I wondered if I give them proper testing, there might some pleasant surprise, at least with Zeiss 3.2x 0.10 Semiplan.
Fortunately, before every MTF testing I perform very simple and quick pretesting. It is actually start and end focusing point setting for my macro rail in order to align the sharpest focusing plane with MTF target. This is done by checking camera focus assistant that highlights object edges when in focus. The hysteresis of this system starts and ends when MTF resolution is at approximatelly 1000 LW/PH, which is fortunately a value of acceptably sharp picture. So every lens/objective that fails to show colored razor edge at any point does not qualify for further testing. This nice X-T2 feature have saved me many working hours and helped separating good from useless lenses (for photomacrography at least).
So during this preparation 3 out of 6 objectives failed to pass this basic test: Tiyoda 2x 0.10, Lomo 9x 0.20 and no name 4x 0.15. There was simply no need to spend any additional time for those three.
OTOH, next 3 objectives were showing clear colored edges in wide enough focusing range which is always a promissing scene to see. Those are: Zeiss 3.2x 0.10 Semiplan, Lomo 3.5x 0.10 and Lomo 3x 0.11. Actually, I had high hopes for Zeiss optics since that former Eastern Germany manufacturer was able to design some very fine objectives like recently tested 6.3x 0.16 Semiplan.
Close inspection has shown very simple and short design covered by external tube much longer than the optics itself. Removing it was logical move so I tested with and without it. All the objectives were tested at both nominal extension and shorter focused in quest for better performance.
Zeiss 3.2x 0.10 Semiplan ufortunatelly didn't justify it's big brother's fame showing just mediocre performance. Removing casing which is actually front aperture mask improved center resolution and CA but the edge resolution dropped even further. Shortening the extension tube by 30% improved both center and edge resolution considerably but for 1.9x magnification figures were still not something to write home about. And CA is still on the high side there. Removing the casing at this magnification does not improve center resolution by much but worsens the edge resolution to terrible figures.
Next came the objective performing much better than Zeiss 3.2x. Russian Lomo 3.5x 0.10 Plan is one very small finite objective with obviously simple design. Focusing plane is pretty straightened but far from flat. Resolution is pretty decent at both center and edges with exceptionally low CA. While shortening extension tube I was hoping for even better performance but that happened only with center resolution while the edge resolution and CA worsened a lot. To conclude, this is pretty fine objective available with budget price tag performing very good at nominal tube length.
Finally, there was #6 in this cheap objective survey which resembles older version of famous Lomo 3.7x.
With 16% lower magnification, Lomo 3x 0.11 produced 10% higher central resolution and 22% higher edge resolution than his 3.5x brother. CA was equally low which is wellcome bonus. And there is another "feature" that both objectives share: performance worsening when short focused by 30%. Central resolution jumps up but everything else gets worse so I don't recommend using it that way.
So, out of 6 cheap objectives two seem to be pretty good. In case you are on tight budget and want to dive into 3x magnification range, those two will not brake the bank while providing decent performance at default magnification. Don't expect extremely crisp and sharp stacks like those from Mitutoyo and other top notch objectives but those two might pleasantly surprise you!
