How to avoid dust spots on your images, and how to remove them if it was too late
Welcome to the wonderful world of dust and software. The epic battle between the physical and digital world. Or how a simple piece of dust can spark a shopping spree.
The above paragraph makes no sense to you? Fear not, it is easy to explain.
What are sensor spots?
Here is a test image. Can you spot the spot(s)? Looks clean to me.
Let us look closer. Zoom in to 100% magnification, left upper part of the image:
That is an older image, so I can’t check anymore if these spots are sensor spots, but they appear like them.
So what is a sensor spot?
A tiny piece of dust stuck to the filter in front of the camera sensor causes a shadow on the sensor. The shadow is now visible on the digital images the sensor produces, until you or the camera remove the dust. Depending on the aperture of the lens, the shadow is more pronounced (small Aperture, e.g. f/16) or barely visible (large Aperture, e.g. f/1.8). For simplicity, I will continue to call it “dust on the sensor”.
If you feel the urge to remove the lens and blow the dust away, please don’t do it just now. You will only end up having more of that stuff on your sensor. Let us explore what we need to fix the issue, without causing mayhem.
Remind me, why do we not want dust on the sensor?
Before we move on to the solution part, we should stop for a second and think about why we want to get rid of the spots. They don’t harm you, right? Tiny insignificant pieces of dust don’t cause skin rash, do they? Well, they might, if you are a competition judge looking at sensor spots on competition images, but that is a topic for another day and has been covered more than it should have.
Do not fix something if it is not broken. It is only broken if the spots bother you or the judge at your photo club competition night.
But think a little ahead if you want to print your images in a beautiful large format. It will enlarge every microscopic thing. You see where I am going with this? A spot I can barely see on a 10cm x 15cm print does not bother me. But on a 1m x 1.5m print it will be highly visible and incredibly expensive if you need to re-print that monster.
Dust on the sensor does not come off on its own unless you remove it. It continues to spoil each of your images until the death of your camera, or your own, whatever comes first.
That was dark.
I assume your camera dies earlier. Or more likely: you buy a new camera (voice from the off: “No! Only over my dead body!”). I’m digging a hole here. I need some space to free my thoughts…
Where was I? Ah, sensor dust not coming off, that’s why we don’t want it. It stays there. Yes. Difficult to remove.
How to prevent dust from entering the inside of your camera
What can we do before it is too late?
How can you prevent the dust from entering the holy halls of sensor enlightenment? Don’t take the lens off. That’s easy. But what would you then do with all the other 10 lenses you bought when you were giving in to your GAS (Gear Acquisition Syndrome)? Sell them? (a voice from the off shouts “YES! Sell them and buy us a house instead!” That was the voice of your significant other, if you have one). Where was I? Right, the lens attached to your camera. You will remove it eventually to make use of all the other 10 lenses you negotiated over decades with your significant other (better?).
When you take the lens off, hold the camera facing downwards. Dust reacts to gravity and sinks down. Not always, e.g. when you blow into your camera. But mostly. I think.
Where was I? Using my 10 lenses, yes. Don’t expose your camera sensor for long, dust will find its way into the camera body. And make sure the part of the lens which faces the camera body is dust-free when you re-attach the lens.
Some camera manufacturer invented ways to get rid of sensor dust by vibrating the filter in front of the sensor, shaking the dust off. I once had a Canon digital camera, it boasted the “EOS Integrated Cleaning System (ICS)”. It worked well, I had no issues with sensor dust. Look up your camera model if it has something like that, Canon is not the only manufacturer who does that.
If you are keen to read what the manufactures do to prevent the dust from sticking on the filter, read the technical article on Canon’s website: EOS Integrated Cleaning System (ICS) (Note: The article is no longer on their current website, but you can access it through the brilliant internet archive, the ‘waybackmachine’) . It is worth reading, but brace yourself to read about “fluorine coating”, and “static charge” and “lens cap material” and “piezo-electric” and “ultrasonic vibrations”. Fascinating!
But whatever you do, dust will find its way on to the sensor. How do you remove it? That’s where the shopping spree comes in.
How to remove dust from inside your camera
Buy a sensor cleaning kit. And magnifying glasses with light, if your eyes need help to look at tiny things at a close distance. My set looks like that:
I bought it because I thought I had a sensor spot, but it somehow removed itself before I had the chance to use the kit. I used the magnifying glasses for other things, like removing splinters from my finger, but that is another story which has nothing to do with photography.
At the time I wanted to remove my sensor spot, it was not there anymore. I researched how to do a test (see below), and ended up not cleaning the sensor with the kit. Because of that, I cannot tell you if it works. Or how it works. I can still point out several things you want to think about before you buy a kit.
- What sensor size does your camera have? The kit swab needs to fit the sensor.
- Be reasonably sure that you have a sensor spot.
How to test for dust on the sensor
You can test for dust on your sensor with a simple procedure, create an ideal environment for the dust to thrive, and then take an image:
- Use a uniform light background for the subject — a piece of white paper is sufficient.
- Select a small aperture (high f/ number, e.g. f/22) — put your camera in aperture priority mode to select the aperture.
- Turn on manual focus and focus into the distance.
- Take an image of the white paper, let it fill the frame, you want a white image.
- Inspect the image at 100% magnification to see if you can find spots, Adobe Lightroom has the visualize spots function, that is helpful (see instructions further below).
If you are lucky, or maybe you are just starting out and you have only one lens and you never take it off, then you have no spots at all. Or your camera was able to fend off any dust. But if you have spots, then your software comes to the rescue.
We are now at the point where everything is too late. The sensor spot found its way on to the images you have taken already. Could be one image. Could be several thousand. Let us hope that it is a small number, and you already removed the dust from the sensor so it will not continue to be an issue.
How to remove sensor spots from your images with Adobe Lightroom
If we continue the example from above, we can quickly fix the issue by using Lightroom. Switch to the “Develop” module, it should look like this:
- “Develop” Module
- Select the “Spot Removal Tool”
- The “Visualize Spots” tick box is here
- Slider for sensitivity of (3)
Tick the “Visualize Spots” box and watch what happens. The image turns into a Black & White image with very exaggerated contrast. Use the slider to change the effect until you get rid of the noise and only see the spots.
Can you see the spots now? You see many spots now, not only sensor spots. It is very easy to remove the spots, just tweak the size of your (now circular) cursor. The inner ring should just cover the spot. Click to remove the spot.
The program now searches for an image area it can paste over the spot. Watch the animated GIF (it runs in a loop) to see how it works:
Now you know
- what sensor spots are and what causes them
- why you do not want dust spots
- how to avoid getting the spots
- how to detect if you have dust on your sensor filter
- how to remove dust from the filter
- how to remove dust spots from your images with Adobe Lightroom
Have fun taking pictures… spotless!