I didn’t realize how good Photoshop had gotten with focus stacking. I use Photoshop CC but you may be able to do this with other versions.

1. Take a series of photos of the same subject focusing on different points each time. By using f/8 or wider you will get even sharper focus than f/22 in one shot. Plus, you can really tweak the areas.
2. In Photoshop, File > Scripts > Load files in layers – you will need to select the images at this point  (this will open all your pix in one file, each on its own layer
3. Select all layers and Edit > Auto Align layers
4. Keep them all selected and Edit > Auto Blend layers
5. Voila!

Three initial images:

Some uses:

1.macro for greater depth of field

2. You may have a subject that calls for great depth of field like a big bush, but something behind it is really distracting and you want it blurred.  So, if you use a setting like f/16 you will often get the back ground blurred too.  By using focus stacking you can use f/6.3 for example and get each part of the bush in focus but the background will stay nicely blurred.

3.In low light you may not want to have a really slow shutter speed. Using this method you can use a wider opening with faster shutter speed and take multiple images to blend later.

NOTE: Photoshop does a good job at aligning your layers in case you are off tripod.