Focus stacking is a digital process by which multiple images (of the same composition) are combined by selecting the sharpest section of each picture. The goal of the process is to get an image that is sharp at both close and long range.

Why not shoot with a small aperture?

While it is possible to achieve similar result using a small aperture (ex: f/32+), doing so produces diffraction which reduces image quality. To maximize image quality, it is preferable to shoot at the lens sharpest aperture (generally around f/5.6 – 8) and stack the images.

How to create stacked images?

Here is a list of the most popular software to do focus stacking:

I have not found any good and easy to use free alternative. Anyone knows of any?

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planetMitch

chief astronomer at planet5D LLC
Mitch "planetMitch" Aunger is the creator and mastermind behind planet5D.com — which covers every aspect of HDSLR cameras (and a whole lot of other cameras as well). A lover of photography since his early days, he graduated to selling stock photos to make a little bit of spare cash. It wasn’t much, but it allowed him to upgrade to better cameras as well as computers, and it wasn’t taking money away from feeding his family.
He loves the stories that the still image can tell. In the summer of 2008, he read a story written by Arnold Kim called “I Quit My Job” — Arn is the owner of macrumors.com. He started macrumors in 2000 as a hobby, and by 2008 he was making more money with the site than he was on his day job, so he quit. The surprise to the story is that he was a doctor making more than six figures! Right then and there, planetMitch dreamed about doing the same thing.
September 2008 rolled around, and Canon announced this new version of the incredible 5D — the Canon EOS 5D Mark II. It was the first Canon DSLR to shoot full HD video and the earth moved! (It really was a huge deal in the photography world.) planetMitch knew if there was ever a chance to ride a wave of something he was really passionate about, this was it — and the blog at planet5D.com was born. It is now one of the most popular HDSLR blogs on the planet, and he is making a full-time living from blogging. He couldn’t be happier!
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