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What is a “fast” lens?

2009-07-01 - Send Feedback
Related: howto, shutter

What is a "fast" lens anyway?

Applied to a lens, the term "fast" refers to faster shutter speeds made possible by the superior light gathering power of a lens.

A fast lens is always larger heavier and more expensive than a slower one. For example, a 50mm f/1.2 lens might cost $1600 compared to $300 for a 50mm f/1.4 lens and $100 for a 50/1.8.

Each f-stop represents a full shutter speed. So an f/1.4 lens allow one faster shutter speed than an f/2 lens, and two faster shutter speeds than an f/2.8 lens. That's a very big deal at dusk, or indoors.

Most consumer zooms are in the f/3.5 - f/5.6 range, meaning that they lose 2-3 shutter speeds, a huge difference leading to blurred images when the light levels drop (which requires a lower shutter speed).

Examples

An aperture which is 1.4 times the previous one is half as bright eg f/2 is half as bright as f/1.4. Faster apertures (e.g. f/1.4 or f/1.2 or even f/0.95) are far more challenging to design and build to achieve high quality.

Focal length range
(for 35mm format)
Max Aperture
12mm - 21mm f/1.4, f/2
22mm - 35mm f/1.4, f/2
50m f/0.95, f/1, f/1.2, f/1.4
85mm f/1.2, f/1.4
90mm f/2
100mm, 135mm f/1.8, f/2
180mm, 200mm f/2, f/2.8
300mm f/2, f/2.8
400mm f/2.8, f/4
500mm f/4
800mm f/5.6

Top recommendations for fast lenses

Lenses I've used and/or own, and can heartily recommend.

Click on links to each lens for reviews.

Zeiss for Nikon or Canon

View prices for Nikon or for Canon

Canon

View prices.

Canon's f/1.2 lenses are unique. Nikon does not offer f/1.2 lenses as of 2010.

Nikon

View prices.

Leica

View prices.

 

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