brian_keyashian Posted July 12, 2006 Share Posted July 12, 2006 Hey Everyone, I bought a Rebel XT and a sigma 17-70 f2.8-4.5 lens. I like the lens a lotexcept for one small problem. There is a dark spot on all the images takenalthough its only noticable against lighter backgrounds. It occurs accross theentire focal range and I am not using any filters. I also don't think it is aproblem with the camera. The dark spot does not appear on pictures taken usingmy canon 50mm f1.8 lens. I've cleaned the lens and both the front and rear lenslook clean. Does anyone have any idea what it is or how to fix it? I posted a full size image to my portfolio. Thanks,Brian Link to comment Share on other sites More sharing options...
PuppyDigs Posted July 12, 2006 Share Posted July 12, 2006 A small percentage of XTs have a sensor defect causing it to record small segments of far infared light, oft appearing as an apparition. This is the realm of earth bound spirits and creatures trapped between here and the afterlife. By facing east, blessing your XT thrice and immediately stroking your sensor with a magical brush you may render these phantoms invisible. Sometimes the light’s all shining on me. Other times I can barely see. - Robert Hunter Link to comment Share on other sites More sharing options...
bobatkins Posted July 12, 2006 Share Posted July 12, 2006 Does it get worse when you stop the lens down. Is it worse at f22 than at f2.8? <p> If so, see <a href="http://www.bobatkins.com/photography/digital/sensor_cleaning_ii.html"> This Page </a> Link to comment Share on other sites More sharing options...
brian_keyashian Posted July 12, 2006 Author Share Posted July 12, 2006 I haven't noticed any difference in the spot with regards to aperture or focal setting. However, I haven't specifically tested different apertures. I will tomorrow when its sunny out. Link to comment Share on other sites More sharing options...
dcheung Posted July 12, 2006 Share Posted July 12, 2006 That looks like sensor dust. You don't see it with the 50 1.8 because the apertuer is so wide that such that the depth of field is too narrow to notice the dust on the sensor. If you use the 50 1.8, try the Av setting and change the aperture value to f16 or higher and you will notice the dark spot. In fact, the higher the f-number, the more the dark spot will look like a black dot signifying a particle of dust on the sensor. Link to comment Share on other sites More sharing options...
brian_keyashian Posted July 12, 2006 Author Share Posted July 12, 2006 Thanks for all of the help! haha...now if I can only figure out how I managed to get dust on the sensor the very first time I used the camera. Link to comment Share on other sites More sharing options...
PuppyDigs Posted July 12, 2006 Share Posted July 12, 2006 You probably didn't. That's likely genuine Canon authorized and issued factory dust. Sometimes the light’s all shining on me. Other times I can barely see. - Robert Hunter Link to comment Share on other sites More sharing options...
zacker Posted July 12, 2006 Share Posted July 12, 2006 lol,lol,lol.. so much for the whole "Clean Room" theory!-zacker- Link to comment Share on other sites More sharing options...
jon_austin Posted July 12, 2006 Share Posted July 12, 2006 What ever gave you the impression that Canon assembles their dSLRs in a clean room environment? Link to comment Share on other sites More sharing options...
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