Noise at low ISO. Dirty sensor?

<p>Hello,</p>

<p>I've recently noticed that the photos I've been taking (using a Canon EOS 7D) have more noise than before at low ISO. Can anyone please tell me if this can be a result of a dirty sensor? I have had my camera for 2 years and haven't had the sensor cleaned yet, so it most probably needs to go through a round of cleaning.</p>

<p>Below is a link to a sample picture that I took a few weeks ago. This photo (2396 x 1598) has been cropped out of a bigger photo (5184 x 3456). I have not resized the image, just tweaked the exposure in Adobe Lightroom. The photo was taken on a bright day. Image info:</p>

<p>Camera: Canon EOS 7D, Lens: Canon EF 100-400mm IS, F-stop: F/8, ISO: 200, Focal length: 400mm, Shutter speed: 1/1000 s (hand-held).</p>

<p><a href="http://img593.imageshack.us/img593/3964/mg4799.jpg">http://img593.imageshack.us/img593/3964/mg4799.jpg</a></p>

<p>If you take a look at this image it looks too noisy for a photo taken at ISO 200. Can that noise be due to dust on the camera's sensor?</p>

<p>Many thanks,</p>

<p>Tausif</p>

<p> </p>

<p>When a picture is under exposed, noise will be visible even at low ISO. That is the nature of most sensors.</p>

<p>Most of your picture is bright blue sky, where perhaps most likely the exposure metering was evaluated from. The bird flies in fast, and perhaps your metering was not done on the bird at all. What metering mode you used? <br>

In cases like this, shooting bright sky plus something on it, you need to make sure that you compensate exposure, so the subject is exposed correctly. Use spot metering on the bird - (if you can catch it), or rather compensate exposure a lot to predict this case of lighting.</p>

<p>You " <em>just tweaked the exposure in Adobe Lightroom" </em>- so it is hard to tell how this looked originally unchanged from the camera. Perhaps you brighten up the picture ? to bring some details and the noise with it?, from perhaps strongly underexposed picture of the central subject.</p>

<p>What is interesting that <em>"I have had my camera for 2 years" </em>- and rather than perfect your techique, you say your pictures deteriorate ?</p>

<p>Perhaps there is no dust on the camera sensor. Cleaning could possibly help, if done right, but you need to focus on your shooting technique, and know how...</p>

<p>Dust usually shows up at narrow apertures and most peple set the aperture to F22 when checking for dust. Dust is almost never visible in a photo when the aperture is set wide open. I frequently take a picture of the sky at F22 to check for dust which typically appears as black dots. I don't see any dust in your picture but I would recommend you take a picture at F22 to be sure. To me it just looks like sensor noise, not dust.</p>

<p>Yes, the subject does look underexposed, although the sky, too, appears to be noisy.</p>

<p>In any case, dust on the sensor has nothing to do with the excessive noise in the image.</p>

<p>Thanks Frank, Steven, and Mark. I really appreciate that you took your time to answer my post. And yes, this picture was a little under exposed and I had to fix that in Lightroom.</p>

<p>You're right, I do need to improve my technique. I'm never satisfied with my photos. I need to shoot more often. This was the first time I went to take photos of birds (with a rented lens). The metering mode that I used was partial metering. I'll try spot metering next time I go to photograph birds, thanks for the tip.</p>

<p>Such noise as is present is caused by under-exposure; but I would not call it seriously objectionable. Spot metering may not work with fast-flying birds. Manual settings should be better after a couple of test shots.</p>

<p>You could try what I do when shooting aircraft against a bright sky, which is to use manual mode and lock in your exposure from something on the ground, then leave it alone when you shoot your subject against the bright sky. The sky might blow out but at least your subject will be well exposed.</p>

<p>Thanks for the suggestions Mukul and Chris. I will try exposure lock. I had read about it, but never tried it while shooting. I do always shoot in manual mode. When it comes to actual shooting I always forget about techniques that I read :-).</p>

<p>Do you have highlight tone priority on? Having it on automatically increases the noise output at any ISO.</p>

<p>Thanks for the response Edo. I have highlight tone priority disabled.</p>