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I'm the owner of a new Canon 550D with a Canon 18-135mm IS lens.

While looking into the lens, I noticed what I think are two tiny dust particles (I would say smaller than 1mm) behind the first glass of the lens, that can be seen from the front and from the back, but I'm not sure if this can be noticed in the pictures. Given that I've paid some considerable money for this lens, is this something normal I can expect a new lens to have?

Apart from that (I think it might be unrelated) I also see two dots in the view finder. They are not related to this dust and, at least, I'm sure they are not visible in any pictures, but is this also something I can expect?

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While I wouldn't really worry too much about dust in the lens actually affecting image quality, I would say that is still not normal, and I would probably return a brand new lens if it came with any dust inside.

Here is a good example of how bad a lens can get before image quality suffers - Dirty Lens Article

As for the dust you see through the viewfinder, that could actually be in the viewfinder - which I wouldn't worry about, or it could be farther down the lightpath - such as on the actual image sensor. If you just bought a brand new camera and it had dust on the sensor right out of the box, I would guess that it wasn't brand new and someone took it for a test drive or two prior to you purchasing it. I would return for a new camera in that case.

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    \$\begingroup\$ Thanks for the article. Really interesting. Dust on your sensor though, that really sucks. Hence my comment on @Nick Miners answer. \$\endgroup\$
    – Vian Esterhuizen
    Jun 14, 2011 at 20:07
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    \$\begingroup\$ Great find on that article! I often have to talk my students into the idea that schmutz on the lens isn't nearly as detrimental as they may think... The article makes the point in a visual way that I can't be bothered to do myself. :-) Thanks! \$\endgroup\$
    – Jay Lance Photography
    Jun 14, 2011 at 20:39
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Zoom lenses are prone to 'inhale' dust, simply by the act of zooming. Dust is only an issue when it's close to the focal plane of the lens (i.e. the sensor), so the specks you can see on the front element are not going to affect your shots. It's entirely up to you whether you take it back - you don't need a reason to return an item (assuming you're in the UK) if it's in its original condition. Just take it back and buy another.

The dots you can see in the viewfinder are probably on the mirror or the upper surface - this would explain why they are not apparent in your pictures. It's generally good practice to keep your internals clean, so use an air blower to get rid of these.

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    \$\begingroup\$ Be careful with an air blower. I bent the curtains on me 30D with one. Had to send it for repairs. \$\endgroup\$
    – Vian Esterhuizen
    Jun 14, 2011 at 19:59
  • \$\begingroup\$ True - do use with care, but if you're cleaning the mirror or the viewfinder prism, with the mirror down, the shutter isn't exposed. \$\endgroup\$
    – user456
    Jun 14, 2011 at 20:01

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