Focus Stacking: An Introduction

Belionota sumptuosa (Indonesia)

At left is a photo of a Belionota sumptuosa from Indonesia. Commonly known as a Tricolor Metallic Wood-boring Beetle.

It isn’t a regular photo, though. It is a focus stacked image.

Specifically, it is 276 photos combined to make a single image. When shooting macro, the depth of field — the distance in front of the lens that is in focus — tends to be really narrow. By taking a bunch of photos where each has a different depth in focus and then combining only the in focus areas from each image, one can effectively create a composite image that is entirely in focus.

So, this is really 276 images taken across about 40mm of camera travel; about 0.15mm of travel between each picture taken. I’ll cover that in a later post

Since optics are optics and physics are physics, changing the focal plane by either moving the camera ever so slightly (10 to 20 microns per photo, in this case) or by changing the focus depth via the lens’ focus ring, the scale of the subject changes just slightly and anything in the foreground becomes blurry and obscures the background.

All that has to be compensated for and there are a handful of software stacks that do exactly that. I’ll discuss those in a later post.

Belionota sumptuosa (Indonesia) Source Image

To put it into perspective, this is a single frame in the stack.

Only the tip of the feet and antenna are in focus. The focal plane is so shallow that not even the leg is in focus and the rest of the bug is entirely blurry.

On a lark, I put together a video of all of the frames in the stack followed by the final image. In 4K.

Fungus

There is nothing about focus stacking that requires a bit of computer controlled technology to move the camera multiple microns per image with crazy studio lighting (all of which will be discussed in later posts).

In fact, focus stacking really only relies that you can hold the camera still enough between multiple photos while also changing the focal plane, either by moving the camera or adjusting the focus ring.

For example, the image at left is a bit of gooey fungus growing in a fairly dark part of the forest. Normally, such a shot would require a lot of flash, a really tight aperture (high number– backwards), and as slow of shutter speed as possible. In a single shot, there would likely be some bright flash highlights, too.

In this case, I braced the camera on a log, cranked the aperture to relatively wide open so I could have a reasonably low noise (low ISO) image while still having a handheld compatible shutter speed and then shot 11 frames while varying the focus depth via the lens’ focus ring. I did use a flash, but I was able to turn down the intensity a lot, yielding fewer highlights.

So, yes, handheld focus stacking is possible. But hard. Add a cheap, small, tripod and it is no longer hard. Add a focus rail and the options expand. Etc until your wallet is empty, as usual.



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