I recently tried a rented sony nex-7 with a 2.5x connector (the last was a disappointment) and got a couple of interesting shots.
Here's an ostracod with 5x planachro and the cursed 2.5x connector, single shot (HDR - camera's sensor gets good dynamic range in raws), + minor sharpening and levels adjustment. Polarized light.
Overall, I am disappointed with the fact that the sensor out-resolves the image. In the future I'll keep using 0.75x connector for still images. But the videos made with this setup are stunning! I hope to show them in the nearest future.
Visit http://notes-from-dreamworlds.blogspot. ... light.html if you want to see a couple of other shots. They are just less spectacular than this.
Images made through a microscope. All subject types.