First image is a focus merge of my new AmScope 4x Plan Finite microscope objective with 36mm of extension tube followed by a 2x teleconverter which yields more than 4x, but probably only around 4.6 to 5x.
These next ones are a bunch of test images. I just got the objective yesterday and this is my first time ever using one. My experiments show that beyond 4x lifesize magnification, a microscope Plan objective is indeed sharper than a purpose built macro lens and costs magnitudes less. One thing I didn't know is that the Finite 4x Plan objective I got from AmScope can be used for more than just 4x lifesize work. It's dependant on how far away the objective is from the body. With no extension tubes is basically 1:1, and as you add more the more magnification you get. I wasn't expecting this, I thought it'd only come to focus at a very set distance from the camera and offer only 4x magnification so it is more versatile than I thought. between 1-3x lifesize, the macro and the microscope objective are fairly equal in terms of sharpness, although I am leaning towards the microscope objective.
Here are the tests:
Frost:
Ruler: