Focus Stacking multi-shot technique

General description

Focus stacking is a multi-shot technique that creates single images with an extended range of focus from a collection of images with more shallow focus. The technique can be applied to any scene, but it finds greatest application with high magnification setups because the optical depth of focus in those applications is very narrow.



For large scenes, the source images can be acquired by focusing on just a few different points. With more flexible equipment, the Scheimpflug technique can be used to reduce the total number of required images.



Small objects will requre many source frames produced my moving the camera between exposures (13 for the micrometer).






Really small objects will requre many source frames produced my moving the camera between exposures.
Refocusing is not practical at high magnifications because of the attendant changes in image size.



Subjects up to about 5" can be photographed by manually adjusting a focus rail.
The pictured unit is the B150-B from RRS and provides 1mm of camera movement per revolution of the drive screw.



For really small objects like insects and small parts, you pretty much need an automated camera transport.
The pictured StackShot automates image acquisition and camera movement.



The Sharpie Project

How sharp is the Sharpie?



Everyone has used a Sharpie, but we often don't get a real good look at the business end of this ubiquitous product.



We can examine details of the Sharpie tip by creating a multi-focus image stack.
The Leica DMS1000 digital microscope is shown above along with camera settings and stack definition for 20 images.




After executing a stack acquisition process for the Sharpie, we have 12 source images, one depth map and and the resulting montage.




The depth map on the left is like a mask that correlates each frame in the stack to its corresponding Z-axis acquisition elevation. The resulting montage shows all parts of the tip in sharp focus. For the first time you can see that it appears to be made of at least two different fiber types.





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