I chose as a subject some Chlorargyrite with Cerussite from the San Rafael Mine in Nevada, collected in September of 2010.
To take the photos I am using my Canon 20D DSLR camera, along with the Canon MP/E 65mm macro lens. The camera and lens are mounted on a very sturdy Manfrotto (Bogen) 3046 tripod pointed straight down at the specimen, which is sitting on my desktop. The Chlorargyrite bleb is quite small, only visible with difficulty by naked eye.
The first image gives an idea of the scale I am working at. It is a photograph of a portion of the scale on a Starrett caliper. The numbered major divisions are 0.10 inches apart, so the small division are 0.025 inches. The MP/E lens is set to about 3.5x to get this image size (the MP/E allows from 1:1 to 5:1 magnification). The 20D camera uses an APS-C sensor with a 1.6 crop factor which actually is beneficial in this application, giving some additional magnification.
The field being photographed is 0.25 inches, and with the lens set to approximately 3.5x, this will yield an image 0.875 inches wide. 0.875 inches is 22.2 mm, which is exactly the width of the APS-C sensor (which is 22.2 by 14.8 millimeters). It is nice to know that all this checks out.
For the purposes of these tests I am capturing images in medium size JPEG files (letting the camera produce the JPEG images) which are 2544 by 1696 pixel, then these are reduced to 480x320 for the web as you see here. Ultimately I will let the camera capture raw files in full resolution (3520x2344).
The four photos below (field is 0.25 inches left to right) were taken as follows:
Although I have the white balance settings right for the last three photos above, they look a bit magenta to me (not to mention underexposed). This can be fixed with Camera Raw and/or Photoshop, but I'll have to start doing raw captures and get out the big hammer (Photoshop).
Coming soon: cropped sections from the above images for comparison.
Exposures taken at 1/250 and f/16 without the flash would be essentially blank black fields. My intention is to suppress all ambient light and get all the illumination from the flash at a significantly shorter exposure time. The photos taken with electronic flash are clearly sharper, but still not as sharp as I would like. I will have to build a very sturdy stand to get any more reduction in camera vibration, and I intend to do so. I don't believe I am at the limit of what this lens can do. Having a stand to hold the flash would be preferable to holding it in my hand and using the off camera ETTL cord as I am currently doing.
A commonly cited drawback to using electronic flash is the inability to have a "modeling light" to orient crystals to obtain partial reflections from selected faces. I'll have to work with this and see how much of a limitation this is. I also intend to experiment with homemade flash diffusers and fill reflectors. Right now I am just probing to see what I can accomplish with the equipment I have in hand.
I also need to try taking photos through my Nikon SMZ-10 microscope. Even though the eyepieces are somewhat out of alignment, this would not affect the trinocular tube used for photography.
Tom's Mineralogy Info / firstname.lastname@example.org