focus stacked images

[mikehrabar]

Three image composites. The closeup of a wasp face is a Polistes aurifer male, the wasp abdomen is a similar species (Polistes fuscatus), female, with a parasitoid poking out (Strepsiptera). The bedbugs feeding, is a handheld stack of only 5 photos.

See video showing a bedbug expanding as it feeds in the video forum. You can see the gut move as it is pumping blood!



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[deliasfanatic]

Hi Mike - welcome to the forum! What stacking software do you use?

[wollastoni]

Very impressive !

[jensb]

A question i have how do you make sure you have no parts between the stacked images that show
a very tiny part that isn't sharp. That is a problem i always have.

Greets jens

[mikehrabar]

Zerene software was used for these images.

jensb, I think what you are referring to is the haloing that occurs around things that extend into the foreground, like insect antennae. What causes the halo is that the part of the background covered by the antenna differs when the antenna is in focus and when it is out of focus. basically, as the camera moves in, the antennae shifts to the periphery of the field of view (parallax). The closer the camera is to the object relative to the height of the antenna, the more pronounced the smearing.

I have Found that some smearing can be a good thing, helping to delineate the foreground structures (if everything is in focus, the image will appear rather flat). One way to mitigate the effect is to stop down a bit (or use a lower power objective), to increase the depth of field (at the sacrifice of some resolution).

Also, The Pyramidal algorithm (Pmax in Zerene). Has the property of maximizing the sharp parts, and minimizing the halo. The problem with Pmax is that the antennae will appear somewhat translucent, showing some background through it. I then go through the retouch feature, and select the antennae in the frames where it is sharp. This is the only way I have found to get the extremely sharp images, while minimizing the halos.

[mikehrabar]

Oh, in reply to jensb, another consideration to reduce haloing in the high magnification stacks, is subject positioning! Always an important consideration. Placing the subject in such a way that things like antennae won't interfere with important background parts is important.

The final one that I can think of is lighting. In the extremely high res stacks, one must resort to very diffuse light. The parallax issue is exacerbated by shadows. I use a ping pong ball, cut open at both ends (or cut into a dome shape, to create a spherical diffuser. It allows for very uniform lighting.