Bob Buchanan
Well-known member
? ? Have just had a bad bout with sensor dust on my Rebel XT DSLR--and thought I would pass along info on the experience (or rather, "bad" experience ). I had read an article on this some time ago, but had since forgotten about it. I have been shooting w/my XT for several months now, and did not notice the problem until several weeks ago. Unfortunately, the job I was doing was construction progress -- so the shots in question cannot be done over. Thank goodness for digital darkroom. Also, the shots I was doing were at small aperture settings (F20.0 to F40), so the wider DOF make the dust spots stand out more.
Most of my work prior to that has foliage or other mixed background. However, when looking closely at a clear blue sky above a horizon, I noticed numerous fuzzy little thingy's that reminded me of a chemistry class years ago. At first I thought I had dust on my lens -- but tests showed that it was dust on the CMOS sensor (CCD sensors have the same problem). The booklet w/the camera (as all DSLR's probably do) had a process to clean it. I decided to first take the camera back to the Pro shop of my purchase to learn more about the problem. Was glad I did. Here's some of what I discovered:
o The dust is not on the sensor, but rather on the glass cover over the sensor. The sensor itself is further protected by the shutter and the mirror in its normal down position.
o The dust entry happens during lens changing. Actually, the dust doesn't go right to the sensor, but rather builds up on and around the SLR mirror. The sensor builds an electric charge over time. So when a pic is shot, the mirror goes up, the shutter opens, and the sensor's charge sucks the dust in. Some pros tell me that the pumping of a long lens creates a vacuum that will then suck dust into the housing when that lens is removed.
o The technician at my camera store cleaned the sensor for me. He suggested a hand bulb type blower and suggested "never" using a gas powered blower. He first removed the lens and blew dust from the mirror and housing around the mirror. Was amazed at how much was in there. He then raised the mirror and cleaned behind it. He then put the camera into sensor cleaning mode and cleaned the sensor itself. He then took a test shot and put the results into a computer graphics package -- and the dust appeared to be gone. Unfortunately it wasn't with my follow up tests so I returned to the shop.
o This time the authorized service person cleaned the sensor. He said that there was still tons of dust even after the initial cleaning. His cleaning was more thorough -- and now my test show no dust.
Anyway, I am now very conscious of this problem and am very careful when changing lens. They suggested I always hold the camera in a down position and keep my lenses covered when not in use. They also suggested a general bulb cleaning of the mirror and housing after a day of shooting if the lenses are changed -- or at least after several sessions. They did not charge me for the pro cleaning, but mentioned if my camera was not so new, the normal charge for a sensor cleaning is $75.00. Ouch!!
Here's a couple of articles I found that are pretty detailed and cover most of the points I mention here.
http://thomashawk.com/2006/04/10-tips-for-new-digital-slr.html
http://www.photosafaris.com/Articles/CleaningTheSensor.asp
Those with fixed lens cameras do not have this problem as the sensor is always protected from dust.?
Most of my work prior to that has foliage or other mixed background. However, when looking closely at a clear blue sky above a horizon, I noticed numerous fuzzy little thingy's that reminded me of a chemistry class years ago. At first I thought I had dust on my lens -- but tests showed that it was dust on the CMOS sensor (CCD sensors have the same problem). The booklet w/the camera (as all DSLR's probably do) had a process to clean it. I decided to first take the camera back to the Pro shop of my purchase to learn more about the problem. Was glad I did. Here's some of what I discovered:
o The dust is not on the sensor, but rather on the glass cover over the sensor. The sensor itself is further protected by the shutter and the mirror in its normal down position.
o The dust entry happens during lens changing. Actually, the dust doesn't go right to the sensor, but rather builds up on and around the SLR mirror. The sensor builds an electric charge over time. So when a pic is shot, the mirror goes up, the shutter opens, and the sensor's charge sucks the dust in. Some pros tell me that the pumping of a long lens creates a vacuum that will then suck dust into the housing when that lens is removed.
o The technician at my camera store cleaned the sensor for me. He suggested a hand bulb type blower and suggested "never" using a gas powered blower. He first removed the lens and blew dust from the mirror and housing around the mirror. Was amazed at how much was in there. He then raised the mirror and cleaned behind it. He then put the camera into sensor cleaning mode and cleaned the sensor itself. He then took a test shot and put the results into a computer graphics package -- and the dust appeared to be gone. Unfortunately it wasn't with my follow up tests so I returned to the shop.
o This time the authorized service person cleaned the sensor. He said that there was still tons of dust even after the initial cleaning. His cleaning was more thorough -- and now my test show no dust.
Anyway, I am now very conscious of this problem and am very careful when changing lens. They suggested I always hold the camera in a down position and keep my lenses covered when not in use. They also suggested a general bulb cleaning of the mirror and housing after a day of shooting if the lenses are changed -- or at least after several sessions. They did not charge me for the pro cleaning, but mentioned if my camera was not so new, the normal charge for a sensor cleaning is $75.00. Ouch!!
Here's a couple of articles I found that are pretty detailed and cover most of the points I mention here.
http://thomashawk.com/2006/04/10-tips-for-new-digital-slr.html
http://www.photosafaris.com/Articles/CleaningTheSensor.asp
Those with fixed lens cameras do not have this problem as the sensor is always protected from dust.?