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.