Mystery White Spots with the CP950 or CP990.
I have seen several examples of "Mystery White Spots" on CP950 and CP990 photos. These white spots appear when you use the flash, and the background is dark. Below is an example of the most common problem.
Dust in the air
Here the spots are caused by dust in the air, close to the lens, brilliantly illuminated by the flash. The tip off is that the spots will not be in the same position on subsequent photos, even if the camera is held motionless with fixed focus on a tripod. This rules out internal reflections in the lens (lens flare) or dirt in the lens system. The case with the CP950 (and presumably also the CP900) is exactly the same as previously reported here for the PDR-M1 camera (See this link), so I will not repeat the entire argument here, but go and read if you would like the details..
As an example, I took the CP950 outdoors at night, and pointed the camera up into the black sky. I shook out a dust rag near the camera (cough) and took a flash shot with the CP950. Here is the result...
Notice how the dust "spots" prefer the left side of the field, which is where the flash is. In this case, the camera was focused at infinity, and the larger (more out of focus) sport are due to dust bits closer to the lens. The closer dust spots are also closer to the flash so they receive more light, and closer to the lens so they are brighter (inverse square law). Imagine these superimposed on your picture; you might think that there was something wrong with your camera. The CP950/990 does not seem as succeptable to the spots as some cameras such as the PDR-M1.
You are most likely to see these spots in a dusty environment, where the air is being stirred up a lot, such as a large room filled with dancers, and probably not as many as are shown above. You are more likely to notice the spots if you try to streach the flash out too far; reaching out too far into a large room, which causes a dark background making the spots more visible.
There is nothing wrong with your camera if you see these spots and they are not in the same position all the time.
Other types of bright "spots"
Dust in the air illuminated by the flash isn't the only way to get bright "spots" on your picutres. Instead of dust, a fine misty rain will have the same effect, and can be even more pronounced due to total internal reflection of the light from the flash back to the camera. Actual rain will also generate "spots" if you flash it, but you probably should not have your camera out! Pro photographers know all about dust and rain being illuminated by the flash and how to work around it. (use a slave flash farther from the lens)
Drop of water on the lens
Another way to see "spots" to have a drop of water on the lens. In this case, you don't need the flash to generate the spot, buy you do need an external light such as a lamp in the distance. What happens is the water drop acts like a little lens and refracts some light from the light into the lens; the same sort of thing that happens in a rainbow. In this case, the spots on your picture will be larger than the typical dust spot, and they will have a halo of color around them (depends on the color of the light being refracted) It is sort of analogous to the spots that you see when you are sitting in a dark car on a rainy night looking out at lights through the windshield.
You can also get this effect when using the flash from some synthetic fibers that have a circular cross-section or fibers that have a metal glitter added or are contaminated with reflective particles.
Normal reflections of the flash
You will also see "spots" formed by reflection of the flash off all sorts of objects. Drops of water on swimmers, sharp metal objects or corners (such as a doorknob or the corner of a metal window blind), reflective surfaces (such as a knife or fork), polished plastic toys, moist eyes,lips and teeth; all can reflect the flash and give a very small bright highlight that looks like a "spot".
In the case of all of the bright spots, they are most visible against a dark background; an underlit room, a piece of dark clothing.
You may also see lens flare, although it seems to be pretty rare in the 950 lens system. This is caused by a bright external light source, usually the smaller the better, at just the right angle outside the field of view. The image of the source is reflected off one or more of the internal lens surfaces to form a spot or dot on your image. Sometimes you will even get a "train" of lens flares leading away from the light source. That is why they coat lenses with anti-reflection coatings. The thing about lens flare, is that if you take several pictures without moving the camera, and without focusing (that can move the internal elements), the flare will always be in the same place. If you move the camera, the lens flare will change. The trail of "flares" usually points right to the light souce (such as a streetlight) in your picture. It is possible to get a flare from a light source that is out of the actual picture.
Hot Pixels, don't be fooled
With all of the current hype about "hot pixels", especially in the 990, it is important not to confuse these flash reflections with real stuck pixels on the CCD. Here is how to distinguish real hot pixels from all of the effects above.
* Real hot pixels are always in the same place. Exactly. Use your photo program to make a note of the exact positions.
* Real hot pixels do not require the flash to be on. If your problem goes away when you turn off the flash...
* Real hot pixels are only one pixel wide. (At higher compression settings there may be some bleed over though. Also, sometimes you can get a cluster of hot pixels).
* Look at the distribution of the spots in your shots. Are they just over fabric? Over the wet swimmers? Over people's wet eyes or lips?
* Real hot pixels are generaly more evident with longer exposures. If you have not noticed the problem before on longer shots, the spots that you are seeing on a flash shot now are probably not hot pixels
Large Faint Dark spots.
These appear as a dark, almost circular spot against a bright background such as the blue sky. Their size can change depending on the zoom and focus level, but they will be located in the same position on two subsequent shots at the same zoom and focus.. They do not need the flash. They are almost always dirt or dust somewhere in the optical system, on the lens surface, somewhere in the lens train, or on the CCD itself. Unless it is on the outside of the lens, you don't have any chance of cleaning it off yourself and will have to send it back to Nikon for cleaning. (Hint. I have HEARD that people have cleaned the 950/990 by themselves. This would void your warranty, of course, and I can't recommend it. I sent my 950 in to have Nikon clean it).
Spots due to dirt in the lens system are large and diffuse, and their size changes as you zoom and focus the camera. They may be invisible at some zoom or focus settings, and can usually only be seen on a uniform background. Spots due to dirt on the CCD are smaller and darker. They do not change size with focus or zoom (since they are sitting near or on the CCD and always subtend the same angle as seen from the CCD).
Dirt in my 950 optical system caused the dark spot to the upper left of the balloon. If you look closely, you can see several. I'll probably have to send my 950 in to be cleaned. (I did sent it in, and Nikon cleaned this dirt out nicely. The repair bill said "Clean Iris Assembly").
If you look closely, you can see several spots.