I see spots: A hands-on guide to sorting sensor spots
No matter how careful you are, it’s inevitable that at some stage you’ll end up with dreaded dust spots on your camera sensor. Of course, you could always ignore the issue and just shoot away, knowing you’ll have a bit of post-production cloning to do when you get home, or maybe you have access to another camera body.
But what if you don’t have these luxuries? Here are five techniques that’ll help you banish them for good next time you’re in the field.
1) Shoot wide open
The thing about sensor spots is that normally they are caused by an object like dust that isn’t sitting on the camera’s light capturing photo sites per se, but on the protective glass that covers them. Because of this, what you normally see as sensor-spots are the shadow of the offending material being cast onto the photo sites.
That’s a good thing - contaminated photo sites are expensive to fix, and dust ‘on’ the sensor is easier to clean when you can. But most importantly if you’re in the field, if you reduce your f-stop by opening your aperture, the light coming in is from a wider angle and so the shadow cast will be more diffuse and therefore less noticeable.
2) Shoot visually complex scenes
It’s not uncommon for most people to first notice sensor spots when they shoot something visually ‘flat’, such as a clear sky or a smooth surface. That’s because sensor spots are normally so small, they get lost in the detail of the images.
In this case, another in-field work around is to try and shoot images that are visually complex (i.e., with no clear sky, or flat walls). More complexity and texture in your images will effectively hide the spot in the image detail.
Alternatively, if you know where your spots are, you can move your frame slightly so at least they are concentrated in a complex location.
3) Get creative - introduce motion blur
Building on my previous tip, you can also try to make a visually simple scene complex by introducing motion blur.
There are several ways to do this (and I’ve written about this before in ‘Life in the slow lane’, here), but basically by slowing the shutter down and either panning, or having the subject move the movement can increase the visual complexity of the image and help disguise the sensor spots.
At the time I captured the image below, my sensor had over 15 spots.
4) Increase your ISO
I know many people recoil at a suggestion to deliberately increase ISO, but surprisingly, as sensor noise increases, the visual impact of sensor dust diminishes.
I’m honestly not sure about the physics of why this happens, but I guess it’s because as the image gets grainier, the spot effectively gets broken up by the grain - a bit like looking at a mark on a window though fly wire screen.
Full disclosure: I’ve never used this technique professionally!
5) Shoot in crop mode
Finally, depending on where your sensor spots are, whether you can sacrifice file size, and if the spots (or the majority of them) are near the edge of the frame, you can also consider shooting in crop mode.
I had an issue recently where I had just one annoying spot near the bottom edge of my image. As the images didn’t need to be huge files, by simply moving to crop mode I had a quick and easy work around that literally cut out the problem.
A few more points (for the obsessive!)
- Shoot using electric shutter if possible. Every time a mechanical shutter fires it creates friction which can cause small particles to be created. Shooting with the electronic shutter eliminates this contributing factor.
- Only use prime lenses or zooms with a minimal bellows effect. The ‘bellows’ effect is what I call the phenomenon of air being sucked in and blown internally every time you change your zoom and is something I especially notice with zooms whose barrels extend out. To see what I’m talking about, try holding the rear end of your zoom (cap off and when not attached to the camera) close to your hand, and zoom in and out: You’ll feel some air move against your hand. When attached to the camera, this air is not blowing against your hand but against the sensor. I’d imagine the better the weather sealing on the lens, the less dust that can get in, but I’ve known people who have never taken their zooms off their cameras, but still end up with sensor dust spots over time
- Keep a 1.4x or 2x tele-convertor mounted on the body. Adding a tele-convertor effectively seals the body and sensor from the outside world (even when changing lenses), and so effectively eliminates the chance of dust entering from the outside. Of course, there can be optical downsides to adding another piece of glass if you don’t actually need it, however I have used this technique when I know I’ll be changing lenses in super dusty conditions, and the focal range I’m playing in works (e.g., using a 1.4 x tele-convertor changing between a 70-200mm and 100-400mm etc.). And a rant - why don’t camera companies make a 1x that can permanently sit there, just like a protective lens filter, but for the sensor!?
- Store equipment in clean zip-lock bags when in the field. I find this a great practice when in the field, not only because it helps keep lenses clean, but also adds another level of protection from water. Don’t however leave them in sealed plastic bags when at home, as long term any locked in moisture can increase the chance of fungi growing on elements
- Don’t change lenses after moving from a warm environment to a cool environment, or dry environment (e.g., air-conditioned room) to a humid (e.g. outdoor) environment. Whilst this will not cause sensor dust, any temporary condensation that may occur on the inside of your camera and sensor (and you’ve probably seen this effect when the front element of your lens has fogged when you’ve rapidly changed environments, can increase the possibility that any dust particles on your sensor stick more securely making them harder to get rid of
- Proactively get a professional clean every now and then. A good professional clean usually involves more than just cleaning the sensor, and should also involve cleaning the area around where the sensor sits. Remember how blowing dust off a sensor doesn’t mean it’s not in the camera? Well, a full clean means there shouldn’t be any dust left lurking around in the body, waiting to drop in just as you are about to take a Pulitzer-prize winning shot.
The post-production fix
If you do find a spot on your image, you can of course clone them out using something like Photoshop, but if you use mainly Lightroom (and I do), I find it super easy to use the ‘visualise spots’ feature. You use this by simply going to the spot removal tool (it looks like a band aid, and the shortcut is Q) in the Develop panel, click on that, and then the bottom of your screen you’ll see under your image a check box titled ‘Visualise Spots”.
If you check that, and then as you move your slider to the right, if you have spots on a clean background (remember visually complex backgrounds hide spots), you should see the appear. From here you can then zoom in (by holding the space bar down and clicking on them), and then use clone out as you normally would.
One other tip: If you have spots on one image, you’re most likely to have them on other shots, so rather than repeating the process for every image, just copy what you have done and paste the action by clicking ‘Cmd C’, checking the ‘Spot removal’ box, going to grid view, selecting all the other images which may have spots, and hitting ‘Sync settings’ (bottom right) ensuring the ’Spot removal’ box is ticked.
Final thoughts
Sensor spots are annoying at the best of times, and of course it’s always worth doing what you can to prevent them from happening, and also checking your sensor regularly before you take your camera out; Shoot the sky or a flat wall at say f20 will help you see if you have any.
But spots do happen, and you sometimes you only discover them in the field, when there isn’t a lot you can do about them. I hope at least some of these strategies help ease the pain!
About the author: Doug Gimesy is a professional award winning conservation & wildlife photographer based in Melbourne. See more of his work at gimesy.com, and on instagram @doug_gimesy.