How can I quickly check for sensor dust during an outdoor shoot?
Asked 11/15/2019
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I found a gray spot in about 20 outdoor photos, but I didn’t notice it through the viewfinder or on the rear LCD while shooting. It shows up clearly against the sky. What’s the fastest way to detect this kind of problem in the field, and are there any practical steps to reduce or avoid it?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
32
The dust isn't on the lens — it's on the sensor. Dust on the lens will not resolve so clearly.
To check for it quickly, set your aperture to the smallest your lens can support. (Small apertures have large f-numbers, like f/22.) This will keep the light striking the sensor to a straighter angle, which in turn will make the dust (which sits on filter layer right above the sensor) resolve most clearly. Then, take a picture of something bright — plain blue sky is ideal.
Any dust should jump right out. In most cases, the built-in sensor cleaning will shake that off, but it's a reasonable idea to carry a (high quality) rocket blower if it needs a bit more. And if that doesn't work, make note of it (keep your test frame!) and resign yourself to touch-up in post
Note that the opposite to the above on aperture applies — if you shoot at wide apertures, any dust will be less apparent, and may even be completely hidden in some scenes. This is actually why the dust isn't apparent in the live view image on the LCD: what you see there is done with the lens wide open even when the aperture is set to close down for the picture. If you know already that you're dealing with this, you can plan to use a wider aperture so the dust is also less obvious in the captured image.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
6y ago
0
Generated from our catalog & community — verify before relying on it.
That spot is most likely sensor dust, not dust on the lens. Sensor dust becomes most visible at small apertures such as f/16 to f/22, especially against bright, plain backgrounds like blue sky.
A quick field check: stop the lens down to its smallest aperture, photograph a bright uniform area (sky works well), and review the image enlarged on the LCD. Dust spots should show up clearly. If you want to confirm whether normal photos will be affected, remember that dust is usually much less visible at wider apertures; often it won’t show much above about f/8.
To reduce the problem:
- Use the camera’s built-in sensor cleaning.
- Carry a good rocket blower for loose dust.
- Avoid changing lenses in dusty environments when possible.
- Add a sensor-dust check to a pre-shoot checklist, especially if you change lenses often.
If you discover dust during a shoot and can’t remove it, keep a test frame so you know where the spots are and plan to retouch affected images later.
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AI6y ago
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