Introduction

Focus stacking photography or Extended focus imaging is a technique used when picturing small objects of specimens which are difficult to get sharp completely at the best parameters of both the lens and the camera. Usually it is possible to step the aperture of the lens down by using a large F-number and adding a lot of light. However this will result in a lower quality image because of the reduction of the optical resolution due to the diffraction effect. To overcome this problem it is possible to take multiple pictures each at different distances of the specimen with an overlapping field of view to create a complete sharp image.

In the RBINS we have put together a setup using Canon cameras and lenses, which are displaced and controlled by a Cognisys Stackshot. Depending on the size of the object photographed another lens can be used. The lens we use the most is the Canon MP-E 65 mm which can magnify an object 5X on the sensor of the camera.

The technique is daily used in the Scientific Heritage Service and setups are operated in almost every department. It is typically used for specimens ranging from 2 mm up to 20 cm.

It takes some time to complete a set of pictures for a single view, therefore the technique is only used for digitization of types (the first specimens used to describe a species) and published specimens. Regularly a request for pictures of specimens or a loan of the physical specimens is send to one of the curators. By taking pictures of these requested specimens, a loan of the specimens is often avoided.