Today’s Question: How can you tell if dust spots are on the sensor or on the lens? For sensor dust, how effective is the in-camera cleaning? Is the dust mapping feature useful? And should I consider cleaning the sensor myself or leave that to the professionals?
Tim’s Quick Answer: If you actually see a dust spot in a photo, it is most likely something on the sensor. In-camera sensor cleaning is helpful for basic dust, but won’t resolve all issues. I don’t consider the dust-mapping feature particularly helpful. Instead, I recommend cleaning the sensor yourself if you’re comfortable, or sending the camera in for a professional cleaning if you’re nervous about doing it yourself.
More Detail: When you see a clear dust spot in a photo, it is typically a clear indication that the image sensor on the camera needs some attention. If the dust is on the lens it will most likely not be visible in the photo at all. If it is, it will more often than not appear as an out-of-focus blemish that is darker or brighter than the surrounding area. For example, if there is dust on the lens and you photograph into the sun, those dust spots will create bright areas similar to lens flare.
For a blemish on the image sensor, especially if the lens aperture is closed down to a relatively small size (large f-number), the dust spot in the photo will look relatively crisp and dark (since it is blocking light from getting to the sensor).
The in-camera sensor cleaning can help remove dust that hasn’t gotten too stuck to the sensor yet, such as dry bits of dust that are mostly being held on by static. To assist with this type of dust issue I do recommend enabling the automatic in-camera sensor cleaning, which will generally run whenever the camera is turned off.
However, for dust that has combined with moisture to get stuck to the image sensor, the in-camera cleaning will likely be ineffective. In this situation the sensor needs to be cleaned directly.
If you’re comfortable performing this relatively delicate work yourself, it isn’t too difficult. However, cleaning your own sensor may void your camera’s warranty, and there is obviously a risk that you might damage some of the delicate components in your camera.
If you are comfortable cleaning your own sensor, I recommend the swabs and solution from VisibleDust (https://timgrey.me/visibledust). I use the kit that includes several swabs, the cleaning solution, and a sensor brush. Just be sure to select the correct size for your specific camera, and review some of the videos and other details published by VisibleDust to ensure you’re using the right technique when cleaning the sensor.
When cleaning the sensor yourself you want to use only a very small amount of the cleaning solution, and you should only use the swab with one swipe in each direction before discarding the swab. If that doesn’t resolve the spots on the sensor, use a clean swab to try again.
You can find the VisibleDust sensor cleaning package here, but again be sure to select the correct size for your specific sensor size:
https://timgrey.me/visibledust
And if cleaning the sensor yourself makes you nervous, you can send the camera in to the camera manufacturer or a company that specializes in cleaning camera sensors so that you don’t have to risk damaging your camera.