I have two zooms with a maximum aperture of f/4.5-5.6 so I’m planning to buy a “fast” 50-mm lens for low light photography without a tripod. What is the difference (besides price!) between a 50 mm f/1.4 and the 50 mm f/1.8? It seems like such a minimal difference but the f/1.4 lens costs about $300 more. Do you think I should buy the more expensive model? —Marian Ormond
You’re right Marion; an aperture of f/1.4 does not sound much wider than f/1.8. In fact, it’s less than one stop so the shutter speed in a dark location will not be substantially faster. And yes, the f/1.4 lens (of any brand) is significantly greater in size, weight and price. That’s partly because the wider aperture requires a barrel of wider diameter and larger pieces of optical glass. Note too that the lens elements must be more effective at correcting optical aberrations which are more problematic at f/1.4 than at f/1.8. All of this drives up the manufacturing cost.
Check out the two 50-mm lenses and you’ll also note that the f/1.4 model is far more rugged, with tank-like construction. Some, like the Nikon 50 mm f/1.4G are also weather-resistant, useful when shooting in a dust storm or during inclement weather. The superior construction makes sense, because a 50-mm f/1.4 lens is usually bought by professional photographers or by very serious photo enthusiasts. Both expect the very best in build quality.
Even with high-grade optical elements, it’s very difficult to make a lens that will provide superb image quality at f/1.4. Often, the 50-mm f/1.8 model will provide comparable quality at f/1.8. Hence, you should be perfectly happy with the less expensive lens unless you’re certain that you need the slightly wider aperture and more rugged construction. Before making a final decision, read test reports at www.slrgear.com on the two specific lenses that you are considering. You’ll probably be pleasantly surprised to find that the f/1.8 model provides decent image quality at f/1.8 and excellent from f/2.8 to f/11.