It's focus stacking so basically just compensating for the way macro lenses and large apertures work. There's nothing artificial about it, the software is just layering the sharpest parts into the photo. It's a common technique, heavily used for things like astro photography and landscape photography as well. https://www.canon.co.uk/get-inspired/tips-and-techniques/foc...

Optical reasons, aka depth of field. Exceptionally well explained in

Cameras and Lenses – Bartosz Ciechanowski https://ciechanow.ski/cameras-and-lenses/

Depth of field - Wikipedia https://en.wikipedia.org/wiki/Depth_of_field

> My, that was a yummy slime mold!

This is a NetHack reference for anyone unfamiliar.

>Is this a workaround to let us see “what it would look like”, or are there optical reasons why this produces an image that is inherently artificial, and could never really be perceived that way?

Both in a way. When you look at a landscape, your eyes and brain are constantly adjusting everything so what you look at "directly" is sharp, and you don't really realize most of what is in your field of view is low resolution, maybe a bit blurry. Same when looking at something really close.

When you look at a picture, if some parts of it are blurry, your eyes/brain can't adjust so that it becomes sharp, because it was captured blurry. Even if you had a camera that exactly reproduces your eye, the pictures would look nothing like what your eyes see, because your eyes and brain are a very different system from a camera.

In photo there is something called "depth of field", which is "the distance between the nearest and the farthest objects that are in acceptably sharp focus in an image captured with a camera" [1]. You can see on the wikipedia page that there's an equation for approximating depth of field, that has in it 2u², where u is the distance to the subject. That means the closer the subject, the smaller the size of depth of field. You can test this with your eye. Take an object 30cm away, put your finger between your eye and the object, and you can change the focus of your eye between your finger and the object. When you focus on your finger the object is a bit blurry, when you focus on the object your finger is a bit blurry [2]. Now take two object that are 15cm away from each other, but 2m or more away from you. Changing the focus from one object to the other won't make the first object as blurry as when you did that close. This is because your depth of field is larger, as the distance increases.

Finally macro. In macro photography, you're often extremely close, so depth of field is extremely thin. When I say extremely thin, I mean "it can take 10 or more pictures to cover a whole fly". A solution in that case, to get all your subject in focus (sharp), is to take lots of different pictures, focusing a tiny bit closer/farther away each time, and then taking all the sharp parts of each picture. That's the technique used here, often called "focus stacking".

[1]: https://en.wikipedia.org/wiki/Depth_of_field

[2]: This might be harder if you're older, as we age we slowly lose the ability to adjust focus, hence the need for reading glasses (cameras can also use "reading glasses" when they can't focus close enough, they're called "close-up filters" and work the same).

When you take macro photos with close focus, your depth of field is like a very thin slice of the scene, you can think of it of having a plane of just a millimeter or so deep that you are scanning through the subject, taking a frame each time. So if your subject is something like a monarch butterfly which is generally around 30mm in length of body and close to 55mm considering both wings and body, you might need to take 60-70 frames then focus stack them afterwards to get critical focus on all parts of the subject.

I'm not sure what folks use now, but Zerene Stacker ( https://zerenesystems.com/cms/stacker ) was the gold standard when I was doing serious macro photography about ten years ago.