This is a really clear and crisp explanation of why image quality can often be non-optimal in one sample, and completely non-standardised from sample to sample. Thank you! The partial solutions described are all good when considering the standard microscope slide system we have to work with. I would be very interested in talking to you about a way in which we can consider improving the sample position, during preparation, on the microscope slide rather than the partial solutions using the microscope.
Nice instructional video! Perhaps we can say that spherical shaped lenses are easier to manufacture and polish, and so they are used, but they are the wrong shape to focus to a point. This is why it's called spherical aberration. Large aspherical lenses are possible to make and are the right shape, but the tiny ones needed on objective lenses are super hard to make and so are not used, and so extra lenses in the objective are used to cancel out the spherical aberration from the spherical top lens.
