This is the third part of the lens purchasing guide will cover a wide range of lenses, from high end crop sensor lenses, to lenses designed for full frame DSLRs. The first part of the guide will focus on lenses for crop sensor lenses and finish with lenses for full frame cameras.
Professional Grade Lens or Crop Sensor Cameras:When it comes to professional grade lenses for crop sensor cameras there are not a lot of choices. Canon and Nikon both have 17-55mm F2.8 crop lenses that are well made and provide a normal focal range with the build quality and optics to make them match their $1000+ price point. Aside from these two lenses there are no first party choices for crop sensor users who want professional quality lenses. That means if you want professional quality lenses for your crop sensor camera, and those lenses do not appeal to you, you'll either have to look to third party lens makers or at full frame lenses, neither of which is a bad thing.
This second part of the guide will be useful for people with full frame camera, or for people who are looking to upgrade to a full frame camera in the near future, but currently have crop sensor cameras. First I'll discuss zoom lenses. If you include third party choices you will have a few lenses in each category to consider, between wide angel, standard, and telephoto.
For wide angel lenses, you need to look for a lens that is best able to capture what you like to photograph. If you shoot landscapes or architecture try to find a lens that gives you a wide enough angel so that you don't have to take several images and stitch them together. Although stitching images together will get the job done, it is also a time consuming task. Canon offers two wide angel lenses, the 17-40mm F4L USM and 16-35mm F2.8L II USM, while Nikon has the 16-35mm F4G VR and 14-24mm F2.8G. All wide angel lenses have distortion on the wide end, but the more distortion it has the more post processing you will have to do, and the more corner image quality you will loose as you reduce the distortion. Wide angel lenses will capture a lot of depth of field wide open, which means you do not have to stop them down as much as a telephoto lens to get more of the frame in focus, so look for a lens that is sharp wide open (smallest F number), or at least close to it. For ultra wide angel lenses the third party manufactures haven't made very many attempts to enter in the full frame market, as all third party wide angel lenses are for crop sensor cameras at this time.
When it comes to standard zoom lenses you have a lot of choices, one or two from the first party camera makers, and an additional 3-5 from third party lens makers. Canon and Nikon both make 24-70mm F2.8 lenses, which are excellent in terms of build and image quality. Those two lenses are some of the best lenses in terms of image quality on the market today. Sigma has two have 24-70mm F2.8 lenses, one is an older lower cost design with a older auto focus motor (doesn't have one in the Nikon version) and a newer HSM version with a more powerful up to date auto focus motor, but it is more expensive. Tamron also has a lens in this category, the 28-75mm F2.8. These third party lenses do offer better image quality than the kit lenses for full frame cameras, but they lack the build quality and price of the first party lenses. The first party lenses do have an edge in image quality, sometimes by a wide margin, but you have to decide if those differences are worth around $800 in price differences.
When it comes down to choosing which of these lenses is right for you, there are a few factors that come into play. First of all your budget, this is going to be the driving factor behind your choice, but your budget needs to be set based on your usage. If you shoot professionally, then picking the first party lenses is your best option without a doubt. On the other hand if you either do not make money from your photography, or only make profit off your photography on the side, then the third party lens options may be the right choice. Standard zooms allow you to get close to your subject, or into short telephoto range on full frame cameras. They also are wide enough on full frame cameras to take landscape or architectural photos, although you do need to watch out for distortion on the wide end of these lenses. Common uses also include portrait photography.
Next we look at the telephoto lenses that most professionals carry, 70-200mm lenses. If you shoot with Canon cameras then you have a number of Canon lenses to look at, because there are four 70-200mm lenses in that lineup, with two F4 versions, one with IS and one without, and two F2.8 versions, one with and one without IS. Nikon on the other hand only offers one 70-200mm F2.8 VR lens, and then there are the third party options from Tamron and several from Sigma. The first party F2.8 lenses are the best in their class, and the price reflects that with Nikon and Canon's lenses costing over $2000 Cdn. In the case of 70-200mm lenses you start to see why the first party lenses are more expensive, for example the Tamron lens has a lot of plastic in its construction, and auto focus for the lenses may not work with some budget DSLRs, from manufactures like Nikon. 70-200mm lenses are appealing because the allow you to either step back and give your subject more room, or for reach in situations where you cannot get closer. The F2.8 models also give you the option of attaching teleconverters, which are useful if you need even more reach, and since they are fast the use of 2x TCs is possible to double the focal length.
There are many other lenses that will appeal to professional users and advanced amateurs, but the lenses listed are the most common focal ranges that people are interested in. Many professional users will be interested in super telephoto lenses, and primes, but I will talk about such lenses in another guide, perhaps.