Photo stacking is the technique of taking several shots of a subject while slighty moving the focus to give the final image a greater depth of field.
These three photos were shot using a Nikkor 20mm 1.8G on a D500 body, each image consist of 15-25 separate photos that I then put together using the Helicon Focus software (it can also be done using Adobe Photoshop)
Key here is using a tripod.
I’ve had these cameras for a while (and two of them still have film in them)
(Click on the images to open them up)