Photographers | Should You Spend Good Money On Fast Glass?

A colorful view, over a pagoda rooftop, down onto a tranquil pool fed by a small waterfall near Huangshan, China.

The discussion as to whether or not to purchase fast glass is an age old one for photographers. I often get the question, "Should I buy a fixed/prime lens?" Here's what I think.

Photography And Lenses | What Is Fast Glass All About?

Just as the camera's Shutter Speed determines the amount of time, usually in fractions of a second, that light is allowed to reach the sensor or film it is the Aperture that determines how much light the lens allows through. And in photography speak an italics f is used to define a particular aperture (e.g., f/4).

A steam filled pipe, helping to generate geothermal power, crosses a green, verdant landscape in Iceland. This image was made on a Sony A7R II Camera with a Sony/Zeiss 24-70mm f/4 lens at f/11

Apertures | Comparing Numbers To Openings In The Lens

An aperture of, for example, f/22 is referred to as a narrow aperture as it's relatively small and lets very little light through. Conversely f2 is a relatively wide aperture that lets significantly more light through onto the digital sensor or film.

The vast majority of lenses available today offer the ability to set one of numerous apertures from, for example, f/4 to f/22. Basically, the term fast glass relates to the ability of the lens to let more light through and onto the sensor or film than would be the case with a lens with a narrower maximum aperture.

So a lens with a maximum aperture of f/2 provides the ability to let two stops (i.e., four times) more light through than would be the case with a lens with a maximum aperture of f/4. Both lenses have an aperture of f/4, but only the f/2 lens has the ability to open the aperture wider than f/4. In this case as wide as f/2.

An intimate moment between two horses at dusk near the town of Chewton in Central Victoria, Australia

Photographers | Do You Really Need Fast Glass?   

You buy a fast lens for its ability to produce exceptionally shallow DOF and to be able to work, hand-held, under low light conditions.

The above image of the two horses in rural Australia was made with a Canon 85 mm f/1.2 lens at an aperture of f/2. That's a physically wide aperture which, in addition to the short subject-to-camera distance, produced the very shallow depth of field that contributes to the uniqueness of the image.

What's more faster lenses are generally more expensive which means they're generally of a higher quality. And by that I mean they promise better image quality and are more physically robust.

The best quality fixed lenses will likely be made of glass and metal, rather than plastic and plastic, and may incorporate weather and/or dust seals.

Intricately carved statues, under late afternoon light, frame an entrance to the spectacular Notre Dame Cathedral in Paris, France. I made this image at an aperture of f/11 as that's where I found the lens in question to be at its most critically sharp. 

Zoom Lenses Deliver Great Convenience, But Also Compromise

Zoom lenses are, in effect, a variety of different focal lengths within the one lens. They incorporate a number of individual glass elements, some of which move, in relation to each other, as the lens focal length is altered by zooming in or out.

These factors tend to reduce the amount of light getting through to the sensor. As a result zoom lenses with maximum apertures wider than f/4 are expensive, heavy and considered to of professional quality. This is particularly true for ultra wide-angle and the most powerful telephoto (as in telescopic) zoom lenses.

A lovely, delicate black and white portrait of a young woman by window light in Melbourne, Australia. An aperture of f/4 was sufficient to produce a lovely, shallow depth of field given the relatively close camera-to-subject distance.

Prime Or Fixed Lenses | What's Best For You?

The same is not true for fixed or prime lenses. Depending on the focal length it's possible to acquire a fixed lens with a maximum aperture of f/1.4 for a number of wide-angle, standard and short telephoto lenses. As a way of explanation f/1.4 allows 8 times more light to reach the sensor than f/4.

Making images at an aperture of f/1.4 has the affect of increasing the camera's shutter speed from, for example, ⅛ second up to 1/60 second, minimizing the chance of blur resulting from camera and/or subject movement.

As explained previously, an aperture of f/1.4 also has the capacity of producing a substantially shallower depth of field (DOF) than would be the case with the same image made at an aperture of f/4. Under the right circumstances really, really beautiful images can result.

How To Improve Framing And Composition In Your Photography

There's no doubt that a zoom lens offers a great deal of flexibility when it comes to framing an image. If your subject is too far away simply zoom in to allow them to fill more of the frame. Likewise zooming out will allow you to fit more of the surrounding scene into the frame.

The problem is that zoom effects more than just the size of the subject within the frame. Zooming changes focal length which alters perspective and the angle of view rendered within the frame. As a consequence the relationship between the subject and its surrounds is altered, and not always for the best.

A gravestone adorned with a Christian cross and framed by a rainbow at the Lake Bolac Cemetery in Victoria, Australia.

Move To Make Really Amazing Photos

Please remember that photography is a physical endeavor. One advantage for the serious photographer is that, where and when you have the ability to do so, moving closer, further away or around your subject will likely produce far more interesting and compelling compositions than would likely be the case simply by zooming in.

Please remember that photography is a physical endeavor and your best photographs will often be those that were made by changing your camera's relationship to the subject. And the best way to explore this concept is through moving around, closer to or further away from your subject.

The focal length of your lens will also make a difference. But don't forget to move. It costs nothing and can produce very creative results.

Glenn Guy, Travel Photography Guru