Why are my low-light photos soft with a Canon 60D and 50mm f/1.4?
Asked 9/30/2013
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I shot indoor, low-light photos on a Canon 60D with a Canon 50mm f/1.4 USM and the results looked much softer than usual when viewed on my computer. Settings were f/1.4, 1/160 sec, ISO 640, using a single autofocus point. In brighter conditions this camera/lens combo is often very sharp.
In these images, many areas look out of focus, and I also noticed strong purple fringing/chromatic aberration around the bright window edges. Is this likely a focus problem, lens issue, dirty filter/lens, or just a normal result of shooting wide open in low light?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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It seems to me that the image is quite adequately sharp given the lighting conditions. Some things affecting the sharpness of a photo in low light:
Almost any lens is going to be somewhat soft at its maximum aperture. As far as I know, the Canon 50mm/1.4 at f/1.4 is a bit on the soft side relative to other fast primes (even compared to the cheapo 50mm/1.8!)
The larger the aperture, the tighter the depth of field - most of the things in your photo are simply not in focus due to the razor-thin DoF at f/1.4.
The less light, the less contrast and the less accurate the autofocus mechanism is. And the larger the aperture, the easier it is for even a tiny focusing error to throw the focal plane slightly off.
Related to the previous two bulletpoints, moving the camera even slightly (eg. when doing "focus-and-recompose") might well be enough to cause noticeable misfocus. Using the non-center autofocus points might help, but they are often less accurate than the center one.
The higher the ISO, the softer the image due to noise reduction. This is something that can be tweaked in post-processing if you shoot RAW, but it's always going to be a balancing act between noise and softness.
Originally by user14547. Source · Licensed CC BY-SA 4.0
user14547
12y ago
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This is mostly normal for that setup and scene, not necessarily a defective lens.
At f/1.4, depth of field is extremely thin, so only a small slice of the scene will look sharp. In your example, the focus appears to be on the table corner/lobster bib area, while objects slightly nearer or farther away soften quickly.
Also, many lenses are softer at their maximum aperture, and the Canon 50mm f/1.4 is known to be less sharp wide open than when stopped down. Low light also makes autofocus less reliable because there is less contrast to lock onto, so even a small focus error becomes obvious at f/1.4.
The purple fringing around the bright window is typical chromatic aberration from extreme high-contrast edges, especially in a wide-open shot. It can often be reduced in post, particularly from RAW files.
So the main causes are:
- shooting wide open at f/1.4
- very shallow depth of field
- harder autofocus conditions in low light
- high-contrast window edges causing CA
If possible, try stopping down a bit, increasing ISO, and checking focus carefully on a specific subject plane.
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