this post was submitted on 26 Oct 2023
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Photography
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A place to politely discuss the tools, technique and culture of photography.
This is not a good place to simply share cool photos/videos or promote your own work and projects, but rather a place to discuss photography as an art and post things that would be of interest to other photographers.
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But what is this "speed" or "fastness"? The f-number is not just some abstract unit, but it's tied to physical reality.
To answer to that one needs to understand that this "fastness" refers to an exposure time (or shutter speed) one can use to achieve desired image quality. Thus f/2.8 on one format does not equal f/2.8 on another.
In principle f/4.2 on FF, f/2.8 on APS-C do an identical job - they give the same image quality (noisewise) with the same exposure time, the depth of field is the same and the blur from diffraction will be the same.