Dead pixel(s) or ?

Photographing an air display on Sunday every shot on the 1D had a

black spot almost central. Tried to clean the sensor tonight but

the blemish though clearly visible does not seem to be on the

surface of the glass but rather behind - and yet it seems too big to

be a single "dead pixel" - anyone have any ideas ? Two crops from

samples can be seen at www.sportfile.co.uk/diagnose . Tried both

blower and eclipse fluid cleaning methods. Thanks in advance for any

enlightenment.

It appears to be a large chunk of dirt.

 

If it's really behind the anti-aliasing/ir-blocking filter, then a trip back to Canon is in order. How anything could get in there, I've no idea about.

 

It's not dead pixels in the normal sense of that term, though I suppose if you've hit the sensor with a high energy laser blast, it could be...

Holy crap that thing is huge! Certainly not dead pixels in the usual sense. Could the low pass filter on the front have suffered damage from any sort of impact? I can't see how anything would have gotten under it, and the cleaning would have at least helped the problem if it were surface dirt. Either impact damage or intense light source (i.e. laser) would be my only thoughts.

Excuse me for suggesting the obvious, but any chance it's on (or in) the lens? (Did you try swapping lenses to verify?)

Derek;

 

It looks too symmetrical to be a dust bunny, but I suppose it's possible. To check for dust, try shooting a blank wall at F4 and then again at F22 but keep the overall exposure constant. If it's dust, then at F4 it will seem to defocus and partially disappear. It it's damaged sensor, then it will be a constant blemish. For your sake I hope it's just a dirty sensor. Some crud can be very sticky, such as tree sap, tiny bugs and pollen grains.

 

Good luck, ...Dave

A very decent-sized chunk of crud sitting right on the sensor - be real careful cleaning, or you'll make it worse. Read up on the various schools of sensor cleaning (on this forum!) before you attempt it.

Thanks guys - yes the appearance changes at different apertures (the two on line samples show it more clearly)so that's a comfort - I can see the thing on/in the sensor so no it's not lens dust - I'll have another look with the jeweller's eyeglass - eclipse cleaner made not an iota of difference - perhaps backtracking through shots until the occurrence might explain something - the camera is usually at 2.8 shooting sport and the blemish may well have been there a while.

With binocular magnifier it's obviously on the surface and casts a shadow - so far so very good. But if eclipse fluid doesn't shift it what else is worth trying?

Desperation drove me to try the Scotch tape trick - the blemish moved to the edge but is still there albeit diminished - first cursory check shows no damage - fingers crossed.. Why the hell this thing moves but won't be removed beats me - even fired an anti static gun in there but it made no difference - weird. First fears of sensor failure unfounded - but weird.

Looking at your last photo you can see quite a lot of smaller dust marks so cleaning the whole sensor is required. I have just returned from a trip to find that most of my photos are covered by dust/debris marks and I have had to carry out a major PS action to clear them. It took about 5 goes with a damp lens tissue (Bob Atkins proceedure) to finaly get the dirt under control as the blower method did not have any effect. Good luck with your cleaning.