Your choice of camera lens brand goes hand in hand with your choice of Digital SLR brand. This is because a Digital SLR will have a lens mount that restricts the lenses it is compatible with. For example if you own a Canon Digital SLR it will have a Canon lens mount and you will not be able to use lenses made by Sony or Nikon with it.
All the leading Digital SLR brands (Canon, Nikon, Sony and Pentax) produce their own set of lenses to go with their camera bodies. Each brand produces a wide range of lenses covering all your requirements from wide angle to super telephoto. Therefore when it comes to the flexibility of the lenses you are not really restricted when deciding which Digital SLR brand to go with.
Be aware that with leading brands now offering Compact System Cameras as well as Digital SLRs brands can have more than one lens mount. For example if you buy a Sony Digital SLR it will have a Sony A mount. If you buy a Sony Compact System Camera it will have a Sony E mount. Although you can buy lens adapters to make most Digital SLR lenses compatible with Compact System Cameras, lenses made for Compact System Cameras cannot be used with Digital SLRs.
This is a subjective question. The most popular brands are Canon and Nikkor (Nikon). Both of these brands consistently produce high quality camera lenses.
A lot of people prefer Canon cameras and lenses. A lot of people prefer Nikon cameras and lenses. This tells me there is not a great deal of difference when it comes to the quality on offer from the leading brands. Therefore when it comes to selecting the brand you would like to buy, take a look at what's on offer and decide which one suits you best.
Whether you buy a Digital SLR and lenses from Canon, Nikon, Sony or Pentax you will have a camera capable of taking excellent pictures. How you use your camera is far more important than the brand you buy.
You will find each brand sells lenses with similar or identical focal lengths, but at different price points. For example Nikon and Canon often have three different levels of lens for the same focal length. As you may expect these are starter lenses, mid range lenses and professional lenses.
As well as the components being of a higher quality with the more expensive lenses you may notice other differences too. For example one of the key factors in determining the cost of the lens is the size of the aperture. So if you are looking for a lens with an extra wide aperture, be prepared to pay more for the lens.
Camera Lens Introduction
Buying Your First Lens
Camera Lens Types
Camera Lens Brands
Buying Second Hand Lenses
Digital SLR Crop Factor
Caring For Your Camera Lens
Common Lens Faults
Camera Lens FAQs
As well as being able to buy "own brands" such as a Canon lens to go with a Canon Digital SLR you can also buy lenses made by third parties.
Leading third party brands are Sigma, Voigtländer,Tamron and Tokina. The main advantage of buying a third party lens is that they tend to be cheaper than "own brand" lenses.
The big question is how close they come in quality when compared to "own brand lenses". In my view they quality gap has narrowed significantly in recent years, especially from Sigma and Voigtländer. Therefore if your budget is a bit tight it is well worth considering a lens made by a third party.
When buying a third party lens it is normally clear what lens mount they are compatible with, but extra care should be taken to avoid expensive mistakes. For example a Sigma lens with a Canon lens mount will not work with a Nikon Digital SLR.
There are other third party brands available, but personally I would be wary of them unless you are looking for a cheap lens to have a bit of fun with.
All brands sell a mix of lenses for Full Frame Digital SLRs and Digital SLRs with a crop factor. (Follow this link to find out more about crop factors: Digital SLR Crop Factors). The important point to know is that you can use lenses made for Full Frame Digital SLRs on a Digital SLR with a crop factor, but you cannot use a lens made for a Digital SLR with a crop factor on a Full Frame Digital SLR.