The dept compositing function works by combining a series of images taken at different focus distances. You or the camera needs to adjust the lens focus between each frame. The camera settings; shutter, aperture and ISO should be the same for each of the series of images.
Many of the EOS R-series cameras include a feature called focus bracketing. This automates the process of moving the lens and can take a series of images at high speed. Some cameras can only save the individual frames, others can save the individual frames or make a single composite JPG with maximal depth of field.
Here's an example image...
I used an EOS R6 with EF 100mm f/2.8L Macro IS USM lens and shot the series using the focus bracketing function. Exposure was 1/60th f/4 ISO 100 for each of the frames and I set the camera to take 50 images. I made a composite using the depth composite feature in DPP which I saved back as a TIFF image.
Here's three of the 50 individual frames, they are intended show how limited the depth of field is in each of the images captured by the camera.
Here's the final image created from the whole set of images using DPP depth composite function.
I know there are some odd blurs on the left side of the picture along the green edge of the locomotive.
