Here’s the problem: sometimes a weird, rectanglish purplish bright light shows up. It can be seen on these pictures:
(Beware; the pictures are 1.6 megabytes each)
Strangely enough, it doesn’t show up if the picture is taken with flash. Also, it doesn’t show up on the viewfinder until -after- the picture is taken. Apparently, there’s nothing wrong with the sensor array, but I wouldn’t know what else might have caused it. Does anyone know what it might be?
Well, clearly the central area of the CCD is totally saturated - the purple surround represents overflow of charge from the saturated area. As for why, I’m stumped. Initially I thought you might have something in front of the lens, if the viewfinder is separate from the lens, but (a) that would only show bright white if the flash was used and (b) the “object” is too central and doesn’t extend to the edge of the frame in any direction.
This could be a number of things, but the purple looks like the kind of discoloration you get when CCDs overheat. To me this looks like as if somebody shined a laser pointer into the camera and took a long exposure shot, allowing the spot where the laser point is hitting the CCD to overheat – although that’s obviously not what’s happening. Try experimenting to see if this is related to exposure time – take pictures in very bright light and very dark conditions and see when this happens and when this doesn’t.
This could also be some sort of weird sensor blooming although those are usually vertical or horizontal lines rather than blobs in the middle. Basically you’ll probably need more data points of when this happens and when this doesn’t to determine what’s wrong. Ambient temperature, humidity, light, exposure time, aperture (or ISO setting), type of lighting (does it happen with sunlight?), battery level, etc.
The fact that it doesn’t show up on the screen until after the picture is taken is not surprising. The camera is running in completely different mode until you take the shot, after which it briefly displays a scaled down copy of the image you took (which has the blob). After this the camera reverts back to live view settings on the CCD (it skips lines to increase framerate and has to use digital amplification to prevent exposure longer than 1/10th to 1/15th of a second – which is typically the lowest acceptable live view framerate)
Do you mean to say the blob persists during live view AFTER the shot is taken? If so for how long (a couple of frames? seconds? minutes?)
It’s chromatic abberation in your lens, which is pretty common especially in cameras with a big optical zoom ratio. The lens isn’t sufficiently corrected with multiple glass types. You can make it go away if you use a straw or light yellow filter. I think your flash doesn’t put out enough purple light to notice this. Everything light in all your pictures has this around it, but most things aren’t bright enough to make their purple noticeable.
Chromatic aberration causes purple fringing around high-contrast areas, but it doesn’t cause a huge white area to blot out most of the picture! The purple fringing is an artifact of the whatever-it-is that is screwing up the image.
Chromatic aberration just doesn’t come and go – if it’s there it’s there, and if it’s only visible sometimes it’s probably subtle and requires certain lighting conditions and long exposure to become evident.
Chromatic aberration DOES come and go, in the practical sense that you don’t see the effect if you filter out the wavelengths that make it noticeable or if those wavelengths aren’t abundant enough to appear over other regions of the image. In a literal sense, if chromatic aberration is a design flaw in a lens, the lens is still flawed when for other reasons the aberration isn’t noceable, like when the camera’s sitting in your closet - so in a literal sense it doesn’t come and go, but the OP’s complaint can be fixed with a filter.
Mangetout, I think the huge white oblong is the image of a lamp and belongs in the photo. The chromatic abberation is just the purple fringe spilling out of it.
“In photography, and particularly in digital photography, purple fringing is the term for an out-of-focus purple ghost image on a photograph. Images taken with high-contrast boundary areas involving daylight or gas discharge lamps are particularly susceptible, since chromatic aberration is worst for the shortest wavelengths that a camera is sensitive to (violet and/or ultra-violet light).”
If it’s a lamp, yeah. However, it doesn’t look like a lamp to me at all. It looks like a big hole in the picture, and, as often as I’ve had overexposed lamps in my photos, I’ve never seen anyone make anything that looks like this.
edit: In fact, I would stake my professional reputation on it that it’s not a lamp.
There is definitely CA on the blotch in the center, but I really don’t think that’s an overexposed lamp since there’s no lamp. Take a look at the flash photo, they are the same scene. That space is occupied by a sock, some carpet, and a bookcase or something wood.
It’s a flaw in the CCD or the electronics of the camera, and I doubt there’s any fix since it’s practically a disposable camera. If it were an entry level name brand camera I’d send it in for warranty repair, but on this camera I’d just toss the whole thing.
Compare Flash and No Flash. They’re the same scene. Where’s the lamp?
I just showed the picture to our image quality expert and got a " :dubious: ", and he concurred with my sensor is overheating the middle theory as the most likely explanation. Try upping the ISO setting (if you can) and see if the occurrence rate goes down
>There is definitely CA on the blotch in the center, but I really don’t think that’s an overexposed lamp since there’s no lamp.
Uh… gee… this is weird. There sure isn’t.
Somehow I saw this picture as already right side up (not sideways) and showing the headlight of a car. Bizarre.
So, I don’t know what is causing the white rectangle. If it’s really some source of light, the purple fringing looks like CA, but the purple fringing is a secondary issue to the white rectangle.
FWIW I think CCD overloads should be smeared in a vertical or horizontal direction because of the way the chip marches the image off its surface and over the A/D converter, so the rectangle should be from something else. And it doesn’t make sense that an innocuous middle region would be way, way overloaded without any consequence to the outer regions. So I’m wondering how this brilliant stray light got there.
I think the OP is saying the whole thing - the oblong, the purple haze - is an artefact of some malfunction. If the OP is taking an overexposed, too-close-to-focus picture of an oblong lamp, then the whole question of why it’s happening is secondary to the question “why are you doing that?”.
Even if this were the case, I wouldn’t say the purple glow would be chromatic aberration - it would more likely be some kind of halation=type scattering inside the sensor assembly, or just plain overload or something.
I’m sure the oblong is the thing that’s not meant to be there, that we’re meant to be diagnosing.
My best guess would be some kind of fault in the flash circuitry, coincidentally located in just the right (wrong) place to be directly affecting the CCD assembly. Maybe a faulty capacitor leaking charge into the back of the CCD (IOW when the flash is actually used, there’s no charge to leak, and the effect doesn’t occur).
