modernmicroscopy : columns : microscopy in the home shop


Constructing a Scanning Light Photomacrography System
by  Ted Clarke, Scientific Photographer and Instrument Maker

6/10/20061 | 2 | 3 | NEXT>> 

I was amazed by the scanning light photomacrography images Jim Gerakaris showed in his Inter/Micro-84 presentation a “Second Look at Scanning Light Photomacrography”. My own talk on “Method for Calculating Relative Apertures for Optimizing Diffraction- Limited Depth of Field in Photomacrography” complemented Jim’s talk by demonstrating the limitations of conventional photomacrography even with the aperture diaphragm stopped-down so much that the loss in image detail started to become visible.1   Jim’s talk was my first exposure to the apparently unlimited depth of field with the Dynaphot scanning light photomacrography system.2  My article on photography of fractured parts and fracture surfaces in Volume 12 of the ASM Handbook includes a description of the Dynaphot and comparison fractographs taken with and without scanning.3  This article also includes a table and graph based upon my optimum aperture analysis. The front cover of the Dynaphot sales brochure has a spectacular scanning light photomacrograph by Darwin Dale of the head of a fly, shown in Figure 1. The Dynaphot and its operating principles are well explained on the second page of the brochure, shown in Figures 2 & 3. There is some confusion caused by the brochure’s diagram in Figure 3, which claims that the specimen is scanned vertically through a thin sheet of light. The patent drawing by the inventor of the method, Dan McLachman Jr, clearly shows in Figure 4 that the beam of light from the slit lamps converges to a minimum thickness where it intersects the optical axis of the camera objective. 

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Figure 1
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Figure 2
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Figure 3
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Figure 4

 

The effect of the illuminating beam converging and diverging at the edges of the field being recorded and the diffraction limited minimum beam thickness at the center of the field was the subject for my later publication of a mathematical analysis of the scanning method including a photograph and description of a scanning illumination system of my own design to be used on my very robust and precise photomacrography stand.4  This stand is intended for use in photographing parts and fracture surfaces of significant weight and is based upon restored components of an early twentieth century bench-lathe. The stand with the completed scanning light system is shown in Figure 5. A microscope eyepiece adapter with a 10X high eyepoint eyepiece is shown mounted in place of a parfocal Olympus 35 mm camera back. This eyepiece adapter was initially intended as an aid in viewing the fine details and as a relay lens for an eyepiece-mounted Nikon Coolpix 995 digital camera to be used for test exposures prior to final recording on film. I was pleasantly surprised to find that the test exposures with the digital camera were of high quality, even with the shutter held open on B (bulb) setting for 12 second scans. Figure 6 is a scanning light photomacrograph of the head of a house fly taken with this now completed system. The 35 mm film camera would record a much larger field area at somewhat higher resolution than the digital camera.

 

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Figure 5
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Figure 6

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