There's nothing worse than thinking you've gotten the shot only to find out when you get home hours, days, or weeks later to process the shots that you have dust bunnies all over the frame. It's a lot like getting your negatives home and discovering that the processing lab scratched your negs or used tainted chemicals.
Lightroom and Photoshop both have very useful tools for getting rid of them in post-processing, especially on blue sky or other pretty even colors, but if the dust was over a part of the image that has intricate texture it can be tricky. And it still takes time to manually go in and remove them, especially if you've been shooting for timelapse. Try removing dust bunnies from 999 images at once on a part of the frame that's changing.
It's definitely one of those times that prevention is much better than the cure. The time that your camera is most vulnerable to dust is when you're changing lenses (and it follows, of course, that if you never change lenses you're less likely to run into the problem.) Film SLR's have an extra barrier between the film and the entryway for dust in addition to the mirror, but that layer isn't there for a DSLRs where, apart from the mirror, the sensor is basically exposed. Modern zoom lenses are getting pretty good about being flexible enough to leave on for much of the day, but there are still times when you might want to change lenses. I'll often have two cameras on me at any given time with different lenses on, but there are times that just cry out for that super fast prime lens for a specific shot--but those lenses are usually less flexible. Which is all to say, there are often compelling reasons to change lenses on the go.
Ideally, you'd change lenses in a dust-free, still environment. That might work in a studio; on the road, though, is a different matter. But there are some things you can do to help minimize the problem. They won't eliminate the problem, but they can help.
- Start with a clean sensor. It might seem obvious, but checking and cleaning your camera after each shoot is a good habit to get into. When I'm on the road, I try to make it a nightly chore back at the hotel room along with downloading and backing up my shots from the day's shooting.
- Get out of the breeze. If possible, try to change the lens away from breezes and preferably in an area with as little dust as possible. Indoors is often better than outdoors.
- Start with a clean lens. Be sure that the camera end of your lens is clean and free of dust. It's an easy thing to overlook when you're focusing more on the camera body.
- Power the camera off. When digital cameras are powered on, the sensor maintains a small static charge. That static charge that goes through the sensor attracts dust. And the last thing you need here is to turn your sensor into a dust magnet.
- Make it quick. Try to keep to a minimum the time that your camera body doesn't have a lens on it. The longer it's exposed, the more chance there is for dust to enter. I like to have the new lens ready to go before taking the old lens off the camera body.
- Regular preventive cleaning. A dust-blower is a very useful addition to your bag, but I find that using it while out and about can often make the dust problem worse. So I'll often try to use it back at the hotel at the end of the day rather than trying to use it on the go. Nevertheless, I always try to have one with me, and sometimes it's the best option to use it while out and about.
- Regular thorough cleaning. Periodically give the sensor a more thorough clean. There are a number of options available to do it yourself. It's careful business; here's a great article that goes through some of the best options. If you've got a real problem, send it in for a professional cleaning.
- Emergency tip. Sometimes there's just nothing you can do because conditions are just bad or it it would take too long and you'd miss the shot. If you're really, really stuck with dust on your sensor and no chance in the short term to clean it, you can try using a larger aperture (eg. f/4 or f/2.8). That might help minimize the problem on the image. Smaller apertures (eg. f/22 or f/11) tend to be more prone because they have a much greater depth of field. It's not at all foolproof, but it can help.
With a little luck, making these a matter of habit should help stop those pesky dust bunnies from breeding like, well, you know.