“Compound microscopes with a twist–these have special lighting systems that sends the light down through the objective and reflects back up through the objective, letting you see high magnification values on opaque objects. Commonly used for fault inspection, coating thickness inspection, silicon wafer inspection, and other “metalline” sample viewing.”
What does a metallurgical microscope do that a brightfield compound microscope can’t?
A metallurgical is essentially a high power compound microscope that can view opaque objects. Light does not need to pass through the sample on a metallurgical microscope in order to be visible, as they do not use traditional transmitted light that comes from the bottom. They gather the light reflected off of the sample (which means the light is coming from the top, where the objectives and eyepieces are).
How does a metallurgical microscope view opaque objects?
A metallurgical microscope uses a special illuminator and objective setup called “EPI illumination,” or reflected light. This light travels from a box attached between the head and the objective turret of the microscope, and is reflected down the objective by a mirror. It comes through a specialized objective, which is able to allow light to travel down through the objective, and still allow the light reflected off of the sample up into the objective, prism, and eventually visible in the eyepieces.
How does the reflective light illumination system work?
The light originates from the illumination box, then travels to a piece of glass coated with a reflecting element. The light coming from that angle is reflected down into the objective, and focused on the sample. Light is then reflected back from the sample up into the objective, and then travels at a different angle on the reflecting element, which allows it to pass through the glass instead of reflect off of it. It then reaches the eyepieces, and is visible to the human eye.
You can expect to see an image similar to this when using a metallic sample under this kind of microscope, but since it can view any opaque object, there are a number of non-metallic applications for it as well.
I’ve read that you can get into even more specialized kinds of metallurgical microscopes–darkfield and polarizing to be specific. What do those microscopy methods offer?
It gets a bit more technical when we get into this, but more specialized kinds of metallurgical microscopes basically do exactly what it sounds like–they are used for more specialized applications. I’m not typically of the school of thought where I believe if you need something so advanced, then you probably already know what you’re doing. That’s simply not true and a huge generalization! So we avoid that here.
A darkfield metallurgical microscope is primarily meant for viewing tiny fractures in a metallic sample. The darkfield element here is in the objective head though, not a condenser like a traditional transmitted light microscope. So the bending of the light comes from above, which is expected when you have a microscope that only has light coming from above.
A polarized light metallurgical microscope deals with viewing metallic alloys and compounds that ultimately are made up of various minerals. Polarized light is light passed through a polarized lens and an analyzer to direct the filtered light at specific angles and directions to the sample. When the light hits the minerals, they reflect with a variety of colors, based on what the mineral is and the angle that is being used with the analyzer. So it can be used for a great variety of real world applications where mineral identification is critical.
Can you help recommend any basic metallurgical microscopes? I’m new to this and afraid of buying the wrong thing!
Certainly! If you need a basic brightfield metallurgical microscope, I would recommend something like this AmScope ME300TZ-3M (includes MU300 USB2.0 camera for digital imagery).
For more specific information or additional reviews on this microscope, feel free to click the image above, or here: ME300TZ-3M