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Steve writes:

This is a rather unique MPOD that won’t be of interest to everyone, but for those that enjoy thin sections and especially folks that want to dabble in thin section photography themselves without investing a lot of money, I hope you’ll find it entertaining and possibly even helpful in putting together your own photographic petrology setup.

A digital inspection microscope provides an easy way to get started with thin section photography. Photo 1 shows a simple, yet effective setup that’s easy to replicate. This example employs an Andonstar model ADSM302 microscope (usually around $300 or so, though I’ve seen it as low as $215 recently), but there are several less and more expensive options available depending on the image resolution and screen size one prefers.

The ADSM302 comes with a wireless remote, offers variable magnification (advertised up to 560X, but take that with a grain of salt), captures reasonable photos up to 12 MP with its CCD sensor, supports 1080P videos, and accepts a microSD card for storage. It can also be connected to any HDMI TV or LCD projector for presentation use, and it has LED goosenecks that allow reflected light illumination for imaging pieces of meteorites, or for simultaneously lighting opaque materials in thin sections (like metal) – something I remember seeing Tom Phillips do more than a decade ago to add additional detail to many thin section images.

One advantage of the ADSM302 is that it’s been around for a while, so there are some relevant accessories available: a $30 macro lens and a $15 polarizing filter for the objective (though this and additional filters for the gooseneck lights can also be fashioned yourself from the polarizing filter lenses in $3 3D theater glasses). By rotating the protective objective lens cover with the polarizing filter inserted, one can find extinction (the point where the pure glass part of the thin section appears black), and then if one is only interested in structure or art, it can continue to be rotated to vary the colors of the different thin section’s minerals (but to use the Michel-Levy charts for mineral identification, the actual slide must be rotated instead).

For the transmitted light source that the thin section slide sets on, I created something simple with a high-intensity white LED, a 5v USB phone charger, and a simple $5 dimmer circuit – all mounted in a small plastic hobby box. Under the hole for passing the light, I attached the lens from a pair of 3D theater glasses and a piece of semi-translucent plastic available at craft stores to diffuse the light. But those in the U.S. could just as easily purchase one of the $2 blue LED flashlights at Harbor Freight and put the polarizing film and light diffusing plastic on top of that to set the thin section onto (it’s not important to be able to dim the light, as the microscope automatically adjusts for light intensity and has additional manual exposure compensation as well).

The results are surprisingly good: you can see an example of a Wells chondrite meteorite thin section on the display in Photo 1. White light photography is also possible by removing the polarizing filter (obviously most easily done with the LED flashlight illuminator), which can show details and structure that often can be hidden in xpol images (especially at certain rotations).

To show what’s possible with this kind of setup, I took images of several different thin sections (the process took about an hour, with some additional cropping afterwards for pairing onto the photos). These were taken at various magnifications that ranged from minimum to maximum zoom depending on what details in the thin sections I was interested in capturing. For comparison, I’ve included links to any corresponding full gigapixel scans of these thin sections created with a much more expensive automated system I cobbled together (Photo 2); however, please note that the mineral colors will likely be different, as might be the alignment between the MPOD and gigapixel photos.

Photo 3: examples of various kinds of chondrules in ordinary chondrite meteorites:

NWA 11188 LL3 Chondrite Thin Section (gigapan.com)

SaU 001 L5 Chondrite Thin Section (gigapan.com)

SaU 001 L5 Chondrite Meteorite Thin Section (white light) (gigapan.com)

Photo 4: historic ordinary chondrite meteorites (Siena and L’Aigle):

Siena LL5 Chondrite Meteorite Thin Section (gigapan.com)

Siena LL5 Chondrite Meteorite Thin Section (white light) (gigapan.com)

L'Aigle L6 Chondrite Meteorite Xpol Thin Section (gigapan.com)

L'Aigle L6 Chondrite Meteorite White Light Thin Section (gigapan.com)

Photo 5: carbonaceous chondrite examples:

Allende CV3 Carbonaceous Chondrite Meteorite Thin Section (slide 3, xpol) (gigapan.com)

Allende CV3 Carbonaceous Chondrite Meteorite Thin Section (slide 3, white light) (gigapan.com)

NWA 3118 CV3 Carbonaceous Chondrite Meteorite Xpol Thin Section Image (slide 1) (gigapan.com)

NWA 3118 CV3 Carbonaceous Chondrite Meteorite White Light Thin Section Image (slide 1) (gigapan.com)

Photo 6: HED class eucrite examples:

Tirhert Eucrite Meteorite Thin Section (final) (gigapan.com)

Aounet Lagraa Unbrecciated Eucrite Meteorite Thin Section (Xpol) (gigapan.com)

Aounet Lagraa Unbrecciated Eucrite Meteorite Thin Section (white light) (gigapan.com)

Photo 7: HED class diogenite and howardite examples:

NWA 6695 Howardite Meteorite Thin Section (gigapan.com)

Photo 8: ungrouped achondrite meteorite examples:

Erg Chech 002 Achondrite Meteorite Thin Section (Xpol) (gigapan.com)

Erg Chech 002 Achondrite Meteorite Thin Section (white light) (gigapan.com)

Photo 9: Martian planetary meteorite examples:

Zagami Martian Shergottite Xpol Thin Section (gigapan.com)

NWA 10153 Martian Nakhlite (gigapan.com)

For those new to Gigapan, click on the diagonal arrows at the upper left of the image to go into full screen mode, then use your mouse to pan around and its scroll wheel to zoom in and out.

Although the Andonstar images can’t approach the magnification of the more expensive system’s gigapixel images, it does have an advantage over conventional petrology microscopes; like the mosaicked gigapixel images when zoomed out, the Andonstar’s wider field of view at its lowest magnification allows one to see macro details not easily visualized at even the lowest powers of traditional optical microscopes.

Especially for the money, this relatively inexpensive digital inspection microscope approach to exploring thin sections offers a great way for anyone to get started, and for the educator, it provides a capable, yet easily portable device for lectures and/or real-time demonstrations.

If there is interest, I can also do a similar MPOD on how to do gigapixel imaging of full thin sections.

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