Why not always stop down if lenses are sharper there and blur the background later?
Asked 6/1/2012
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If many lenses are sharpest a few stops down, why would you ever shoot with a wide aperture if you could blur the background in post later? Ignoring exposure and shutter-speed advantages, is there still a real image-quality or rendering reason to use wider apertures? I'm asking specifically about in-focus image quality and whether digital background blur can truly replace the look of shallow depth of field from the lens.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
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Ignoring that fact that a large aperture lets in more light allowing faster shutter speeds etc. there are a number of reasons you'd want to use a larger aperture other than for subject background separation:
Wide apertures let you shoot through certain obstacles. It's a common technique in amateur motorsport photography to shoot through a chain-link fence using a wide aperture to blur the fence to the point where it becomes almost unnoticeable in the image.
Most wide aperture lenses are soft wide open, and this can be used for photographic effect, e.g. to give a softer, more flattering look for portraiture.
You get perfectly circular out-of-focus highlights when the lens is wide open as the aperture blades are fully retracted leaving only the circular hole of the lens barrel itself. When stopped down the aperture can take on a hexagonal/pentagonal shape, depending on the construction of the iris.
Finally it's worth reiterating that the "perfect photoshop" does not and cannot exist with regards to separating subject and background, and producing blur. Thus it will always be better to do it in camera.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
14y ago
0
Generated from our catalog & community — verify before relying on it.
No—stopping down is not always “better,” and digital blur is not a full substitute for optical shallow depth of field.
Many lenses do reach peak sharpness a few stops down rather than wide open, so if maximum sharpness across the frame is your goal, a moderate aperture often helps. But wider apertures still matter for several reasons:
- Real shallow depth of field is a 3D optical effect, not just “subject sharp, background blurred.” Parts of the subject itself can fall out of focus gradually, and backgrounds blur according to distance. A simple cutout-and-blur edit does not recreate that naturally.
- Wide apertures can help shoot through foreground obstructions, such as chain-link fences, by blurring them away.
- Wide-open rendering can be desirable creatively: some lenses are softer wide open, which can flatter portraits.
- Out-of-focus highlights can look different wide open, often more circular because the aperture blades are not stopping the lens down.
So: use a stopped-down aperture when you want more depth of field and often higher sharpness; use a wide aperture when you want the optical rendering and depth effects that post-processing usually cannot truly duplicate.
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