Why do these photos look soft and “glowy” — focus, depth of field, or chromatic aberration?
Asked 4/21/2021
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I shot these with a Nikon D60 and a 55-200mm f/4-5.6 Nikkor, no filters, ISO 200, and the aperture wide open. In both images, some edges look blurred or glowing, highlights seem harsh, and parts of the frame look softer than expected.
Is this mainly chromatic aberration, or is it more likely a focus/depth-of-field issue? Also, if the photos were taken through a window, could a fine mesh or screen close to the lens and far out of focus reduce sharpness or add to this effect?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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The primary reason both images look blurry is because in both of them the point of sharpest focus is closer than most of the scene. Shooting with a wide open aperture minimizes depth of field, so things not at the focus distance get blurrier and blurrier fairly noticeably as they are further behind or in front of the focus distance.
In the first image the sharpest area is the junction of wires at the far right center. Since the top wire, upon which the squirrel is running, appears to move away from the camera position the further left in the frame it goes, it quickly become blurry enough to be noticeable. Everything behind it will be even blurrier.
In the second image, the twigs in the foreground on the right are the most in-focus part of the photo. But even there, it seems the actual focus distance was just in front of or just behind them. Everything in the background is well behind the focus distance.
Most of the highlights in both images show vertical and horizontal diffraction spikes. These could be easily explained by shooting through a mesh screen that has wires running vertically and horizontally. It's more noticeable in the top image because there are more highlights and they are brighter than the highlights in the second image. Diffraction affects not only the highlights, though. It also affects the darker parts of the image. Light passing very near to objects like aperture blades or wires in a mesh screen will be scattered by the obstructions. This is because of the wave nature of light's energy.
Here's what looking through a very fine screen at a single pinpoint of laser light looks like.
Now imagine that there are millions of pinpoints of light on the other side of the screen and the scattered patterns from all of them are overlapping each other. That's what is going on in your photos.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
5y ago
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This looks primarily like missed focus plus shallow depth of field, not just chromatic aberration.
In both photos, the sharpest area appears to be closer to the camera than most of the scene. Because you shot wide open, depth of field was limited, so subjects in front of or behind the focus point become noticeably soft. That softness can make edges appear to “glow,” especially around bright highlights.
Chromatic aberration may add a little color fringing on high-contrast edges, but it would not be the main cause of the overall blur and softness you describe.
A window screen or fine mesh near the lens can also reduce contrast and apparent sharpness, even if it is very out of focus. Shooting through glass can further increase flare or harsh-looking highlights, depending on angle and reflections.
So the most likely combination is:
- focus landed on something closer than your intended subject,
- wide-open aperture gave shallow depth of field,
- shooting through a window/screen may have lowered contrast and added softness.
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