Focus Stacking

I have been into macro photography lately, taking fun photos of things I have around the house, like salt and snapdragons, and occasionally venturing farther afield to find some flowers. Here are two of my latest.

Pro Tip: Click on the pictures in this blog post and view them large, on a computer screen. They will look much better on a big screen than on a phone.

One of the factors which makes these photos visually compelling is that the entire subject is in razor sharp focus. Here are a couple of 100% crops from those two shots, which means that you are seeing them on your screen with all of the detail from the photo.

Every detail is crystal clear, from the top of the giant piece of Himalayan salt to the bottoms of the tiny pieces of sea salt even though the top of the Himalayan salt “boulder” is much closer to the camera than the little pieces of sea salt.

You can clearly see individual fibers in the sea bunny’s ear (left) and tail (right), even though they are pretty far apart. Photos like these look special because we do not get to see photos like this very often.

If you try to take a close-up picture, you usually get some parts in-focus and others slightly blurry. Here is an example.

The prickly rose bud is in-focus. A few of the thorns are in-focus but most are out of focus. It works for this photo because it directs your attention to the rose bud and, well, we are just used to seeing pictures like this so we don’t give it a second thought.

If you know a little bit about photography and want more of the picture to be in focus, you might ask, why not just stop the lens down to a smaller aperture, like f/16 or even f/32? It turns out that, although you get more depth of field at smaller apertures, the image loses sharpness. If you want to know more about lens diffraction in photography, jump over to What is Lens Diffraction? at PhotographyLife. That article starts with a great illustration of the effects of diffraction at six apertures, from f/5.6 to f/32.

In addition to sacrificing sharpness, an image with greater depth of field does not mean that more of the image is in-focus. It still has just a tiny portion which is perfectly focused; it just has more parts which are only slightly blurry instead of very blurry.

So how do we get a photo with everything tack sharp? Computers to the rescue! We take a whole stack of photographs, each with a tiny portion of the picture in-focus. The computer then takes the best part of each picture in the stack and combines them into one image.

I shot a stack of 100 photographs of the sea bunny (felted by the very creative Nicole Mann). My Nikon Z 5 camera does the heavy lifting with its Focus Shift feature. I set the camera to take 100 pictures, automagically adjusting the focus very slightly between each shot. A tripod helps, too, of course.

Here are two of them, just as they came out of the camera. In this first photo, you can see that the seashell in front of the bunny is in focus and the bunny’s nose is almost in focus. Everything else is blurry.

Here is a photo from the middle of the stack. You can see that there is a strip in the middle of the bunny that is in focus but both the ears and the tail are blurry.

I use Zerene Stacker to process the individual photos into a focus-stacked image. Here is a little screen capture video of Zerene running. As it runs, each of the individual photos appears in the left pane while the processed image gets clearer and clearer in the right pane. (As you watch the video, you will see some variation in brightness. I shot this near a window using sunlight and a couple of clouds drifted past the sun while the camera was taking the pictures.)

In addition to building the focus-stacked image, I did a little bit of retouching in Zerene. There were a few strands of fiber which did not get rendered quite right. Zerene makes it easy to manually find the image in the stack which has just that strand sharp and then copy just that part of the picture into the final image. I did that in a few places.

I saved the resulting image as a TIF file so that I could open and edit it again without losing any quality. JPEG images are “lossy” which means that every time you open, edit, and save them, they get a little blurrier.

I did a little more editing of the TIF file with RawTherapee. I tweaked the white balance, removing the greenish tint that the window glass had created. I used the Tone Mapping tool to make the colors more vibrant, the brights brighter, and the darks darker. Finally, I cropped the picture and resized it to exactly fit a 4K computer monitor. (Remember the pro tip from the beginning of this post? That’s why I wrote what I did. I carefully crafted the image to look best on a computer screen.)

My Macro Photography gallery has more of my pictures.