Hi @ryantheengineer that is an interesting application. Could you post some pictures of your set-up?
I am not quite clear from your post whether you have now got the achromatic tube lens in the optics module. If you have not, then that is likely to be a big part of the issue.
If you have the tube lens in place then the most likely cause of your issue is the 4x lens. This has a very large field of view. The illumination on the OpenFlexure microscope is designed for high resolution 40x to 100x objectives. Those lenses need a very large angle of illumination to fill the NA of the lens, but only need a small illuminated area. It works well for 20x (or the low-cost optics which is equivalent to 20x), but at 10x it is difficult to illuminate the whole field of view with the focussed illumination. Of course it is possible to move the illumination back away from the sample to increase the illuminated area. This makes the angles of the light wrong at the sample and at the lens, which will degrade the resolution that you can obtain, however for a 4x lens this is less critical.
For a large field of view such as in your application there is another recent thread on different optics options, Refletion microscope without beam splitter.