When we use a usual biology class compound microscope, we need to focus the stage (place the object) to the "correct" position. It is just in that sweet spot that the image is sharp and clear. So we are deciding the object distance.
Here is the ray diagram of a compound microscope.
So, when we are focussing, we move the objective lens which tweaks the image distance. My doubt is that, shouldn't the image be seen clearly, wheresoever the first real image forms, if within Fe (Focus of the eyepiece lens). Then, that would make it a range instead of a single point (shouldn't we be able to see a clear image not at a single point but a range?). Whatever, the distance of the virtual image, the eye can accommodate it onto the retina, right?
If the first image (real image of the objective lens) goes behind Fe, or is on Fe, what happens?