Fast Glass

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Zoom lenses have become increasingly popular over the years for a number of reasons, including convenience (less lost time swapping lenses and in turn less chance of getting dust on the camera sensor and/or missing the shot altogether), weight (one slightlier heavier zoom can replace two or three slightly lighter but collectively heavier lenses) and slimmer camera bags (have you flown with carry-on baggage lately?). 


But there are some pictures you can never capture with a zoom lens. And that's where fast fixed prime lenses come into the picture—figuratively and literally. 

Before the advent of sharp zoom lenses, most 35mm shooters headed out with a bag full of fixed focal length lenses (the earliest zooms were dogs in terms of sharpness). They almost always included a fast 50mm (usually f1.4), at least one wide-angle (usually a 28mm), a "portrait lens" (85 to 105mm) and something in the 180mm to 200mm range. If they owned one, they often packed something wider—20mm, 18mm or 15mm, and often something in the 300mm or longer range, because you never know...

With the exception of the 200mm-plus lenses, all of these prime lenses were fast, meaning f/1.4 to f/2.0, with the slower lenses falling into the f/2.5 to f/2.8 range, which was still fine if you were shooting Tri-X (ISO 400), but kind of dicey if you were shooting Kodachrome (ISO 64). Today, with the simplest DSLRs boasting 5-digit ISO ratings and in some cases, in-camera image stabilization, you don't necessarily need a fast lens to guarantee sharp results. Still, there are a number of important technical and aesthetic reasons why you should consider fast glass when populating the lens pouches in your camera bag.

Selective Focus

Selective focus, i.e., isolating your subject from the foreground and/or background, is a powerfully subtle way to guide the viewer's eyes to what's important in the frame. And this goes for stills as well as video. By shooting at the lens' widest aperture, you minimize the depth of field, which depending on the focal length of the lens and how close (or far) you are from your subject, reduces the foreground and background to various degrees of blurriness. Aside from eliminating visual distractions, this narrow range of focus better emulates the way we see.

Note: Our eyes only focus on about 0.5° of our total field of view at any given time. The illusion of "sharp all around" is a result of your brain's occipital lobe's ability to patch together all of the snapshots you gather at the rate of about 10 per second.


Fast maximum apertures allow you to guide the
viewer's eye by enabling selective focusing.

© Allan Weitz 2010. May not be reproduced without written permission.

Note: Selective focusing is easier to achieve when shooting with larger sensors, and while it is possible to achieve wonderful narrow-focusing effects with full-frame, APS-C and FourThirds format cameras, the effects are more dramatic and easier to achieve when shooting with larger-format camera sensors.

Fast Glass = Faster and  More Accurate Autofocusing and Metering

Lesser-known benefits of fast glass have to do with autofocusing and metering. In a nutshell, the faster the glass, the faster your lens's autofocusing system, which responds correspondingly faster in relation to the amount of light hitting the AF sensors. When recording autofocus response times, manufacturers base their results on how fast an f/1.4 lens responds on the camera, not the f/3.5-5.6 kit lens that ships with the camera.

And if you shoot with polarizing filters on a kit lens, be advised that most AF systems become increasingly sluggish once the effective f/stop drops below f/8, which is where a polarized kit lens resides wide open.

The same goes for metering. Light-sensitivity ratings are also established using faster (f/1.4) lenses, and just as your camera's autofocusing abilities slow down as the lens's maximum aperture diminishes, so does the metering accuracy.

Sharpness and  Minimum Focus

In terms of resolving power, zoom lenses have improved immensely over time. Still, prime, fixed focal length optics are sharper overall compared to their zoom counterparts. While many wider-aperture lenses cannot be described as tack sharp at their maximum apertures, what is in focus, and the way it plays off of the blurrier foreground and background details, more than makes up for their technical "shortcomings."

And for those who prefer to use polarizing filters when shooting outdoors, faster optics allow you to stop down two to three stops (the sharp, "sweet spot" for most lenses) and still maintain acceptably high shutter speeds without impacting on focus speed or metering accuracy. 

Lastly, most fixed focal length optics—fast or not so fast—tend to focus closer than their zoom counterparts, which explains why you'll often find a fixed 85mm, 135mm, 135mm or 180mm lens packed alongside a pricier 70-200mm zoom in many pro camera bags.                                         

Notes: Fast lenses 300mm and longer will be discussed in a separate upcoming Holiday Gift Guide. When considering any of the below-mentioned lenses, always check for possible compatibility conflicts between specific lenses and your particular camera model.


A Selection of Fast, Wide-Aperture, Fixed Focal Length Lenses by Manufacturer
  Format Min Focus Max Mag Ratio   Filter Size Weight

Full frame

APS-H

APS-C

 9.8" (0.25m)  1:6.25  77mm  1.4 lb (650 g)

Full frame

APS-H

APS-C

 9.6" (0.24m)  1:5.5  58mm  0.68 lb (308 g)

Full frame

APS-H

APS-C

 1' (0.3m)  1:5.5  72mm  1.28 lb (500 g)

Full frame

APS-H

APS-C

 1.5' (0.46m)  1:6.6  58mm  0.64 lb (290 g)
Canon EF 50/1.8 II

Full frame

APS-H

APS-C

1.5' (0.46m)  0.15x 52mm 0.29 lb (131.5g)

Full frame

APS-H

APS-C

 1.5' (0.46m)  1:9  72mm  1.2 lb (545 g)

Full frame

APS-H

APS-C

 3.2' (0.95m)  1:7  72mm  2.25 lb (102 g)

Full frame

APS-H

APS-C

 2.8' (0.85m)  1:7  58mm  14.9oz (422 g)

Full frame

APS-H

APS-C

 3' (0.91m)  1:7.3  58mm

 1.01lb (458 g)

Full frame

APS-H

APS-C

 3' (0.91m)  1:5.3  72mm  1.64 lb (744 g)
Canon EF 200/2L IS

Full frame

APS-H

APS-C

 4.9' (1.49m)  1:6.3  72mm  1.68 lb (762 g)
 

Full frame

APS-H

APS-C

 9.5" (0.24m)  1:5  58mm  1.16 lb (530 g)
  Full frame

APS-C

 11.8" (0.3m)  NA  72mm  1.87 lb (850 g)
  Full frame

APS-C

 3.28' (1m)  NA  72mm 21.16 oz (600g)
  Full frame

APS-C

 1.4' (0.44m)  1:2  67mm  24 oz (680 g)
 
(For Leica 'M' cameras only)
Full frame

APS-H

 3.3' (1.0m)  1:17  60mm  1.54 lb (700 g)
  Full frame

APS-C

 0.82' (0.25m)  0.179x  77mm  21.9 oz (620 g)
  Full frame

APS-C

 0.98' (0.299g)  0.2x  67mm  21.2 oz (600 g)
  APS-C  1' (3m)  0.16x  52mm  7oz (200 g)
 
(Manual Focus)
Full frame

APS-C

 1' (3m)  NA  52mm  14.6 oz (399 g)
 
(Manual focus)
Full frame

APS-C

 1.7' (0.5m)  NA  52mm  13.8 oz 390 g)
  Full frame

APS-C

 1.5' (0.45m)  0.15x  52mm  8.1 oz (230 g)
  Full frame

APS-C

 1.5' (0.45m)   1:6.8  58mm  9.9 oz (280 g)
  Full frame

APS-C

 3' (0.91m) 1:8.8  77mm  1.23 lb (558 g)
  Full frame

APS-C

 3' (0.91m) 1:6.6  62mm  13.4 oz (380 g)
Full frame

APS-C

 3' (0.91m)  1:7.7  72mm  1.4 lb (635 g)
  Full frame

APS-C

 4' (1.21m)  1:7.1  72mm  1.78 lb (807 g)
  Full frame

APS-C

 5' (1.52m)  1:6.6  72mm  1.7 lb (771 g)
  Full frame

APS-C

 6.2' (1.9m)  1:8.1

52mm

(Drop-in)

 6.4 lb (2900g)
  Full frame

APS-C

 6.2' (1.9m)  0.12x  

52mm

(Drop-in)

 6.45 lb (2930g)
 

FourThird

Micro FourThird

 1.1' (0.35m)  1:8  77mm  2 lb (915 g)
    FourThird

Micro FourThird

 4.6' (1.4m)  0.09x  77mm  58.2 oz (1650g)
   FourThird

Micro FourThird

 9.45" (0.24m)  1:2  52mm  10.6 oz (300 g)
Panasonic Lumix 20/1.7 Aspheric G   FourThird

Micro FourThird

 0.66' (0.2m)  0.13x  46mm  3.5 oz (100 g)
  FourThird

Micro FourThird

 15" (0.38m)  NA  62mm  1.1 lb (510 g)
 

FourThird

Micro FourThird

 7.09" (0.179m)  0.10x  46mm  1.94 oz (55 g)
Pentax smc FA 31/1.8 Limited  APS-C  1' (0.3m)  1:6.25  58mm  12.2 oz (345 g)
  APS-C   1.5' (0.45m)  1:8.4  49mm  5.5 oz (156 g)
   APS-C  2.3' (0.7m)  1:7  49mm  0.6 lb (272 g)
 

Sigma 20/1.8 EX ASPH DG DF RF

Full frame

APS-C

 7.9" (0.2m)  1:4  82mm  1.15 lb (522 g)
Sigma 24/1.8 EX ASPH DG DF Macro Full frame

APS-C

 7.1" (0.18m)  1:2.7  77mm  1.07 lb (17 oz)
 

APS-C

FourThird

Micro FourThird

 15.7" (0.4m)  1:10  62mm  15.1 oz (430 g)
Sigma 28/1.8 EX Aspherical DG DF Macro    Full frame

APS-C

 7.9" (0.2m) 1:2.9   77mm  1.06 lb (481 g)
Sigma 50/1.4 EX DG HSM Full frame

APS-C

 1.48" (0.45m)  1:7.4  77mm  1 lb (505 g)
  Full frame

APS-C

 33.5" (0.85m)  1:8.6  77mm  25.6 oz (725 g)

Sony 24/2 Distagon T*

(Carl Zeiss)

Full frame

APS-C

 7.5" (0.19m)  0.29x  72mm 19.58 oz  (555g)
Sony 35/1.4 G Full frame

APS-C

 1' (0.3m)  1:5  55mm  1.1 lb (510 g)
   APS-C  9.05" (0.23m)  0.25x  55mm  6 oz (170 g)
  Full frame

APS-C

 1.5' (0.45m)  1:6.7  55mm  8 oz (220 g)
Sony Planar T* 85/1.4 ZA Full frame

APS-C

 2.8' (0.85m)  1:7.6  72mm  1.2 lb (560 g)
  Full frame

APS-C

 2.5' (.72m)  1:4  77mm  2lb 3oz (985 g)