and feet etc to assemble a microscope. Because the bed adhesion is so good it is all printed without brim, which is great. The main body has smart brim in the STL anyway.

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Hello and thank you again, William,

i am only using PETG and ABS with my printer as i have problems with nozzle clogs when using PLA because of high humidity and temperatures where i live. A friend will bring me 1KG of carbon enhanced PETG next week so i can print parts which need to be stiff using this filament.

My biggest problem right now is sourcing the non printed parts. I did read up on lenses on this forum but i am still not sure which lense to buy.

This one has been confirmed to work but i am not sure which resolution i should buy:

In the thread about this lense you say that the 100x would require oil immersion and recommend going for a 40x magnification lense. Is this correct? Example:

(Sorry, i am still reading up on microscopes and how openflexure works)

Yes almost all 100x objectives require oil (Necessary to achieve high resolution). If you don’t want to use immersion oil use a 40x or 60x objective.


Thank you, Nico. I did just “google” for 10 minutes and couldnt find out if live blood images are typically made using oil immersion? Would i need an oil immersion setup with a plan 100 lense for dark field blood imaging? Or would be a 60 lense plus the raspberry cam resolution sufficient?

Specifically what are you trying to analyze in your dark field blood images. Depending on what your analyzing different resolutions may be required.


i had problems with payment on AlieExpress and then ordered the same lense from ebay. After ordering the seller mailed me saying that he hasnt the exact lense but this one, i am not sure what the difference means. Could someone tell if this lense can be used:

Difference is “Plan 60/0.80” versus “Plan 60/0.85”, which had been the lense i ordered. I did forget what the second parameter “0.85 / 0.80” actually is.

thx everyone.

The 0.80 or 0.85 is the numerical aperture (NA) of the lens, it is a number between 0 and 1 (can be higher than 1 for oil-immersion lenses). For normal lenses it is the sin() of the maximum angle of light that can be used for the image. This is part of what actually determines the maximum optical resolution of the system. For a lens which is otherwise perfect, a higher NA gives a higher resolution as long as the NA of the illumination is at least as big. There will not be much practical difference between 0.85 and 0.80 NA, any differences in the actual optical quality of the lens are likely to be more important - how close to a perfect lens with that NA have they got.

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Hello William,

the objective lens i did order from Ebay did arrive but i forgot to order the ThorLabs AC127-050-A or comparable. Anyway, i started drying my filament(s) and did do the test print. Looks ok but i dont understand how the flex must work on this part? Its only the topmost part which should flex or the whole testprint?

Regarding the extra flex on the lense gripper i will print this part with a PETG/Carbon mixture. Should make it more stiff. Alternativley one could use a different infill pattern and / or more infill? Then, are the stls available without the custom brim as it might not be needed with some of the parts when using PETG?

Question: Should i start documenting my build here or open a new thread?



Hello Nico,

i would like to regulary (once per month) check the blood of friends and family for

  • Parasites
  • Fungus
  • Indications of Metals
  • Graphene-Oxide Flakes
  • General shape of blood cells



For theleg_test.stl the main point is that it should print without the top part failing to bridge over between the two vertical legs. If that works it is representative of the parts of the main body. If you want to look at the flexing mechanism, the leg_test.stl has two stiff vertical legs and two stiff horizontal bars in a rectangle. The top and bottom bars are connected to the vertical legs by thin sections. These are the flexure hinges and they allow the corners of the vertical rectangle to flex so that the rectangle becomes a parallelogram, which has the effect of a sideways movement of the top horizontal bar relative to the bottom one without any rotation.

My comment about the lens grippers is not really indicating a problem with stiffness. I was just playing with it too much because it was flexible and fun, and then it broke. It should be fine if just used as intended as a lens gripper, indeed I think it is probably better a little more flexible than PLA.


the top piece of the leg-test flexes but the verticals legs close to zero… So the next Test-Print would be the upright z-actuator, correct? And shlould i use the upright version or the regular, high resolution version (v7.0.0-beta1) for the final print?

Regarding PETG adhesion to the printbed: I am using the standard smooth, magnetic steel sheet. If adhesion becomes too strong i just swipe my fingers over the print area. Works like a charm.


Here is the testprint of the z-actuator of the upright version printed with 0.6mm nozzle using 0.2mm layer height and PETG filament. The printer shows some underextrusion and i had a blob of the last used carbon enhanced filament coming out mitprint. I probably have to change parameters for overhangs somewhat like more cooling.

Its not one of my best prints but it seems functional. What should i exactly check / measure?

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That looks fine. The only issue with slightly untidy prints is the dovetail on the front of the z-axis that mates with the optics module. If it is rough it does not fit as well. However you don’t need the module to slide after it is fitted so it will be OK.

When you get to print, go with the version of the microscope that you wanted, the high resolution version. The web site build link to v7.0.0beta1 is now a little behind developments. Unfortunately there is not a ‘nightly build’ link for the current latest version. It is probably useful to look at the threads on motor controllers for the new versions of the microscope stand and electronics drawer, particularly if you are planning to use Sangaboard v0.3 or v0.5 which do not fit properly in the v7.0.0beta2 release of the stand.

Sangaboard v0.5 now available - General - OpenFlexure Forum
How do I connect Arduino to stepper motors and get code - Request Help - OpenFlexure Forum

A version of the documentation with recent improvements in the parts and instructions up to July is currently at https://openflexure.gitlab.io/-/openflexure-microscope/-/jobs/4729744562/artifacts/builds/index.html This is not a stable link, it will go if we make any changes to that draft version. It has also not gone through the checks that we would do for a release so there may be unknown issues. For the high resolution version the only important changes I think are in the stand, and if you are using the 5mm LED work-around there are changes in the illumination module There are some changes in the instructions that should make them clearer.

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One more question: With a 0.6 nozzle the brim doesnt touch the model. This should be fixable by experimenting with slightly higher “Slice gap closing radius” settings?

The slice gap closing radius on Prusa Slicer sets whether the two parts are considered as separate or whether the gap is ignored and the parts are joined up. It will not change the nature of a gap. I have noticed that more recent sliced parts on my Prusa have more aggressive settings for avoiding elephant’s foot’ on the first layer. Even for a part with straight vertical sides the first layer in the slicer is noticeably smaller. Those settings will be somewhere else in the slicer. However with the excellent adhesion of PETG a brim is not really required, so I would just print it as it is.