Generally, if you have to choose between upgrading your camera body or your glass, upgrading your glass is the best choice.
So when you go looking for that next lens, how do you decide? Which lens should you focus (pun intended) on first?
Here are a few guidelines that might help you figure that out.
1. Determine what your budget is. If you’re short of funds, it might be better to save your pennies and wait until you can afford the lens you REALLY want. Rent or borrow until then.
2. If you have to choose between two average lenses and one really great lens, buy the really great lens every time. You can always zoom with your feet if you need different focal lengths. Rental to the rescue the rest of the time.
3. Fast glass, fast glass, fast glass. Buy the fastest glass you can possibly afford. You will NEVER be sorry you did. The good news here is that almost everyone who can afford a DSLR can afford a fast 50mm lens. You can buy a 50mm F/1.8 lens for under $125 in most places. That narrow depth of field you get with a fast lens, combined with improved low-light shooting capabilities and better sweet spots make the difference. A fast 50 is always a good investment.
4. Beware paying for a lens more than once. What do I mean? Well, let’s say you buy the 70-200 F/3.5 to f/5.6 variable aperture zoom because it’s cheap. Then you realize you would get better images out of a 70-200 fixed aperture F/4. So you sell the variable aperture zoom at a loss and step up to the fixed aperture F/4. You have certainly improved your glass. But then you realize you need the best 70-200 you can get for shooting indoors in low-light situations and you make the final leap to the 70-200- F/2.8 fixed aperture zoom. You sell the F/4 at a loss and buy the F/2.8. By the time you lost money selling the first two lenses to help pay for the one you really wanted in the first place you paid too much. Just save up for the lens you really want and buy that. In the mean time you can rent.
5. When buying used, make sure you don’t buy a lens with dust or mold inside. Preferably, only buy refurbed/used lenses. These are typically guaranteed by the manufacturer or the retailer and offer the best value.
6. When possible, stick with the manufacturer’s brand of lens. If you shoot Nikon, buy Nikon glass. If you shoot Canon, buy Canon glass. This doesn’t mean that some of the third-party lens manufacturers don’t make great lenses. They do. And I have owned or do own several. But I only buy the third-party stuff when there’s nothing in the focal range from the manufacturer. Nikon doesn’t make a 100-300 mm zoom so I bought the Sigma 100-300 F/4 zoom and love it. Likewise, Nikon doesn’t make a 300-800 mm zoom, so I bought the Sigma 300-800 F/5.6 and love it. If Nikon made lenses in the focal range I’d probably buy them instead, if for no other reason than quality control. The third-party lenses tend to suffer from poor quality control more often than the mainstream manufacturer’s lenses do. In other words, you’re more likely to get a “bad copy” of a third-party lens than you are a lens from your camera manufacturer.
7. Look for stabilization. If you can buy a fast lens with or without stabilization, i.e., VR on a Nikon, OM on a Sigma or IS on a Canon, save up for the lens that is stabilized. You’ll get sharper handheld images and you’ll appreciate the results.