back

 

 

Complete suppression of ring artifacts in Coolpix cameras

H. O. Baral, Nov. 04

 

Summary:

Many owners of Coolpix cameras have observed artifacts (ring structures) in their pics when making micrographs at the light microscope through a 10x eyepiece, mainly when using 40x and 100x objectives. Especially Coolpix 4500 produces very strong artifacts (rosettes) when using a medium zoom position, but the strength of these artifacts obviously varies strongly among different series of 4500. With a 4500 which produces very strong artifacts, a method was found to completely avoid these artifacts, mainly by using the minimum zoom position. The following list summarizes the method for Coolpix 4500:

• set the zoom to its minimum (= maximum wide-angle) or very close to this. This means to use the shortest focal length (about 8 mm). When using the 100x objective the focal length must not exceed 9-10 mm!
• select highest resolution (4 Megapixel)
• set focus manually to macro (better than infinity!)
• set camera diaphragm to its full aperture (2.6; use A = aperture-priority mode)
• set microscope diaphragm somewhere above a medium position (test brightness on camera monitor)
• accept high vignetting and cut out the desired part of the image on the computer.
• make a series of pictures since the camera monitor does not allow to evaluate sharpness of small objects; a better control is achieved by using a TV-monitor connected to the camera by a video cable
• Position the camera as near as possible to the eyepiece
• the method allows free-hand fotos without any adapter, since the shutter-speed lies between 1/60 and 1/250 when using oil immersion (this is much shorter than with a medium zoom position)
  
  

With this method it is possible to completely avoid ring artifacts and resolve details of about 0.1-0.3 micrometers diam.

Please have a look at my detailed report (in German, with images).