Last time, in Figure 13, we saw a series of four pieces of pyrite with increasingly numerous individual crystals within the same approximate volume of material. Figure 14 shows the two finer grain rocks, with insets of Figure 13's Crystal B at the bottom and top of the photo. The lower inset shows the true relative size of the individual crystals of Crystal B to the others. But the upper inset has been resized, and the crystals look just a bit larger than some of the largest individual crystals to its left. So, again, it can’t be overemphasized that you must know the magnification of what you are looking at. With our everyday lives, this is automatic. When we get to the small world of microscopy, we can’t run on automatic. We have to think and investigate or at least ask questions.
Figure 15 shows two higher-magnification views of a largely overlapping area of our original Pyrite B. Some people might say “closer views.” If we want greater magnification with nothing but eyeballs, we have to go closer to the object. In general, magnifying lenses also get closer when the magnification goes up. Want a high-magnification optical zoom lens on your camera, say a 5x? You will be VERY CLOSE to your subject. This is a bit of a pain because it doesn’t make it easy to move the thing you are taking the photo of very easily. Want a longer focal distance? Now that gets really expensive. The new technology of zoom features on digital cameras turns a lot of these problems into smaller annoyances.
Now back to Figure 15. Note the smaller, differently shaped dark crystals at location B. These are in Figure 13, but essentially invisible at the light exposure and angle used to capture the image. See if you can find the area of the dark crystals now in Figure 13. This will train your eye to recognize crystalline shapes, useful for interpretation of any microstructure. Note also that the red specks within the dark crystals show up much better in the brighter exposure at the left. The brighter exposure also shows the step features at locations A and C. But the small faint steps at locations D and E are almost invisible at left and easily visible in the darker exposure. It can’t be overemphasized that it is usually going to be impossible to show everything that might be of interest in a single image. Specific angles, light exposure and limitations of depth of focal field are all contributors to that reality.
More next time.