Photomicroscopy with a NX1000

One of the things I had hoped to do with the NX1000 and the NX3000 I acquired earlier this year was to mount them to an Olympus BH-2 research-grade petrographic (polarizing) microscope I have access to. I had used an OM-2s film camera on this microscope for a couple of decades to photograph thin sections of rock samples in transmitted light, but that use faded as my needs changed and as film became less convenient and economical to process. Also a factor was that respectable quality DSLRs suited to the task remained at price levels too high for me to justify for occasional use. Oh how things have changed. What one can do with a few hundred bucks these days.

I fitted an OM-NX adapter to these inexpensive NX cameras, which enabled me to mount them onto the photo-ocular tube on the Olympus microscope. There is no camera glass in this setup, just the body and the microscope optics, which are very high quality objective and photo-ocular lenses. The camera’s job is just to meter the exposure in AP mode (varies from tenths of seconds to seconds with ISO fixed to 200) and capture the image on the sensor; focusing is done manually on the microscope. I utilized the 8x mag on the focus assist function, which worked better than the superfine matte focusing screen designed for photomicroscopy that I had mounted in the OM-2s in the film days. Generally, focusing on petrographic microscope slides is pretty critical. Even though the rock slices are only 30 microns thick and largely transparent, the depth of field is so shallow that it is possible to focus up and down through the thickness of the slide.

I first tried the NX3000, primarily because its flip-up screen makes it very comfortable to compose the image (the camera back faces straight up when mounted on the microscope), but I quickly discovered that my Samsung remote shutter release does not work on the NX3000. The exposures I took without it lacked desirable sharpness, but the NX1000 stood ably in its stead, with the shutter release preventing vibration from degrading the longish exposures.

Shown below are two of the images I captured today. They are of a grain of the mineral orthopyroxene from a rock from the Charlevoix region of southern Quebec. This grain displays spectacular kink bands — deformation features that crinkled the originally perfectly planar lamellae seen in the image. The colors in the image (just greys in this particular case) are due to an interference phenomena that occurs when a birefringent mineral (a mineral whose refractive index varies with light-vibration direction) such as orthopyroxene is observed in cross-polarized light (two linear polarizers, one placed above and one below the thin section, arranged with their vibration directions orthogonal to each other); birefringent minerals have the ability to rotate the plane of polarized light, hence can pass light through crossed polarizers.

The scale of the images is somewhat less than 1 cm across. Both images are processed from Raw using Adobe DNG Converter, and then lightly touched up for tone and contrast in Adobe PS CS6; no sharpening was applied. I hope the images have a pleasing aspect, even without a more detailed and technical explanation of what is going in this usually hidden, micro part of our world.

A close examination of the images at full screen, or even more so at 100%, shows a some softness overall, which is most probably attributable to the very shallow depth of field in a photomicroscopy mentioned above. However, there is a more noticeable softness on the left sides. I suspect this it due to one of two possibilities: a slight decentering of the objective and ocular lenses on the microscope (I have not checked their alignment in a few years, and now I have it on my list), or imperfect tolerances on the parallelism of the flanges on the OM-NX adapter I am using (a $10 ebay special), given that really shallow depth of field in photomicroscopy mentioned above.

Orthopyroxene with kink bands 1

Orthopyroxene with kink bands 2