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I am fairly new to photography and I have read many "beginners guides" and watched youtube tutorials. One thing that remains elusive to me is how to properly pick what f-stop to use.
I use a 35mm, 55mm f1.8, and a 24-70mm f4 lens with my Sony A7.
For portraits, I generally try to pick lower f-stop like between (1.8-6f). For more general use like taking pictures of animals I usually pick between (6f-10f).
The issue I primarily run into is that when I take a picture with a lower f-stop, it looks great in my viewfinder. However when I go home to load it on a larger screen, I find that a lot of elements I am trying to capture is actually out of focus.
How do I know how much room I have to play with before a subject goes out of focus? It seems to change with f stop, how close I am to the subject(s), and the focal length I am using.
I understand the concept that I am basically focusing on a "slice" of space in front of me and when I lower the f-stop, this slice of space becomes narrower. I can't figure it out and I end up getting disappointed when I view the pictures on a large screen.