What causes small blurry spots in photos from a Sony A7C with a Sigma 24-70mm f/2.8?
Asked 1/9/2024
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I'm seeing a few small blurry spots in my images when using a Sony A7C with a Sigma 24-70mm f/2.8. The front and rear lens elements look clean, and I don't notice obvious dust on the sensor. The example image was cropped and zoomed in to make the spots easier to see. My settings were roughly ISO 250, f/6, and 1/200s. What is the most likely cause, and how can I check it?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
2y ago
2 Answers
2
Looks like sensor dirt.
This is more visible on clear pictures, with a closed diaphragm.
To check, shoot at something very clear (clouds, white wall, or your PC display filled with white), with a very closed diaphragm (f/22 or more), with the camera out of focus. Stains should show up at the same place in multiple shots, even with different lenses(*).
Very often a shot of air blower is enough.
Otherwise no need to panic if the sensor is a bit dirty, it won't show in most pictures, and is easy to fix in post production. When this becomes really annoying, then it's time to try your hand with a sensor cleaning kit or a visit to the service shop.
(*) The most efficient lens for this is a pinhole lens (very often DYI). Its equivalent f-number is close to 200 and this makes sensor dirt very visible.
Originally by user75947. Source · Licensed CC BY-SA 4.0
user75947
2y ago
0
Generated from our catalog & community — verify before relying on it.
The most likely cause is dust or dirt on the sensor, not the lens glass. Sensor dust often appears as soft, blurry spots and becomes easier to notice in bright, even areas of an image, especially at smaller apertures.
To confirm it, take a test shot of an evenly bright subject like a white wall, cloudy sky, or a white screen. Stop the lens down as far as possible (for example f/22), and deliberately defocus. If the spots appear in the same place across multiple shots, and even with different lenses, the sensor is the issue.
A blower is often enough to remove loose dust. If it persists, a sensor cleaning kit or professional cleaning may be needed. It’s also worth noting that minor sensor dust usually won’t show in most real-world photos and can often be cleaned up easily in post-processing.
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