articles/Nature/extrememacro-page6

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

by Mike McNamee Published 01/10/2010

Many lenses will perform better if they are reversed. This is logical if you think about it. When working normally a lens has a nominal rear working distance equal to its focal length (ie 50mm for a 50mm lens set at infinity). If it is reversed, then used with the subject a short distance away, it is working close to its optimised parameters - light does not care which way it is passing through a lens! There are a number of other technical considerations which change the working distance from the nominal 50mm; for instance at 1:1 magnification the working distance will be 100mm both sides of the optic.

This is a reason why you might not see the benefits of reversing a lens until it is used at greater than 1:1. Many adaptors are available for both reversing and re-introducing aperture auto-shut-down of lenses. The Nikon PB-6 bellows may have its front standard reversed for example and the double cable release will still operate the aperture close-down. As with all things digital, complex exposure calculations are no longer needed; you find the exposure by trial and error using the camera histogram.

Using Microscope Objectives

Providing you can cope without aperture control, the humble microscope objective lens makes an excellent high-power macro lens. Normally a microscope objective lens is corrected with the intention of creating an aerial image 160mm (or sometimes 210mm) back from the lens. This is known as the tube length. The image that is created at this distance is magnified by the stated value on the barrel.

In the compound microscope the eye-piece further magnifies the image and often corrects any residual optical aberrations. Microscope objective lenses are reasonably standardised including the nomenclature on the barrel which

• 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
  

There are 37 days to get ready for The Societies of Photographers Convention and Trade Show at The Novotel London West, Hammersmith ...
which starts on Wednesday 17th January 2024