It's a Floor Wax and a Dessert Topping!
Dust spots can create serious problems for photographers. What method you use to solve those problems though depends on where that dust is at. And choosing the wrong solution can cause serious damage.
The most obvious place for dust to alight is on the front of your lens. That surface has to be exposed in order for light to get through the lens in order to form an image. Some people will tell you that you can protect the front surface of your lens by using a clear or UV filter to protect it. But this is only partially true. For one thing, what protects the front surface of that filter? Even if you stack multiple filters atop each other, each one to protect the one underneath, the one on the very top will still be exposed. Plain and simple, dust, fingerprints and other contaminants can find their way to the topmost surface unless you are careful. Adding "protective" filters doesn't solve the problem, it only moves it to a new surface. Sooner or later, you are going to have to clean that surface.
There are all sorts of fluids available on the market that purport to be lens cleaners. Some are better than others, and some cost more than others. Don't make the mistake though of thinking that you can use Windex or a similar glass cleaner. Your lens surface may be glass, but it also has several coatings that can easily be damaged by the ammonia in general purpose glass cleaners. Unless I have stubborn spots, my preferred solution is to simply breathe hard on the surface of the lens to dampen it. Unless I've been eating a strange diet, the moisture in my breath is clean, safe, and certainly convenient.
Don't ignore the cloth you wipe your lens surface with either. A dirty T-shirt could scratch the lens surface. Cheap lens cleaning tissues are also a poor choice. This is not a place to save money. My personal preference is either a PEC-Pad from Photographic Solutions, or a good, clean microfiber cloth. It's best to put a few drops on the cloth and then wipe then lens. Applying the solution directly to the lens could result in it running down to an edge and getting inside the lens.
Often, salesmen in camera stores will try to sell you lens cleaner with every purchase, much the same way that McDonalds wants to sell you French fries with every order so they can make more money from you. Given that it will only take a couple drops to clean a lens, a small bottle of the good stuff will last a long time. Resist the temptation to buy more on impulse or by sales pressure.
This brings me to the other major area subject to dust spots: your camera sensor.
As archaic as film photography seems by today's standards, film did have one advantage over digital. Every image you shot was on a fresh frame of film, and every 36 exposures, you put in a completely new roll. Little, if anything, carried forward from one image to the next. The film started in a sealed canister and ended up back inside that canister after the roll was finished. Dust had little chance of getting directly on a frame, and even if it did, it was even less likely to be on the next. With a digital camera though, every image you ever take will be exposed on the same media. If dust gets on the CMOS sensor inside your camera, it will be there on every image you take from then on.
One of the advantages of an SLR camera is that it uses interchangeable lenses. But every time you change lenses, you risk getting dust on your sensor. No, with a bit of care, it's not a big risk, but it can't be ignored completely. Sooner or later, dust will get inside your camera. Even then, it may not land on your sensor, but it could.
Most camera manufacturers recommend that you send your camera back to them to clean the sensor. But that's inconvenient, and probably expensive. To avoid this hassle, many photographers eventually try to clean their sensor themselves. Doing so isn't hard either, but as with many things, you need to know what you are doing first, and you need to have the proper tools. There are several different approaches to cleaning a sensor, but the most commonly used one is called the "wet method," and has a lot of similarities to using a cleaning solution to clean a lens surface. But while both involve wetting and wiping the surface, it's here that the similarities end.
Just as you wouldn't want to use Windex to clean your camera lens so as not to damage its surface, you shouldn't use lens cleaner fluid to clean your sensor since it's even more delicate than your lens is. The standard liquid to clean your sensor is Eclipse by Photographic Solutions, the same people who make PEC-Pads mentioned previously. There may be other options out there, but I wouldn't want to risk trying them. My advice is to stick with Eclipse. This is what most camera makers use if you do send them your camera to have the sensor cleaned. The standard tool to use with Eclipse is called a Sensor Swab.
The history of Eclipse can be somewhat confusing and is worth spending a bit of time here to clarify. Once upon a time (circa late 2004), Photographic Solutions introduced Eclipse cleaning fluid. The product was basically just ultra-purified methanol, an alcohol that evaporates quickly, and leaves no residue. The formulation was developed in collaboration with "major camera manufacturers" as a way for their technicians to clean sensors. By 2006 though, Sony and then Nikon the year after began using a coating known as Indium Tin Oxide (ITO) on their sensors. Sensors always have had a glass surface over top of the electronics, but they originally were basically just plain glass. This new ITO coating was completely transparent and started to be used as it made dust less likely to stick. When this came about, Sony tested Eclipse fluid on their new sensor design and decided that, while it seemed to still be safe, they would feel more comfortable with a somewhat less "aggressive" cleaner. Thus was born "Eclipse 2" (or E2) fluid, for use on cameras with ITO coating on their sensor. E2 consisted of ethanol together with some methanol as well as a bit of isopropanol alcohol. Both original Eclipse and E2 contained very little water. Over time, virtually all sensor designs started featuring ITO or similar coatings, and thus E2 became the dominant standard. It was always safe to use the gentler E2, but the use of original Eclipse on an ITO sensor could be risky.
When Cannon released the EOS 5D though, things got more complicated. Oddly, even though the 5D had ITO coatings, sporadic reports of E2 damage to 5D sensors caused Photographic Solutions to reformulate things once again. In 2009, Photographic Solutions introduced a new version of Eclipse (original name) and discontinued Eclipse 2. This new version is even more pure than the original and has been deemed safe on all sensors. That makes things simpler for everybody. Even though this change happened some years ago now, I have periodically heard from users who were confused when they went to buy more E2 fluid only to find it no longer existed.
Next, we move up the timeline to 2015 when Sony introduced the Sony a7ii DSLR. Apparently, the coatings used on its sensor are indeed safe for cleaning with Eclipse when used correctly, but excess pressure could result in damage. Instead, PhotoSol has been recommending the use of their latest sensor cleaning product, Aeroclipse for these new Sony mirrorless sensors (presumably including the new a9). Aeroclipse was originally designed for travel and is non-flammable. Having less methanol though, it is also gentler on sensors than even the reformulated Eclipse. So basically, we're back to having two versions of Eclipse (or Aeroclipse), for use depending on the sensor you have.
By the way, sometimes users wonder whether they can use Eclipse to clean their lenses so they only need one fluid. The short answer is, yes, they can, but Eclipse evaporates so quickly that it's hard to clean an entire lens element before its gone. So practically speaking, you are probably better off with separate solutions rather than trying to use one for cleaning everything.
(With thanks and appreciation to Chevy Chase, Gilda Radner, Dan Aykroyd and the original Saturday Night Live for the title of this week's article.)