Tuesday, March 23, 2010

Looking closely at CDs

I've always been intrigued by the dividing line between the written and unwritten areas on a CD-R. All CD-R formats begin writing in a spiral track starting at the inner radius of the disc and proceeds to the outer radius, so the inner area is written data, while the outer area is still blank. The inner area usually looks lighter in color.

I first placed the CD-R on the microscope stage, bottom-up. This worked at "medium power" 10x, but I could not focus at 40x because the thickness of the CD itself did not permit focusing the 40x objective. Instead, I scratched off a little of the protective coating on the CD top surface, then inspected it from the top.

This is a very old Memorex CD-R. Green-blue dye with a gold top-layer. I lit the CD-R from below with the microscope's built-in light. The image was pretty dark, but by setting the camera exposure to 3 sec, the final image looks great.

Here's a shot of the dividing line between the data area (upper half) of the disk and the blank unused portion of the disc (lower half). The length scale is approximate.

Here is a %100 crop from my camera. The length scale is approximate and computed by dividing the frame height of my camera (13mm) by the microscope objective's magnification (40x), then scaling in GIMP to make the bar an appropriate size for the crop. I checked Wikipedia, and it appears the track spacing for a CD-ROM is 1.6um, so I wasn't too far off.

Sunday, March 21, 2010

Photomicography (microphotography) with Lumix GH1

I bought a 2x achromatic objective for the microscope and also discovered that positioning the camera closer to the objective by removing microscope parts will increase the field of view (lower magnification). This is very useful since the 4x and even the 2x objective have too much magnification for large insects and similarly-sized objects.

I added photos of a large orb-weaver spider.

Since buying a Lumix GH1, I have been excited to attach it to my telescope, microscope, and any other imaging device so that I can capture unusual photographs. Today, I got all of the parts together and tested it with a microscope for the first time.

The microscope is a Labo VJ-71. It's a decent-quality student microscope with DIN 4x, 10x, and 40x objectives. I also have a remote shutter release for the camera, an LED on a flexible mount for top-lighting, and eyepiece (not needed for photography)

In order to attach the camera to the microscope, I found this microscope->Nikon adapter that I had built years ago. The barrel fits inside the microscope tube and provides a Nikon lens mount. I got the lens mount from a very old, very broken lens. I have a m4/3->Nikon adapter, so I can attach this to the GH1.

The first problem that I noticed was a bright, fuzzy spot in the middle of the image. I removed the camera, and looked down the microscope with all of the adapters in place, but no eyepiece. I could see a lot of light reflecting off the tube's inner walls and this ring of light was landing on the sensor and ruining the image. I added a washer to the Nikon adapter to act as a baffle. This helped, but I also ended up unscrewing the eyepiece tube from the microscope, and inserting the Nikon adapter into the microscope body. This shortened the distance between the camera and the objective, so there was less tube wall to cause unwanted reflections.
I started with this dandelion flower. This image is shot with my Vivitar 28-90, at 28mm

Here is a photo taken directly from the microscope. The objective is only 4x, but as you can see, the overall image is highly magnified. This cluster of pollen parts on the flower is only a few mm in width.

Another problem with microphotography is the extremely shallow depth of field. Even with the 4x objective, there is not much in focus. A neat solution to this problem is to use photo-stacking software, and stack a whole bunch of images taken at different focal depths.
I used CombineZM, a free software tool to do the alignment and stacking:


The head of a common house fly. Yikes!