The meaning of "magnification" in the virtual atlas

[giuseb]

I have been assuming that all virtual slides were acquired using either a 40x or a 60x objective, and that's what "magnification" in the Microscope Slide Information panel really means. Correct?

If so, experienced observers implicitly understand that the "40x" label indicates the magnifying power of the objective used for the digital scan, which has little to do with the actual magnification of the image on a computer screen.

On the other hand, I suspect that the term "magnification" may be confusing for many first-year medical students.

I would consider rewording, e.g. OBJECTIVE (or acquisition objective) instead of MAGNIFICATION in the Microscope Slide Information panel.

[giuseb]

I have also been assuming (again, please correct me if I am wrong) that slides were scanned only once, i.e. no 4x, 10x, or 20x objectives were actually used. If so, the actual meaning of the toolbar's "magnification" buttons is:

• the last one (usually 40x, in some cases 60x) sets the view at 100%, i.e. one image pixel per one screen pixel
• The other buttons zoom out proportionally by interpolating pixels, i.e. 4x = 10%, 10x = 25%, 20x = 50% of the above

During practice sessions, I often have to remind students that even though it says 40x, the actual magnification of the image on your screen is unrelated. On my 16" retina display, for example, it's more like 1000x, since the 50 µm scale bar is close to 50 mm wide.

Those 4-10-20-40 magic numbers do make sense as relative quantities to an experienced microscopist with an intuitive sense of how much magnification changes when switching objectives.

[ghost]

The maximum magnification shown in the toolbar (usually 40x with some 60x) is the magnification of the objective lens used to obtain the image. To clarify, MAGNIFICATION will be changed to OBJECTIVE in the Microscope Slide Information Panel. The slides were only scanned at the maximum objective magnification. The relationship between the objective lens and digital zooming works as you described. When viewing any digital photo, the inability to distinguish between physical lens magnification, digital magnification, display size, and pixel density is a big problem. This an intuitive skill we learn because we know the actual physical size of things being viewed (e.g., cat versus mountain). However, this must be learned again for small objects (microscopy) or large objects (astronomy). Magnification/zoom is usually displayed relative to 100% for one pixel in a photo matching one pixel of the display. We chose to display zoom relative to an objective lens to help students learn/judge the sizes of objects on a digital display. This made sense because students were also using physical microscopes in laboratories. Unfortunately, this is lost when students only use textbooks, atlases, or websites to view slides.