Camera viewfinders are great place for dirt, dust and lint to collect. Because they are recessed, never have a cover or cap on them like the front of your lens, and, if you carry your camera around your neck or over your shoulder, are often in contact with your shirt or jacket, it is no wonder they are often the dirtiest part of any camera. Fortunately, cleaning them is very quick and easy.
Start with the cotton swab that has been moistened with a small amount of lens cleaner. Gently clean the external side of the viewfinder, starting in the corners and moving to the centre.
Using the lens cloth, start again in the corners and follow the same path around the viewfinder ending in the middle to pick up any dirt the swab did not, and removing any moisture that may remain from the swab.
Use the small camel hair brush to get right into the corners of the viewfinder to remove any leftover debris.
Finish the cleaning process by using the lens brush with the air bulb to remove any small amount of lint or hairs that may have been left behind by the cloth or brush. Start in the corners and follow the same path as you did with the cotton swab. Be sure to use the air bulb often during this step.
Sometimes dust will find a way to get inside the camera. If you are using a single lens reflex (SLR) camera--either digital or film--you can remove the lens and clean the mirror, and--by turning the camera upside down and looking into the cavity--you will see the focusing screen that can also collect dust and debris. Follow the same steps for cleaning both, but use extra care when cleaning the focusing screen as it can become damaged.