Category Archives: Technique

Commentary, Equipment, Popular, Technique

DSLR Sensor Cleaning – My Approach

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Update: June 14, 2023 — I just returned to this article after not reading it for quite some time, perhaps years. I still think it contains useful information, and the steps I describe still represent more or less what I would do today. However, things really have improved when it comes to the dust issue. Back when I had a Canon 5D, dealing with sensor dust was a major issue that required frequent cleanings (often with wet cleaners) AND a lot of spot removal in post. But today that is hardly ever the case. It is actually pretty rare to encounter visible spots, and when they do show up the cameras dust reduction system often takes care of them and they disappear a few frames later. I still firmly believe in tolerating a tiny bit of dust and dealing with it when necessary by using the least intrusive methods first.

When I got my first DSLR (1)  I was very upset if I got any sensor dust in a shot. I was also very paranoid about cleaning the sensor (2), having read too many posts about how one can damage the sensor during cleaning. Now that I’ve used digital cameras for quite some time I’ve gotten over it and life is much, much easier.

Here is a summary of my approach (3) to dealing with sensor junk…

Rule #1: Modern cameras typically include dust-reduction systems that vibrate the sensor to dislodge dust particles. I set mine to operate automatically each time the camera is turned on or off. In addition to ensuring that the process runs regularly, this automatically runs it after every lens change, the time when you are most likely to pick up dust. You can also manually trigger a dust-reduction system cycle from the control menus, and I do this if I notice a dust spot while shooting. (If you have ever shot for a day or a few days without checking, only to realize that you had picked up a big dust bunny on day one and that it appears in all of your several hundred or more photographs, you will adopt this practice!)

Rule #2: I don’t worry too much about a small amount of dust in my images. I rarely can get a sensor clean enough to get perfect, dust-free shots at smaller apertures, and when I do the dust will soon return. Rather than obsess about dust-free perfection I quickly fix most small spots in post-processing. I can usually deal with most dust spots in a matter of a few seconds in Adobe Camera Raw (ACR) or Photoshop. (My preference is to do this in ACR during the raw conversion process. This fits better with my workflow which relies on the use of smart layers in Photoshop.)

Rule #3: When the dust gets to the point that dealing with it in post is no longer efficient, I try the easiest thing first. I use a blower to try to clean out the worst of the stuff. More often than not this is enough and I can go back to relying on rule #2. Point the tip of a good blower bulb into the chamber but keep the tip itself just outside. As you blow a few dozen puffs into the chamber and toward the sensor, change the angle of the bulb to ensure that you get full coverage. It is probably best to hold the camera with the open chamber facing down. (Don’t overdo it, since the blower can move some dust onto the focus screen of some cameras, leaving annoying bits of dust that do no real harm and will not affect your photographs but which are very difficult to remove.)

Rule #4: Sometimes rules #1-#3 aren’t enough and a more direct cleaning of the sensor itself becomes necessary. At this point I used to try a static charged sensor brush, being very careful to avoid letting the brush touch anything but the sensor* glass itself. Yes, the brush can pick up other stuff in the chamber, and I have learned from experience to avoid this. I still occasionally use the brush, but with the availability of the sensor gel products (4), these days I’m more likely to try them before I try a brush, though the brush can still be useful sometimes for stuff caught right up against the edges/corners of the sensor.

Rule #5: On rare occasions rule #4 fails, too. If the contamination is adhering too firmly to the sensor surface I resort to wet cleaning with Eclipse fluid and PecPads. I can rarely get it right in one attempt, so I plan on having to work at this a bit, but eventually I get a reasonably clean sensor with no streaks. Be very cautious to not use pressure, to not “scrub” the sensor glass, and to not use too much liquid. Let the fluid loosen and/or dissolve the material and gently wipe it off with the pad attached to the “spatula” tool. Read the instructions for this cleaning method very carefully before attempting it. It isn’t terribly difficult but there are a few ways you could go wrong including: pressing too hard and damaging the coating on the sensor glass, transferring lubricants to the sensor from other parts of the camera chamber, leaving streaks on the sensor.

Rule #6: On very rare occasions a combination of methods is required. Often the wet cleaning works well for me but leaves a few spots of dust on the sensor. For this reason I frequently follow the wet cleaning with a quick once-over with the static charged brush and/or the sensor gel stick.

From all of this, it might sound like I’m sensor-obsessed. I’m not. Remember rule #1 is the one I follow most. I usually go many months between real sensor cleaning sessions, and it is very rare for me to have to resort to a wet cleaning.

In my opinion, it is not necessary to fear the sensor cleaning operation as long as you are reasonably careful. Once you do it a few times it becomes quite quick and easy. Taking your camera to the shop or sending it to the repair facility is going to cost you a significant sum, take considerable time, and probably not result in a cleaner sensor in the end.

However, one photographer pointed out that he has a service plan that includes six free sensor cleanings per year. A few years ago, I would have counseled against relying on this – since early cameras without sensor cleaning systems often needed to be cleaned frequently and on short notice. However, the newer cameras rarely need a serious sensor cleaning – and in this case I can see how simply sending the darn thing in (while you keep shooting with your backup camera) could make sense for some people. (I still feel that you should be able to clean the thing in the field if necessary.)

Notes

(1) Interchangeable lens mirrorless cameras have become widely available since I first wrote this article about sensor cleaning. I use one along with my DSLR system, and both need occasional sensor cleaning — to the techniques described here are also broadly applicable to mirrorless cameras, too.

(2) I’ll anticipate that someone might feel obligated to write, “You aren’t really cleaning the SENSOR! You are cleaning the glass cover over the sensor, you nitwit!” Yes, I know that. It is just easier to refer to the whole assembly as “the sensor.” :-)

(3) Disclaimer: This report describes what I do, but I am not any sort of certified expert on these things – as I wrote, this is “my approach.” I strongly urge you to seek out and learn from other official sources of information on sensor cleaning and related issues. The inside of your camera contains fragile and sensitive electronic and mechanical components and it is possible to cause damage while working there. You should read and carefully consider warnings from the manufacturer of your camera and any accessories and tools you use on it. If you are not convinced that you are competent to do this work on your camera, you can always take it to a professional. I do not claim that my methods are the best or most appropriate, nor that they meet the standards of the manufacturers of the camera equipment nor do I recommend that you use my methods in place of manufacturers’ official recommendations.

(4)  The Sensor Gel product (available here) is a cube of a sticky gel attached to the end of a plastic “wand.” The gel cube is placed in contact with the surface of sensor’s glass cover, and the dust adheres to it. Since the cube is smaller than the sensor, this process is repeated across the sensor surface. Press the cube against a supplied sheet of “sticky paper,” to clean it. I tried the Sensor Gel Stick partially out of desperation, as my aging Canon 5DII had picked up a ridiculous number of dust specks that were resistant to other methods of cleaning. After the first cleaning there were no noticeable spots left on the sensor. I continued to use it during a four-day shoot in Death Valley, a location known for dust—and, again, the result was impressive. The product is not cheap, costing about $50 for the gel stick and the sticky papers. Frankly, I think it is overpriced—but because it works so well I was willing to pay the price. I have recently seen similar products online from other distributors at lower prices, though I cannot vouch for their quality.  I understand that two versions are currently available. One is the “blue” version that I have. The other “pink” version is apparently designed for certain camera brands, particularly for some Sony cameras. Check the product descriptions and make sure you get the right version for your camera.

(Most recent update: June 2023)

Articles in the “reader questions” series:

G Dan Mitchell is a California photographer and visual opportunist. His book, “California’s Fall Color: A Photographer’s Guide to Autumn in the Sierra” is available from Heyday Books and Amazon.
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Equipment, Software, Technique, Tests

A Test: Correcting Lens Distortion in Post-Processing

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Earlier this weekend I read a forum thread about the Canon EF 50mm f/1.4 lens, of which I have a copy. The thread lamented the barrel distortion of this lens (which I don’t really find to be that big of an issue) and continued with posts suggesting alternatives including software correction in the post-processing phase. One response to this proposal was that software correction would degrade the  image and would therefore be unacceptable.

That theory seemed sound and I have believed this to be true in the past, but I decided to test this idea for myself. Using an old photograph taken with this lens, I cropped a small section from one of the far corners – the worst part of the frame and, according to some, subject to a lot of softness and distortion on full-frame bodies like my Canon 5D. To make things a bit more challenging I used a photograph that included a bunch of dried california grasses – full of very fine details and high contrast.

I converted the original RAW file using ACR (Adobe Camera RAW) with no sharpening. In Photoshop I cropped to a section of reasonable size for web presentation, using that section from one of the corners of the image. Then I made a duplicate of the cropped section of the image.

In one of the two versions of the crop I used the LensfixCI plugin to correct for the slight barrel distortion of the EF 50mm f/1.4 lens. This $29 plugin* includes a database of many lenses, and also keeps a smaller databases of your lenses. It uses EXIF data to identify the lens (and focal length with zooms) used to take the photo and automatically applies optimum distortion corrections from its database. It takes me about 10 seconds to select the plugin and apply its changes.

* (I have left the reference to this plugin that I used when I did the test several years ago, even though I no longer use it. Today I simply use the built-in correction in Lightroom or ACR, where I apply lens- based corrections by default in virtually all cases.)

Next I used my normal sharpening methods on both images, inspecting the results and making adjustments as I applied them. In the end, as would typically be the case, I used slightly different sharpening settings for the two images – but that reflects the normal way of operating. Finally, I took the two images and placed them side by side in the single high quality jpg file that follows.

Barrel Distortion Correction
Barrel Distortion Correction

(NOTE: The version shown above on this page may have been downsized for formatting purposes, which limits the amount of detail that is visible. Click the image to view it at its original size, or follow this direct link to the original image.)

I have a darned hard time seeing any difference in sharpness, contrast, or color that might have been introduced by the correction process. If a difference is visible a) it is almost impossible to say which version is better, and b) the difference is almost certainly completely insignificant in an actual print. (Keep in mind that these are 100% crops of the worst part of the frame in the far corner – and that the area shown here would be a very tiny section of a full print that would be something like five feet/60″ wide.)

After doing this test, I’m not really concerned at all about any negative effects of using this method of correcting lens distortions, and today I simply allow ACR or Lightroom to automatically correct for such lens characteristics by default. And whatever the tiny negative effect on sharpness we might imagine to produce, it is far outweighed by the ability to straighten lines and so forth when necessary.

(Anyone care to guess which half contains the “corrected” version of the crop? Feel free to post a comment and an explanation of what you (think you) see… ;-)

(This 2007 post was slightly updated on 1/5/2013)

G Dan Mitchell is a California photographer and visual opportunist. His book, “California’s Fall Color: A Photographer’s Guide to Autumn in the Sierra” is available from Heyday Books and Amazon.

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Technique

Panorama: Dawn, Thousand Island Lake, Mounts Ritter and Banner

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It is now fairly common for DSLR photographers to produce very large images by combining (or “stitching”) multiple separate component exposures of a scene. With the right kind of subject (one that is fairly static) and careful technique this can be quite successful.

I’ve experimented in the past with stitched photographs. I’ve had some luck with hand aligning and masking individual photos, and I’ve played around with some third-party software designed for this task. I was pleased to find that a very competent stitching feature is now part of the newest CS3 version of Photoshop.

As an example of what you can do with this tool, I’ve uploaded a photograph I created earlier this summer. Shot at dawn at Thousand Island Lake in the Ansel Adams Wilderness Area, the photograph consists of five 12MP images. Click the thumbnail to see a larger version.

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Technique

From Here to Infinity?

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Greg writes:

I’ve enjoyed your photography that I’ve found on your three websites. I especially enjoyed your photos of the Sierras. While looking at your photo “RitterBannerEdizaFlowers2007_07_25.jpg” [see below] the question comes to mind, “How did he get everything from 12 inches to infinity in focus?”

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Mounts Ritter and Banner, Ediza Lake. Sierra Nevada, California. © Copyright G Dan Mitchell.

(Greg also noted that current Canon EF lenses generally do not include a DOF scale.)

Thanks for writing, Greg.

The main technique in this photo is the use of a short focal length wide angle lens. It (along with similar photos in my gallery) was shot with the Canon EF 17-40mm f/4 L lens, which is an ultra-wide angle (UWA) lens on the full-frame Canon 5D. Such UWA lenses can produce an extraordinary depth of field – it may not be quite “12 inches to infinity,” but it is pretty close.

In addition, one can shoot at smaller apertures on a full frame DSLR compared to the crop sensor DSLRs. On a crop body you generally avoid apertures smaller than f/8 or so, especially if you are planning to make a large print. At smaller apertures, diffraction decreases the maximum sharpness of the image. You get greater depth of field, but the cost is that the sharpest portions of the image in the plane of focus actually become less sharp than at optimal apertures. With a larger sensor (or larger film), diffraction doesn’t become significant at f/8. I conducted some experiments with my L lenses and 5D and discovered that sharpness in the plane of focus is at least as good at f/11 as it is at f/8, and that focus plane sharpness at f/16 is virtually indistinguishable from f/8 and f/11.

So, by combining a very wide angle lens (I believe it was 17mm in this photo) with a very small aperture (f/16 most likely) and focusing just beyond the closest object in the frame, I can achieve very wide DOF.

There are a few other tricks that one can employ. Faced with scenes that have an extremely wide dynamic range, I often take two exposures with one set for the darker areas and the other for the bright areas. In a situation where the foreground is dark and the distant objects light, I can also slightly shift the focus between the two exposures. (I combine the two images in post-processing; this is more or less equivalent to using ND grad filters at the time of the exposure though it permits more flexibility at the expense of an extra exposure.)

– Dan

BTW, Greg also reminded me of an interesting SF Bay Area show that is about to close:

P.S. You had an earlier post about the Yosemite art exhibit at Stanford. I’d like to bring to your attention another Yosemite exhibit that is currently running through Aug 26 (ends soon!) at the Oakland Museum (http://www.museumca.org/). This is an enjoyable exhibition that covers the art of Yosemite from native american basketry, to mid-19th century painters, to photography; highly recommended!