More Focus Stacking

This little fellow is a hatchling turtle carved from Phytelephas “nut”, which looks a great deal like ivory. Detail I want to capture includes the small spots on the inside of the egg shell (behind the turtle). He’s a trick to photograph because all three of his dimensions are about equal in extent. That means he takes a big depth of field to shoot if you are going to fill the frame. I put my macro lens on, and the best I can do is the next shot, which was taken just to show the scale of the turtle.

The shot with the coin was taken at f/22, in crummy light; the exposure was about 2.5 seconds at ISO 200. The depth of field is still not as large as I want, and in the original there is substantial blur—which is probably diffraction. The focus stacking result is much, much more pleasing. I used the brilliant combineZM software (free as in GPL) to assemble about 20 shots into the main picture. A sample of those shots is shown below. You can see the position change, which was due to my unstable platform. combineZM is doing an amazing job of aligning the images.

As you can see from the focus range on frame 9, I provided too frames for the first half of this set. I probably should have shot close to 40 images. I also think it would be worthwhile to be very careful in moving the inter-frame focal point. Finally, the defocus on the near components of frame 20 looks bad—it looks extremely non-Gaussian, and I suspect that is responsible for some of the artifacts I had to work hard to suppress. I hope to get my hands on a Nikkor AF-S 105 mm f/2.8 micro relatively soon, perhaps that will help…

With respect to reducing artifacts, the leader shot is actually a composite of two products from combineZM. Overall, the best shot came from the “Do Stack” macro; however, the edge of the shell directly above the turtle was blurry (circled below). The “Soft Stack” macro produced a crisp shell above the turtle; however there were odd looking artifacts (inset) all over the image. The final result I got by masking in just the sharp parts of the shell from the “Soft Stack” macro while leaving almost all of the image as the result of the “Do Stack” macro.


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