Shopping for a new lens: Lens Aperture

Hey guys. Welcome back to our second post in Shopping for a new lens article series. Last time we talked about Image Quality, which you can check out right here if you haven’t already done so. Today we will be talking about Lens Aperture, which is among the most important things you might wanna look for when adding a new lens to your collection.

What is aperture?

Most simply put, aperture is a hole or an opening in the lens controlling how much light travels through hitting the film or digital sensor and recording an exposure.

What you also need to keep in mind when shopping for a new lens is that the wider the maximum aperture opening of the lens is (the lower the f-stop number is), the shallower a depth of field you’ll be able to achieve, and the more light you’ll be able to capture in poor lighting situations.

A good lens is one with wider maximum aperture, and an ample range of lens openings to allow for many varying picture-taking situations, allowing you to take photos in low to high lighting conditions.

In general, a lens with a maximum aperture opening of f1.4 to f2.8 or wider is considered fast (which means it allows for shooting in low light with faster shutter speeds or slower ISO settings), where as a lens with a maximum aperture of f8 is considered slow. A lens with a maximum aperture opening of f3.5 to f5.6 is ok for general lighting situations. So you would always want to shoot for wider maximum aperture lenses (for as much as you can afford or are willing to pay).

Some exceptional lenses can have f-numbers below f1.0. For example, both the current Leica Noctilux-M 50mm ASPH and a 1960′s-era Canon 50mm rangefinder lens have a maximum aperture of f0.95. Such lenses tend to be optically exotic and very expensive. For instance, when the Leica Noctilux first came out, it was priced at a stunning $11,000.

Zoom lenses tend to be slower than their prime lens counterparts at a given focal length. That is due to more optical components involved in a zoom lens built.

Furthermore, typical affordable zoom lenses will have a varying maximum aperture opening throughout the zoom range. This means that a standard 1:3.5-5.6 18-55mm zoom lens would have a maximum lens opening of 3.5 at 18mm stepping down to a maximum opening of 5.6 when zoomed all the way in at 55mm. while high-end zoom lenses would have a constant (non-changing) maximum aperture opening throughout the zoom range. That is because it is generally harder and more expensive to keep the effective aperture proportional to focal length at long focal lengths.

As for the minimum lens opening, the narrower aperture opening your lens can provide you with, the more it will be useful for you to shoot in extremely bright light conditions, or to shoot with slower shutter speeds to create creative blurring and other effects. Of course you can always use neutral density filters (ND filters) to cut back the amount of light traveling through your lens hitting your film or digital sensor if you wanna expose at slower shutter speeds without causing overexposure.

How do I spot the maximum aperture opening of my lens?

To be able to tell the maximum aperture opening for a specific lens, you could either review the lens’ specifications on the web, or you could alternatively simply look at the front of the lens. There will be a code next to the lens’ focal length specification that will say something like 1:1.4, or 1:4.5, or 1:3.5-5.6, or something like that.

The numbers after the "1:" are what you need to pay attention to. For a prime lens that says 1:1.4 at the front means that that lens’ maximum aperture opening is f1.4. For a zoom lens that says 1:3.5-5.6 at the front means that the lens’ maximum opening at the shortest focal lens (widest angle of view) is f3.5, and at the longest focal length (the narrowest angle of view) is f5.6. So there you go, it’s as simple as that =)

This concludes our post talking about lens aperture, which I consider along with million other photographers I’m sure, as one of THE most important factors you’ll need to look at when shopping for your next lens.

I hope you found the info here helpful in bringing you more into light, and eliminating yet another confusing decision you’ll have to make when replacing your lens. Next time I’m gonna be talking about Lens Minimum Focusing Distance, which is yet another very important specification to look for in your next lens. Be well, and stay tuned…