Loss of image quality after sensor cleaning?

Question

I use a 550D for photography. I got dust in my sensor few days ago while I was doing reverse macro and cleaned it from Canon Service Center. After cleaning I checked my sensor (taking picture of blue sky in smallest aperture) and It was okay. However, I'm afraid I'm seeing some other type of image quality degradation in my images. For example; ISO 1600 is producing more grainy images than before. Everything else is okay but I'm just afraid its producing more noises. Can it be an effect of bad sensor cleaning or its something in my head? I shoot RAW and I use 18-55mm lens. To be more subjective,

1. Is there any side affects of cleaning camera sensors that might affect image quality, particularly by increasing noise/grain?

2. How do I check whether my sensor is performing at its best or it has some problem?

Answer 1

It seems unlikely that a sensor cleaning would increase digital noise. (Not impossible, just unlikely.) It's more likely that you're just noticing the same amount of noise more now than you were before.

If some sort of fluid were used to clean the lens, it's possible that there could be a residue on the sensor. This would cause general or spotty unsharpness, might leave a color cast, etc., but shouldn't cause digital noise. It's also possible that your antialias filter is scratched - this would probably show up as a line of blurriness across the image. From what I understand, scratching your AA filter is pretty tough.

If you're still concerned, here's how I would double-check:

• Find a high-ISO photo that you took before the sensor cleaning. Preferably, this would be a photo from some place you have access to. (One from your own home would be perfect.)
• Set up your camera the exact same way this old photo was taken. Put your camera in manual exposure mode, and make sure these settings are all the same (They should be available from the EXIF info of the old photo):
  • Shutter speed
  • Aperture
  • ISO
  • Noise reduction
  • Image quality (raw vs JPEG high quality vs JPEG low quality.)
  • White balance/Color balance.
  • Any picture settings, HDR modes, etc.
• Go to where the photo was taken. Replicate the lighting that was used in the photo. If you can't get to where the original photo was taken, find a similarly-lit location. You may need to adjust shutter speed and aperture to get the same exposure as before.
• Take as similar of a photo as you can. Same place, same direction, same zoom. The exact subject of your old photo may not be present (people, etc.) but do the best you can.

Now that you've replicated the photo, load it into the same program you used before (Lightroom, iPhoto, whatever) and apply the same presets and adjustments. If you have the raw file for your old photo, re-process both without noise reduction.

Compare the new photo with the old one. Compare corresponding places from each photograph. Hopefully, they're the same; reassure yourself that the increase in noise is just in your mind. If they're different, call Canon, present the evidence you've just collected, and hopefully they'll fix or replace your camera for free. Then, of course, post the evidence here.

Answer 2

Depending on how you cleaned your sensor, you can actually set up semi-permanent static charges in the sensor's layers. This is well known by all who have taken apart web-cams to remove the IR filter. Immediately after their sensors are full of noise. But ... over a week's period of time, these static-charges will dissipate (usually). These induced static charges that remain are what are the basis behind all "electret" devices. Some electret designs have been known to retain their charges for hundreds of years.

To prevent this, avoid any of the cleaners that use the film or colloidal type of cleaning systems. Those where you have to pull away a sticky film from the sensor's surface. The two different materials being pulled away from each other can induce very large static charges in the underlying layers. Adhesive-tape companies go to great lengths to formulate their adhesives and substrates to try to prevent some of this, but it will always be an issue whenever two different materials are brushed against each other or pulled away from each other. Look up the Triboelectric-Series to see why this is so.

Answer 3

I've tested my 550D's sensor against my colleagues 550D and seems like its doing just fine. I did not find any previous high ISO reference shot from my camera to compare so I compared it against my colleagues, same settings, same subject. So, in fact, it was my mind playing with me, nothing else. "It's more likely that you're just noticing the same amount of noise more now than you were before." said by Evan Krall seems to be the perfect line, I selected his answer as the accepted one for that line. Though no one suggested to compare my camera with someones having the same model!

Thank you all for your help! I'm feeling somehow relieved now!