articles/Macro/getting-very-close-page3

Getting very close - Part 3 - part 3 of 1 2 3 4

by Christopher Algar Published 25/01/2018

Paracetamol, 10x objective, stack of 29 frames.

For most of the subjects we photograph, the bright field illumination given by simply lighting the subject from below gives a rather 'washed out' effect. Our microscope has a swinging filter holder in which we can place a patch stop for dark field microscopy. The stop only allows light rays that have been intercepted by the specimen to reach the sensor,giving the dark background that we prefer.

Although we are using some of the same lenses on our microscope as we have for extreme macro with bellows, the technique and results are rather different. Whereas we use reflected lighting from above for our bellows system, our microscope provides lighting from below via an optical system. Positioning a specimen on our vertical stand is done by sliding the supporting tube about by hand but we have the much more accurate adjustable specimen holder on our microscope. One advantage of the bellows system is that adjustments can be made to the magnification by shortening the bellows length if a specimen is just too large to fit the camera sensor. In contrast, our microscope has a fixed tube which allows no adjustment in length. One way to overcome this shortcoming is to take two photographs and join them when editing. Doubling up on the number of stacked images is not a particularly attractive proposition but may be worth it if the image is good enough. An advantage of joining multiple photographs rather than taking a single stack at lower magnification is that more detail can be captured.

Citric acid, 4x objective, stack of 21 frames

When high-magnification lenses are used, the distance between the front element and the specimen can be so close that lighting from above is not practical. We have a 40x Nikon lens that we could not use on our bellows system due to the problems with lighting the specimen. There was also a problem with resolving the steps necessary for the short depth of field of this lens. When using our microscope, however, both problems are solved due to the lighting coming from below, and the resolution of the fine-focus control.

One of the condensers for our microscope has sideways movement which allows for oblique illumination. Lighting a subject in this way can increase the amount of detail captured and gives a different effect compared to using a ‘centred’ condenser.

• Getting very close - Part 3 page 1
  
• Getting very close - Part 3 page 2
  
• Getting very close - Part 3 page 3
  
• Getting very close - Part 3 page 4
  

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