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Sensor Cleaning
22 October 2018
We feel obliged to confess that last week we spent a few minutes cleaning the sensors of two of our most used cameras. It's a confession not because we've sinned but because we don't want to hide anything.
Tools. Bearing down on the problem with Eclipse (top), SensorSwipe (the white stick) and Giotto Rocket (right) with a Carson magnifier.
What we don't want to hide is, well, two things, really. Both about sensor cleaning.
TWO THINGS
One is that we don't clean our sensors very often. Not even annually. The theory is simple: if it isn't dirty, don't clean it.
We're very careful to avoid introducing problems when we change lenses (which we do a lot, for every shoot almost but rarely in the field). And we're usually shooting at larger apertures, which makes any minor sensor dust invisible anyway.
The other is that it's inevitable that something will get stuck on the sensor of an interchangeable lens camera. If not from exposure when changing lenses then from the shutter flipping up so many times.
Dust. An f8 aperture revealed this dust spot on a uniform background shown here at 100 percent. If you can't see it, move back a bit from your screen.
There are a few more things we'll confess but those are the big ones. You don't have to do it as often as you think if you're careful but you do have to do it.
CAMERA OPTIONS
This goes even for cameras that have sensor cleaning options in the menu system. The truth is that option just wiggles the sensor (point the camera down), which will not dislodge specks that are stuck to the glass.
And it's especially true for mirrorless systems which don't, as a rule (Canon R excepted), have any protection when you remove the lens.
It may make you nervous to think about manually cleaning a sensor but it can be easier than cleaning a window.
SEEING THE PROBLEM
First of all, you need some help seeing the problem.
To see it on an image, take an unfocused shot of the sky with your lens stopped down to f16 or more. And just for fun, try the same shot wide open so you can see how aperture affects it.
What may be obvious at f16 against that uniform image is usually invisible at f2.8. And where the field is not uniform (say a busy landscape with little sky) you may never notice it.
Note that spots that appear in the top of the image will be found at the bottom of the sensor. That's how cameras and lenses work.
But that shot serves just a reference point and, perhaps, an occasional test before any important shoot.
When you lock up the mirror on a dSLR or take off the lens on a mirrorless camera, you're going to need some help to see the problem. That calls for an illuminated magnifier.
Sure, you can fiddle with a desk lamp and magnifying glass but the $7 Carson PO-25 3x MiniBrite Lighted Magnifier is worth every nickel.
We've used one for years to see both what the problem is and to confirm that we've successfully eliminated the problem.
TOOLS
We used to review this stuff and we saw some great ideas that were, in practice, horrible failures. Never, for example, touch your sensor glass with any adhesive.
The $10 Giotto Rocket is a universally recommended product and we do have one. In all the years we've had it, though, it hasn't been much help. Either the dust on the sensor is unmoved or it adds a fine spray of dust. Its one advantage is that you can take it on a plane.
We used to think it was wiser to vacuum out the dust rather than puff at it. And if you have a strong enough vacuum, that makes sense. But puffs are stronger. And in a pinch, the Rocket can help. Maybe not much more than a built-in sensor cleaning function, though.
In any case, it isn't guaranteed to work. For that you have to use a different approach.
WET CLEANING SUPPLIES
There are those who swear by brushes of one kind or another, but we've never had any luck cleaning glass (windows, mirrors, light tables or any other kind) dry. So we'll skip that all together in favor of a safe wet cleaning.
For that you will need 1) a quickly evaporating solution and 2) a lint-free cloth 3) bound to a cleaning tool of some kind.
This is a specialized sort of lens cleaning in which you want to minimize contact with the glass (which is why you want a fast evaporating, gentle fluid) but in a very constricted environment (which is why you need a tool).
You can use isopropyl alcohol but it can be slow to evaporate, leaving streaks. The best recommendation for optical cleaning is a solution of 60 percent acetone and 40 percent methanol. The methanol slows down the evaporation of the acetone so it can dissolve the dust.
But you don't need to be a chemist. This stuff is easy to find online. Here's the shopping list:
- Eclipse Cleaning System Solution ($11.40)
- PEC-PAD Lint Free Wipes ($9.89)
For the cleaning tool, you can cut a piece of art board the width of the narrow dimension of your sensor and long enough to provide a handle to sweep the business end across your sensor from outside the camera.
You might also find that a plastic knife handle is just the right size for your sensor.
We use a SensorSwipe we bought from Copper Hill Images long ago. The company no longer seems to be selling its sensor cleaning kit, however.
The cleaning solution and pads are both lifetime supplies, by the way.
CLEANING
Cleaning is a two-step process.
- First, blow off any loose dust with the Rocket or a can of compressed air (light touch only, though).
- Fold a wipe tightly over your tool and anchor it with a rubber band before applying a few drops of fluid on the edge and wiping across the sensor.
Use a light touch. You should be sweeping across the sensor smoothly, leaving a wet streak that dries almost immediately.
Take a look at the sensor with your magnifier to see if it's clean. If not, repeat step two.
Some methods recommend replacing the wipe every time you clean the sensor. And they're cheap enough (you get four out of each piece) but it's a nuisance. We confess to reusing the wipe twice to remove light dust with no ill effects. After that, you risk redepositing debris.
CHECK YOUR WORK
You can confirm the cleaning the same way you discovered it: by taking a shot of the sky stopped down.
But if you used an illuminated magnifier, you'll already have confirmed the sensor is clean.
CONCLUSION
It didn't take us long to do this after we discovered the problem. And we probably won't have to do it again for a long time.
But when you have to do it, you have to do it.