How to Prevent Sensor Dust Problems

Digital sensors are like little static electricity machines that attract minute and sometimes grain-sized dust particles of dust. You can “spot” the particles out later (which record on the image as black dots and streaks) using cloning tools and various healing brushes and blur tools, but having to spot images in this way is painstaking and not a good use of time, especially when the problem can be eliminated or diminished with a bit of care.

Manufacturers have not denied the problem and many cameras now incorporate dust “cleaning” systems that turn on every time you start up the camera. Generally these “shake” the sensor in the hopes of vibrating the dust off; sometimes this works OK and other times you might have to use more drastic measures. The best bet is to try to prevent dust from catching on the sensor in the first place.

All told, dust is pernicious and can work its way inside the camera in more ways than one: here’s some advice about keeping it to a minimum.

1) Always store the camera in a case or bag. It might look handsome on a bookcase or shelf but you are needlessly exposing it to ambient dust.

2) Never change a lens with the camera turned on. Having a charge across the sensor plane when it is exposed will act as a dust magnet.

3) If possible, change lenses inside a vehicle or changing bag, especially if there is any wind. This is when many dust problems occur. Turning your back on the wind and shielding the camera when changing lenses might help, although doing so when shielded by a coat is better.

4) If shopping for a camera, get one with a dust reduction (shake) system and that bills itself as having extra seals to prevent dust. These “dust-proof’ and “weather proof cameras” are worth it. And if you take lots of outdoor nature shots, especially in dusty environments, it’s a good idea to get well-sealed lenses as well.

This photo made with a loaner camera looks "innocent" of dust 

...but close inspection of the sky area reveals a dust nightmare. 

As an exercise I wouldn't want to repeat I enlarged the image to 100% on the monitor and worked with the clone tool and healing brush to eliminate all the lines and particles. Needless to say I won't be loaning from that service again. If you find similar problems send your camera to a reliable service center or the manufacturer and get that dust removed.

Checking for Dust

If you look through the viewfinder and see dust you might not have dust on the sensor—it might be on the lens itself or in the DSLR viewfinder prism or mirror. Check the lens. If the prism has the dust it can be bothersome, but that dust will not show up on your pictures. If the mirror has dust use a gentle cloth, gently, or compressed air.

Inspection

The only way to know if you have a sensor dust problem is to take a picture and inspect it by using the magnifying tool in your computer software—it may not how up on your small playback LCD. Download and enlarge your images at 100% (though that might be too late for a day’s shoot.) Another good test is to shoot a blank white sheet of paper, download the image, and move it around it to check the entire enlarged frame—this will make the dust spots quite visible.

What If You Have Dust?

If you do have dust on the sensor try restarting the camera (if it has a dust reducing system) a few times to see if you can have the system “shake” it away for you. If your camera has a “clean now”  feature you can use this instead of restarting it.

You can try cleaning the sensor yourself with commercially available kits, although I would caution you to be very, very careful if you go this route, as damage can easily occur. The best route for really bothersome dust (but isn’t it all) is to send the body back to the manufacturer or a certified repair shop for cleaning: this is the safest route. Many such services will do an overall check of the camera, including "pixel mapping" (identifying "dead" pixels) as part of an overall CLA (clean, lube and adjust).

Spotting with Dust Delete Programs

What if you have a precious and special image that simply can’t be reshot and you want to clean it of dust? Some manufacturers offer “dust delete” software for their camera cameras.

Here’s a typical dust delete procedure.

1) First, find where the dust delete setup is in your camera menu.

 2) Activate it and the self-cleaning procedure will start.

 3) Photograph, and fill the frame with a solid white object, like a sheet of copy paper. This photograph will not be saved to a card. The menu screen will confirm that is has “captured” the dust “data.” You then load and use the camera manufacturer software to automatically spot out the specks in your image. 

Note that this does not remove the dust but ID's the offensive dust and samples neighboring pixels to "spot" it out. You may have to go in and do additional spotting later. Yes, you can save one or a series of images this way, but don't go into the field without having the camera serviced.

Yes, you can spot and blur and the healing brush in software like Photoshop, but this can be painstaking for really dusty images. If you’ve ever tried to do that, you know what I mean. So, the best protection is to prevent dust from getting on the sensor in the first place, and checking periodically if the dust buildup is getting really, well, dusty.

 

How to Prevent Memory Card Corruption

There’s nothing more frustrating than going into the field and later discovering that your memory card did not “take” your take. 

While there are software programs that can help recover files that do not read when you try to download (google: recover damaged image files), or even files that do not show up in playback on your camera right after you shoot, the best bet is to prevent conditions that can cause corruption in the first place. 

Here' are two images "recovered" from a corrupted card. This showed up as one file after I ran the card through a recovery software program. Interesting, I suppose, but certainly not what I had in mind.

Here are some quick tips for preventing memory card corruption:

1)   Don’t carry memory cards loose in your pocket or camera bag. Dust, dirt, and lint can “clog” the card’s pins and interface areas, and cards can be bent or otherwise damaged by other items in your bag. Use a dedicated card carrier available as an inexpensive accessory that has slots that hold cards separate from one another.

2)   Inspect the card for damage. The chief problem is bent pins, sometimes caused by forcing the card the wrong way into the slot in the camera. Look for insertion guides and if it does not slide in smoothly, back it out carefully. If you do have bent pins the card may be irreparably damaged. My experience is that trying to fix it yourself is not very rewarding. Bent pins make it just as difficult to read from a card reader. If you must, try to fix the bent pins with a needle nose plier or tweezer. My best advice: Toss it, but only after you try to retrieve images later.

3)   Make a few shots prior to going out in the field. Check that the test shots show up in playback. If they don’t, you are playing with fire.

4)   Always swap and load memory cards by first turning off the camera to avoid static discharge.

5)   If you have more than one camera, dedicate the card to one camera and do not swap it to your other camera. When you first use a new card in your camera be sure to use the format function; dedicating a card for use in that camera will remove any possibility of a mismatch. While this is not always a big problem, different cameras may have unique file structures. The formatting command is usually found in your setup menu. (Note: if you are using an older card for a new camera always check for images first, as formatting will erase those older images.)

6)   If you are working in the field and nothing comes up on playback, first try turning off the camera and reloading the card. However, it is better to remove the card and replace it with another and deal with the problem card later.

7)   If you do get corrupted or unreadable files, you can try out downloadable file recovery software. My experience with some of these programs is mixed, but it could just work for you—it’s worth a try!

Film Grain and Image Aesthetics

Grain is present in all film, but as grain size relates directly to film speed, the rule is: when going for the finest grain choose the slowest film speed possible and, conversely, when looking to enhance grain choose a high-speed film. The "possible" in the low grain rule takes lighting conditions and whether or not you're working with a tripod into consideration.

This grainy rendition was created by exposing Tri-X 400 at ISO1600 and "push-processing" (extending development time) the film using D-76 at full strength (no dilution). This resulted in a dense negative that was then printed using a #3 grade paper. The background was extensively "burned in" during printing. Torrey Pines Beach, 1988, Tri-X 400 exposed and push processed to ISO1600.

        

Today there are both “normal” (random grain placement) and T (for tabular) grain films. Tabular means the grains are “cloned” to be consistent throughout the emulsion. While this may seem academic, T grain films have a “smoother” look overall when printed, while “normal” grain films have a more “photographic” look associated with them. For example, you can get Tri-X 400 or T-Max 400, the latter having grain structure that is somewhat smaller and more light efficient than the grains found in the older emulsion formulations. While these T-grain films do offer finer grain in equivalent speeds when compared to the older formulations, the faster T-grain films are still grainier than slower T-grain films.

Some photographers do everything possible to reduce grain in their images--they shoot with the slowest speed films; they keep developing times to a minimum; they enlarge on low-contrast papers; and use so-called "fine-grain" developers. (Use of these developers usually means the loss of a portion of the speed at which you rate the film.)

Other photographers go the opposite route, and do whatever possible to enhance grain for graphic effects. You can boost grain by shooting with the fastest film available; by overdeveloping film (within reason); and by printing on high-contrast papers (or multi-contrast papers that allow you to change the grade by filtering the enlarger light: for example, a magenta filter for higher contrast.). Another way to enhance or smooth grain is to choose between a condenser or "diffusion" enlarger, the latter yielding a smoother grain look. As the visual effect of grain is linked to the degree of enlargement (magnification), some photographers either enlarge their prints to huge sizes, or take small portions of the frame and enlarge that section (cropping) to increase the image magnification even further.

Smooth grain images result from using a moderate speed film or inherently fine-grain film like T-Max, developing for lessened time, being careful not to overexpose, and printing on a #2 or lower grain using a diffusion head enlarger. This scene was photographed in 1989 on T-Max 400 with exposure biased towards the highlights. The film was developed in T-Max developer at 30 seconds less than the recommended developing time with 1-minute agitation intervals.

Most photographers do not get obsessed with grain, as long as it doesn't get in the way of visual communication. There is a school, however, that expresses the opinion that grain is an inherent characteristic of the "photographic" image, and that emphasizing grain, or not being too concerned when grain becomes evident, stamps an image as eminently "photographic." Grain is also used by photographers to add a nostalgic, mysterious or even ominous note to an image.

The best way to discover ways to enhance or diminish grain is to test various film/exposure/development combinations. For example, shoot a few rolls of Tri-X and do a “ringaround” of exposure, changing ISO and even exposure compensation as you shoot. (In other words, make images in low and moderate contrast light, both of the same scene, and bracket both ISO and settings, say by one to two stops of exposure and setting ISO at 200, 400 and 800 ISO.) Do this with a few rolls and develop one in a fine grain developer (which, as mentioned will have you rating Tri-X 400 at maybe 200 or 320) and one in a more active developer such as D-76, diluting 1:1 and 1:2 with water.

After development make contact sheets and then pick a few images that are over, under and well exposed. Enlarge a few frames to a minimum of 8x10", and use a loupe to help “predict” the resultant look of the grain on future frames shot at the same settings.

Once you have done this, make notes for your future field work. These notes will become your “grain” diary and will help you make choices for various subjects, scenes, and settings, and create just the right degree of expressive grain for your work. That way you will “stamp” or embed each roll of film, making the frame an “original” that truly records your mood and aesthetics of the moment you snapped the shutter.

Note: Pushing (through development) and rating ISO 400 film at ISO 1000 and above will certainly yield more grain. You can also punch up grain by developing any film in a highly-active developer, such as a paper print developer, for about 1.5 minutes. This will yield a very dense, but printable, negative that has "popping" grain.

Backlight: Exposure, Options and Techniques

The sun was striking these still-green leaves on a bough backed by brilliant color and stark trunks. The difference between the bough and background was about 1.5EV, but reading right off the bough made the colors in the background to go darker, which created a strong play of brightness and color.

As the term implies, backlight is a strong light behind your subject as it faces the camera. In some cases it can cause exposure problems, but it is also one of the most beautiful light sources for translucent subjects. Think of stained glass windows in a church. They are rather dark and dull when the sky is overcast, but when the light comes through them they are the most glorious window treatments of all.

Backlight is inherently contrasty, meaning that there will be a considerable difference in exposure between parts of the subject and the light behind it. In some instances this means that parts of your subject will either sit in silhouette (having form but no detail within the form) or be considerably underexposed. The key to backlighting is to exploit this contrast, to use the shadows it “throws” toward the camera as part of the composition. You do this by biasing exposure toward the brighter light. The usual solution to getting detail in a subject that is backlit is to use flash to “fill” the foreground subject with light, but that defeats the purpose and dramatic potential of this kind of lighting.

Tools and techniques: spot metering mode, exposure compensation, autoexposure lock.

The bright light here is supplemented by reflections off the pond, which provides a natural fill light for the darker parts of the scene. Nonetheless a spot meter reading of f/16 at 1/250 second at ISO 200 was made directly off the bright yellow leaves on the left side of the frame.

Perhaps the most colorful season in which to exploit backlighting is fall, when brilliant color displays combine with low angle light. The key to exposing this type of lighting is to avoid bringing shadow areas into consideration and read from the backlit leaves themselves. This is easily done by using spot metering mode and locking exposure on the brilliant light of the leaves. In most cases this will be the proper exposure, but in some instances you might want to use a + exposure compensation to add some brightness to other parts of the scene. This rarely goes above +0.5EV. Once you attain the exposure and review it to make sure it does the job, lock it, or switch to manual mode to maintain the exposure as you work in the area.

If you are shooting in the shade with a bright sky behind the main subject you can either crop out the sky and not worry about contrast, or expose for the main subject and deal with the bright backlight later in processing. These formations sat in deep shade but I wanted the sky for relief of the forms at the top of the frame. I used CWA to make the exposure, locking it on the formation itself, then recomposed. Later in post I selected the sky, which was blank in the recording, and added a very light blue color wash.

There may be times when working with backlight that the sun is higher in the sky and/or cannot be absorbed by a dense background.  It is essential to then make sure you block the sun from both the image and from exposure consideration. I often do this by finding a shadow area cast by the foreground subject and stand within it to make the picture, or at least position myself so that I block the sun with a branch, rock or other obstruction. Failure to do this will result in flare and an exposure that is thrown off by the strong presence of a direct light source. In addition, it is never a good idea to look through the finder directly at the sun. In this shots I used a branch to black the sun and took my spot reading from the leaves of the center tree.