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Message: <blockquote data-quote="Julian" data-source="post: 1424277" data-attributes="member: 21416">Hi TerryTamron 90 Di is superb and great value for money. Every bit as good in terms of optical quality as the Canon. I have both so can compare. It is not internal focusing though so the lens grows in length as you focus closer as opposed to the canon which stays the same. Having said that, it isn't a problem and is quick to lock on. One advantage over the internal focusers (I think and hope I am right in saying this-but it's late, gone midnight and I am very tired so I might be talking rubbish) is that the focal length is unchanging ie, constant. Whilst the canon says 100mm, it actually varies slightly depending on distance. With the Tamron, it's 90mm through and through. This may or may not matter to you, I suspect not. What you want is a good quality reasonably priced lens. I would add that you should alwasy try a product before you buy. There is sometimes variation in quality, even between identical models.Best of luckJulian</blockquote>