I recently decided to assemble and try the openflexure. The build was smooth and easy, everything worked and I was happy to see something on my screen and the illumination working!
Thank you for sharing your build. The objective and tube lens specifications look OK. The objective is achromatic, but not ‘plan’, which means that there is likely to be blurriness around the edge of the field of view when you do get the centre in focus.
The image that you have posted looks to be just a long way from focus. With a 40× lens the working distance is much less than 1mm. You need to have the slide placed with the object on the underside, do that it is close to the lens. These objectives are designed to view through the ~0.15 mm coverslip. They cannot focus through the slide.
It also looks as though you have some dust, or stringing from the print, in the optics module or on the camera. The white halo around it is from the lens shading correction which will try to compensate for the dark line. That kind of dust can be a bit of a pain to find and to get out, it will be very small.
Ah, that may be something different. What is the physical length of your lens, from the shoulder at the mounting screw to the lens? I don’t think it is possible to have the optics module that far down the mounting slot to be 1cm away from the slide. However there are two standards for an objective lens par-focal distance, the length from the shoulder by the lens mounting screw to the focal point. 45mm is the most common, and the Microscope is designed for that. There is also a 35mm standard. The listing that you linked to does not state the par-focal distance. If your objective is less than about 43mm long it is probably the wrong kind, unfortunately.
The images of mounting the optics in the microscope, Assembly Instructions , might also help as the lens rendered there is 40×. If you have got a 35mm par-focal objective all is not lost, the wonders of 3D printing and CAD mean that you could make a new optics module to fit your lens.
