articles/Nature/extrememacro-page7

Extreme Macro - part 7 of 1 2 3 4 5 6 7

by Mike McNamee Published 01/10/2010

will be something like this:

PL 4/0.10 160/-

where PL stands for Planar (the flatness of the created image), 4 is the 4x magnification, the 0.10 value is the Numerical Aperture (a derivative of the more familiar f-stop), the 160 is the tube length and the /- tells us that the lens does not need a correction for a microscope cover glass. A lens intended for biological work might have a value, such as 0.17, after the back slash to indicate an optimum correction for an 0.17mm cover glass. Sometimes the word APO is added to the title which indicates that the lens is apochromatically corrected. If you are unfamiliar with microscopes you are better off taking advice and we found Brunel Microscopes to be most helpful and knowledgeable. The good news is that the 4x plan lens we purchased was £37.

This has a numerical aperture of 0.10, equivalent to an f-stop of around f4.5, a working distance of approximately 15mm and a field of view of 5.5mm x 3.0mm. The measured focal length is 40mm. It is not possible to successfully stop down a lens of this type (even if it had a diaphragm - some do) without introducing serious diffraction limitations and so people have resorted to stacking software. There are two main contenders, ZCombine and Helicon Focus and they have been used to spectacular effect. In use, you make a succession of shots incrementing the camera/lens combination forward fractions of a millimetre at a time.

• Extreme Macro page 1
  
• Extreme Macro page 2
  
• Extreme Macro page 3
  
• Extreme Macro page 4
  
• Extreme Macro page 5
  
• Extreme Macro page 6
  
• Extreme Macro page 7
  

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