End to End Process: Macro Stacking on the Canon 90D, Lightroom Classic and Photoshop.
Part 1: Set up the Canon 90D to do Focus Stacking
1. Turn the camera on and flip open the screen.
2. Press the Start/Stop button.
3. Press Menu.
4. Go to Shooting Menu 5 (the red pages).
5. Press 'Focus bracketing' on the screen (currently Disabled).
6. Select Enable.
7. Press 'Number of shots' and up the number to your requirement.
8. Change the 'Focus requirement' to set how far apart the shots will be focused and taken.
Caveats
A. You cannot use a flash for this process which can be an issue for macro photography.
B. After a certain point the camera will slow down with the image taking as the buffer gets full.
Part 2: Take some pictures
The pictures need to be steady, perhaps on a tripod or solid surface, unless you are really steady.
Part 3: Import your pictures onto your computer with Canon EOS Utility 3
(Assuming you have downloaded and installed the software)
1. Plug in the camera to your computer.
2. The EOS Utility will automatically open and download the images to you selected location.
Part 4: Select your images in Adobe Lightroom
1. Open Lightroom
2. Click 'File>Import Videos and Photos...'.
3. Locate the folder where the images are downloaded to.
4. Use CTRL or SHIFT with the mouse to select the images you want to stack.
5. Click the 'Import' button (the images now import into the application).
6. Again select the images to stack using SHIFT and the mouse.
7. In the menu, click 'Photo>Edit In>Open as Layers in Photoshop...'.
8. Photoshop opens and you can see all the images lined up as layers in the bottom right of the application.
Part 5: Finishing up in Photoshop
1. Select all of the images again using SHIFT and the mouse.
2. Click 'Edit>Auto-Blend Layers...'.
3. Leave 'Stack Images' selected and click 'OK'.
4. The images now merge and can take some time depending on the number in the set.
5. Once it is complete press 'CRTL+SHIFT+E', which will merge the layers into a single image.
6. Now save the image off.