Understanding camera sensor and lens spots

Understanding sensor and lens spots - What they are, how to avoid and remove them.

As photographers, few things are more frustrating than finding ugly spots blemishing your otherwise perfect image. Whether you photograph landscapes, portraits, macro or creative techniques, dust and debris can show up on your photos in ways that range from subtle to seriously distracting. If like me, you are an ICM photographer, dust spots will probably be the bane of your life if you are shooting regularly above F16 in an attempt to balance longer shutter speeds with correct exposures.

I’ve just put this blog post together today, after going to have my sensor cleaned. I knew it needed cleaning, but was completely horrified when I saw how dirty my sensor and lens were combined! So, I thought I’d put a little bit of info together to raise your awareness of this ongoing challenge we all face.

Over the years, I have battled with dust spots and it continues to be an ongoing issue. As you will see later in the article, there are ways to try and avoid this annoyance and also ways to try and correct it, when you become aware of it. I have to admit, my go to option is still to have my lens professionally cleaned. I have tried the DIY option, and the freebie option offered by my local camera shop, but these don’t come close to having is done carefully and scrupulously by someone who knows exactly what they are doing!

In case dust spots are an enigma to you and you weren’t even aware they were possible, I’m going to explore the difference between sensor spots and lens spots, how they get there and what you can do about them.

Some of the many dust spots ringed in orange, and lens spots ringed in red on a recent ICM landscape image.

A great question to start with is whether dust spots really matter?

One thing to know early on, is that sensor and lens dust does not scratch or degrade the sensor or lens (unless you try to remove it incorrectly). It also won't cause overheating, electronic or manual failure. Unlike fungus or virus, it does not spread, although it can build up over time. Lens dust, while annoying, usually isn’t a big deal. The glass elements in a lens are designed to focus light from the scene onto the sensor. Because dust is far from the focal plane, small particles typically don’t appear in your images. However, excessive dust or smudges, especially on the rear element (the part closest to the sensor), can impact image clarity or contrast.

Sensor dust however, is more of an issue. It can affect your photos noticeably. If you don't pick it up at post processing, you may see it in prints or your images may be downgraded in competitions for its existence.

What Sensor Dust Does:

• It settles on the protective filter (usually a glass cover) above the actual sensor.
• It causes visible spots or smudges in your photos, especially at small apertures (f/11 or smaller).
• It may reduce image quality in certain scenarios, like landscape photography or macro work.

What are sensor and lens spots?

Sensor spots

Are marks or shadows caused by dust or debris that lands on the camera's image sensor. These are especially common in interchangeable lens cameras (DSLRs and mirrorless), where the sensor is exposed during lens changes.

Common signs of sensor dust include:

• Small, round or irregularly shaped gray or black spots
• Spots that appear in the same location on multiple photos
• Visible blemishes especially on bright, uniform backgrounds like skies or white walls

These spots become visible in your images, particularly:

• At small apertures (f/11, f/16, etc.)
• On light or uniform backgrounds (like skies, walls, or water)
• When shooting in bright environments

Sensor spots don't move between frames and stay in the same place regardless of the lens you use. They're a pain because they show up directly in the image data, requiring clean-up in post-processing.

Lens Spots

Lens spots are typically caused by dust, smudges, fingerprints, or moisture on the front or rear element of your lens, or even inside the lens barrel. Contrary to what you might expect, most dust inside a lens has very little effect on image quality.

However, large particles, water droplets, or fingerprints on the front or rear element can cause:

• Flare or ghosting in bright light
• Reduced contrast
• Hazy or soft-looking images
• Bokeh artifacts or visible blur spots in rare cases

The image made of my camera sensor at the start of the cleaning process!

To test your camera for sensor dust:

1. Set your camera to manual mode, and choose a small aperture like f/16-f/22
2. Point it at a clear sky or plain white wall.
3. Slightly defocus and take a photo.
4. Alternatively choose a longer shutter speed (so you have time to move your camera) and maintain the focus while making the image.
5. Check the image at 100% zoom. Sensor spots will be clear and fixed in place.
6. Look for dots, smudges and artifacts in the image.

I personally like to bring the images into Lightroom or photoshop and also increase the clarity of the dirt using the dehaze slider. The other thing you can do in Lightroom is when you have selected the 'Remove tool' bar and info you can tick the 'visualise spots' option to show the dust spots really clearly. This doesn't work so well for lens marks, but works great for sensor marks and dirt, which show up as white dots against the black background.

In Lightroom using the 'visualise spots' option - each of the sensor spots shows up as a small white dot.

Zooming in to 100% is essential to be able to see all the dust spots.

How Dust Gets into Your Camera

You might wonder how, on earth this dust gets in your camera. I certainly do. However I have been known to change a lens on the beach!!! And often forget to turn my camera off before changing lens. Dust can enter your camera system in several ways:

1. Lens Changes: The most common time for dust to enter is when you change lenses. Exposing the interior of your camera body to the environment allows airborne particles to get in.
2. Zoom and Focus Movement: Some zoom lenses extend and contract as you use them, potentially sucking in dust during operation.
3. Environmental Conditions: Shooting in dusty, sandy, or windy environments increases the likelihood of dust entering your camera.
4. Sensor Cleaning Failures: Many modern cameras have built-in sensor cleaning mechanisms, but they’re not always 100% effective, especially for sticky or oily particles.

Its great to know all about dust and spots but i thought it would be most useful to furnish you with a few handy tips to finish off the blog post. Firstly, some ideas on how to reduce the occurrence (prevention is always better than cure), and then some tips of what you can do if you do realise you have succumbed to the dreaded dust.

How to Prevent Dust from Entering

While it’s nearly impossible to keep your camera 100% dust-free, you can minimize the risk with a few habits:

1. Change Lenses Quickly and Carefully: Avoid changing lenses in dusty environments. Turn the camera body downwards during lens swaps to prevent particles from falling inside. Make sure you have your lens ready to place on the body, rather than taking one off then hunting around for the next. I find I prioritise the new lens getting on the body rather than packing the one I have just taken off into its bag safely. That I do when my lens and camera are safely joined.
2. Use Body Caps and Rear Lens Caps: Always keep the camera and lenses capped when not in use. If you loose any of them, there is no need to spend a fortune on the named brand caps - non brand ones work just as well and cost a fraction of the price.
3. Store Gear in Clean, Dry Conditions: Keep your equipment in sealed bags or cases. Silica gel packs can help manage humidity.
4. Use a Blower Before Lens Changes: Use a hand-squeezed air blower (like a Rocket Blower) to blow off dust from the lens and camera body before making a change.
5. Activate Sensor Cleaning: Many cameras have automatic sensor cleaning that shakes off dust on startup or shutdown. Make sure this feature is enabled. Once set up, you won't even notice you have it enabled.

Now, if (and inevitably when) you get dust in the camera, you will want to also know how to get rid of it. Although I stated earlier that I take my camera to be professionally cleaned, this is not absolutely necessary, if you are careful and patient and follow cleaning instructions to the letter. I am more than happy cleaning my lenses, but my sensor cleaning just doesn't seem to achieve the perfect results I want. The few times i've done it, i've used nearly a whole pack of swabs and spend almost as much as it would have cost me to pay someone!

How to Clean Dust From the Lens

• Use a Blower: Start with a blower to remove loose particles.
• Brush Gently: A soft lens brush can remove remaining dust.
• Lens Wipes or Microfiber Cloth: Use a clean cloth and lens cleaning fluid (or pre-moistened wipes) to gently remove smudges or fingerprints.

Always clean from the centre outward in a circular motion and avoid applying too much pressure.

How to Clean Sensor Dust

Sensor cleaning should be approached with care. Here’s a basic breakdown:

1. Use a Blower First: Remove the lens, hold the camera upside down, and use a blower to dislodge loose dust. Never use canned air—it can release propellant and damage the sensor.
2. Wet Cleaning: If dry cleaning doesn’t work, use a sensor cleaning kit with swabs and sensor-safe cleaning solution. Apply one or two drops on the swab and gently swipe it across the sensor. Use a new swab for each cleaning pass.
3. Professional Cleaning: If you’re uncomfortable cleaning your sensor, or if sticky particles won’t budge, take your camera to a certified service center. Most major camera brands offer sensor cleaning services.

Important: Always refer to your camera’s manual before attempting any cleaning. Sensor damage can be costly and void warranties.

Personally I have a dust spot acceptance level of about 10 spots! When I start having to remove more than this when I edit my images, I know it is time to book my camera in for a clean. I also know if I have an important shoot coming up, or one where there will be a lot of empty space such as big skies, and with ICM technique, I know that the dust spots are going to be a lot more noticeable. Whilst spot remove tools have come on leaps and bounds, the same can be said for a lot of photography - its a lot easier to get it right in camera than try and fix it later!

Its also worth mentioning that if you are getting your camera sensor checked and cleaned, why not get your lenses also checked for dirt, damage and calibrated to know you are working with the best that your kit can give you.

My beautiful clean sensor, after visiting Ton at ChipClean here in the Netherlands. Thanks so much for a great job today. https://www.chipclean.eu/