Is a 50-mm f/1.4 lens better than a 50-mm f/1.8 lens?

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March 2, 2011 at 10:27 am  •  Posted in Q&A by  •  1 Comment

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.

While it's not apparent in these photos, a 50-mm f/1.4 lens is larger/heavier than its more affordable f/1.8 counterpart; it may also be weatherproof (as the Nikon model is). On the other hand, the f/1.8 lens may have benefits in addition to lower price if it's a recently designed model, such as the very fast Silent Wave AF-S focus motor in the Nikon lens.

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.

The difference in shutter speed is not great at f/1.4 vs. f/1.8. This image, made at f/1.4 at ISO 100, required a shutter speed of 1/25 s. If I had used an f/1.8 lens instead, the shutter speed would have been around 1/15 s. but switching to ISO 200 would have allowed me to shoot at 1/30 s. © 2011 Peter K. Burian

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.

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One Comment

  1. Brad Calkins / March 8, 2011 at 10:11 pm / Reply

    Another point to consider is that the number of aperture blades is usually higher for the faster f/1.4 lens. The more blades, and the rounder they are, the smoother the background out of focus areas usually are. In the Canon line there is a f/1.2, f/1.4 and f/1.8 lens, and each has progressively ‘worse’ looking out of focus areas when stopped down. The faster the lens, the brighter the viewfinder as well.

    To me the biggest difference between the versions of this classic focal length is the physical quality of the lens, not the optical differences…

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