The F4 compromise

In the land of zooms, between the cheap entry-level kit lenses and the expensive professional F2.8 options lies the F4 compromise. This ‘sweet spot’ promises to deliver the professional feel, features and image quality of an F2.8 at a reduced weight, size and price thanks to its one-stop-slower maximum aperture. Is this a smart compromise or a middle ground that makes no sense?

Compared to the kit lens

Camera kits (body and lens packages) are often assembled with the lowest-end zoom lens available from the manufacturer. The kit lens is a way of providing a complete camera for those at the start of their photographic journey: it’s the least expensive way to get started. Fujifilm’s 18-55mm F2.8-4 lens stands as a notable exception to this rule, so let’s just set that one aside at this point.

The Canon RF 24-105 F4 sits in the middle between the pro ready Canon RF 24-70mm F2.8 and the consumer friendly RF 24-105 F4-7.1.

For new photographers overwhelmed with all the lens options out there, the compact size, light weight and affordability of basic lenses are all very attractive qualities. Many of us (myself included) started with the kit zoom. Good images are possible using these slow, variable-aperture lenses, but in time it’s only natural to desire the quality and features of higher-end glass as you hone your skills.

The pro-oriented Nikon Z 24-70mm F2.8 S and the more consumer-friendly Nikon Z 24-70mm F4 S.

The desire to improve on a basic lens can be for many reasons: sharpness, light gathering, weathersealing or other benefits. While those with the resources can jump directly to their brand’s premium (and pricey) F2.8 zooms, there’s a middle ground. A step up from the standard kit lens is a collection of zoom lenses often featuring a maximum (and constant) aperture of F4. These lenses offer more professional construction, generally sharper glass and a maximum aperture that doesn’t change when you zoom.

There have been a good number of F4 zooms in the past, but I’m going to call out Canon’s EF 70-200mm F4 L USM, introduced in 1999, as the first of the modern generation to popularize the F4 trend. This was possibly the first F4 lens that offered virtually everything the more expensive F2.8 version did – with the sole exception of the F2.8 aperture. This lens even looked like a miniature version of the popular F2.8 version, including the distinctive white paint and red stripe. Selling for about half the price and weighing half as much it became a popular lens in the new era of digital photography where higher ISOs could make up for the one-stop-slower aperture.

One of the most attractive qualities of this 70-200mm F4 lens was the fixed maximum aperture. When exposure settings are dialed in, it’s common to zoom back and forth a bit to capture a variety of compositions. Those with variable-aperture lenses are familiar with the scene darkening or brightening as you do this, requiring you to adjust shutter speed or ISO at the same time. A fixed maximum aperture means that you can maintain your settings when you adjust the focal length of your lens.

Canon’s current 70-200mm options: (left) the RF 70-200mm F2.8 L IS USM and (right) the RF 70-200mm F4 L IS USM.

The second major lens to prove the concept was the hugely popular Canon EF 24-105mm F4L introduced in 2005. Often sold as a premium kit lens, it proved to be very popular as a lighter and lower-cost option to the 24-70mm F2.8.

In short the F4 options provided a professional tool that was just a bit smaller, lighter and less costly. It was a good idea that spread quickly.

Compared to pro F2.8 lenses

Measured with Canon and Sony mirrorless options, F4 zoom lenses are on average 57% lighter, 25% shorter and 44% less money than the comparable F2.8 lens.

A multiple exposure image to show the size difference between the Canon RF 24-70mm F2.8 and the Canon RF 24-105mm F4.

Every camera system must offer a collection of professional zooms with a maximum aperture of F2.8 to be taken seriously. The classic holy trinity of F2.8 zooms has historically been a 16-35mm, a 24-70mm and a 70-200mm. A variety of other focal lengths have also been offered at F2.8, from the wide (14-24mm and 17-28mm) to the long (70-180mm).

Options within the Sony brand for full-frame are the FE 24-70mm F2.8 GM II and the Vario-Tessar T* FE 24-70mm F4 ZA OSS.

The fast F2.8 aperture of these zooms makes them ideal for shooting a wide variety of subjects in less than perfect lighting. They are particularly good when photographing moving people, as the relatively fast aperture allows for a faster shutter speed to avoid subject blur. The F2.8 aperture is also useful for creating a shallow depth of field. While not offering the extreme background blur of an 85mm F1.2 or 135mm F1.8, the F2.8 setting will suffice to isolate a subject in most situations.

The problem with the F2.8 zoom is that it’s more than some people need or can afford. That’s where the F4 zooms come in, promising similar features and quality in a smaller, lighter and above all more affordable package. For many, getting a sharp, perhaps weathersealed lens at about 50% of the price is an attractive option.

Comparisons between F4 and F2.8 options almost always result in a modest win for the faster lens. Whether you look at image quality, flare, construction, weathersealing, buttons and switches, focus speed or some other aspect, the differences will usually be better for the F2.8 lens – but only slightly.

The biggest difference is that one-stop aperture difference and all that comes or goes with it. Let’s look into that.

Low light

When working in low light conditions every extra stop can have a big impact. Using a lens with a maximum aperture of F4 rather than F2.8 means either using a slower shutter speed or a higher ISO. While it’s always better to have an F2.8 option in the field, there are a number of techniques you can use to make up for it depending on the situation.

The use of a slower shutter speed can negatively impact your image in one of two ways – camera movement or subject movement. It’s possible that adjustments to your shooting style or approach could make shooting at a slower shutter speed acceptable.

ISO 160 | 1/125 sec | F4 | Canon EF 70-200mm F4 L IS USM | 160mm Photo credit: John Greengo

If you are hand-holding you could instead use a tripod, monopod or other device to provide a more stable platform for your camera. Many cameras also offer IBIS (In-body image stabilization) or lens stabilization. The best systems claim up to 8 stops of stabilization, which, if accurate, means being able to shoot with a 50mm lens at a shutter speed of 4 seconds. My personal tests of such systems have found the manufacturers to be a bit optimistic in their claims, but still with very impressive results. With a quality IBIS system it’s possible that using a shutter speed one stop slower will have no impact on your final image – at least in terms of controlling camera shake.

For the challenge of moving subjects there are options besides a faster aperture for solving the problem. You could shoot at a different time of day, in better light; you could bring your own lights; or you could just shoot when your subject isn’t moving as quickly. True, these solutions will only work in some situations; in others the only realistic option will be to bump the ISO up one stop to accommodate for a faster shutter speed.

The impact on your image of shooting at a stop higher ISO may be significant or negligible depending on the ISO value in question, what camera you have and how your image will be viewed in its final form. Cameras lose image quality when given less light, and as you provide less and less light, the greater the impact from each one-stop reduction. Moving from ISO 400 exposure to ISO 800’s exposure will be very hard to perceive in most cases. Moving from ISO 6400 exposure to 12800’s may be a dealbreaker or may not, depending on the camera, the scene and how the photo will be used.

Depth of field

The other advantage of a one-stop-faster lens is its offering shallower depth of field. An aperture of F2.8 is a great tool when trying to separate a subject from the background, for example in portrait photography. While prime lenses, and a few super-fast zooms (eg Canon RF 28-70mm F2, Sigma 24-35mm F2) will offer an even wider aperture, F2.8 is usually good enough for most professional portrait situations. Yes, of course the beautiful bokeh of an 85mm F1.2 is something to behold, but it isn’t necessary to become a professional portrait photographer.

If three options wasn’t enough Canon offers a fourth “normal” zoom option with an F2 aperture. Left to right: Canon RF 28-70mm F2 L USM, Canon RF 24-70mm F2.8 L IS USM, Canon 24-105mm F4 L IS USM, Canon RF 24-105mm F4-7.1

When working with an F4 lens for portraits, backgrounds will not have as much blur as those shot with an F2.8 lens. So who will notice this? Anyone, when they’re viewing a side-by-side test. It’s a relatively easy comparison when viewed together. Viewed on its own, however, it’s very difficult. Only the most skilled and experienced photographer could determine an F4 vs F2.8 aperture setting without seeing a side-by-side comparison. Ask a non-photographer about the image quality or bokeh difference between an F2.8 and F4 shot and you’re likely to get a shrug and an “I guess so.”

70mm | F2.8	70mm | F4	105mm | F4
Canon RF 24-105mm F4 L IS USM | ISO 100 Can you make up for the depth of field difference by zooming in to 105mm and moving back? The longer focal length technically yields a shallower depth of field, but combined with the increased distance, changing from 70 to 105mm has a minimal impact on the blur of the background.

There is no getting around the fact that the F2.8 lens will always have that extra stop of separation. However, with knowledge some of those differences can be minimized. For a portrait you could move a bit closer to your subject and frame them a bit tighter for a resulting shallower depth of field. Alternatively you could arrange your subject further from the background, which would result in a background that’s a bit more out of focus.

Of course you can also use these techniques with an F2.8 lens for even shallower depth of field, so we’re right back to where we started. The question is how much blur do you need. I believe that if you are photographing for personal enjoyment the F4 lens will do the job well enough on full frame, at least. However, if you or other judges are going to be comparing your images to those of other photographers, you can bet that much of the ‘competition’ will be using F2.8 or faster glass.

ISO 800 | 1/125 sec | F4 | Canon EF 70-200mm F4 L IS USM | 165mm Photo credit: John Greengo

One point is worth mentioning for those that don’t know: it doesn’t matter if you have an F2.8 or F4 lens when you’re not shooting wide open. If you find yourself shooting at F8 or F11 frequently, that F2.8 aperture lens isn’t doing anything for you, at least when it comes to depth-of-field or shutter speed.

While not exactly the same focal length, all three of these Sony lenses offer different takes on the normal-range zoom. Left to right: E 16-55mm F2.8 G, Vario-Tessar T* E 16-70mm F4 ZA OSS, and the E PZ 16-50mm F3.5-5.6

What about on crop sensor cameras?

The relationship between F2.8 and F4 lenses described above applies mostly to full-frame cameras. For smaller-sensor systems the differences still apply, but the size and price differences are likely to be less significant, and you’ll get less control over depth-of-field.

In the Micro Four Thirds world the difference between F2.8 and F4 lenses is smaller, at least when it comes to a normal zoom range. Left to right: Olympus M. Zuiko Digital ED 12-40mm F2.8 PRO and Olympus M. Zuiko Digital ED 12-45mm F4 PRO

The smaller sensor generally results in smaller lenses, and it makes an F2.8 aperture a bit more affordable and lighter than the full-frame equivalent. One could view the option of getting an F2.8 lens over an F4 as a way of making up some of the sensor size difference.

What to buy

The best lens for you depends on your subject, the available light and your end use. Perhaps most important will be your personal standards for what is ‘good enough.’

For the working professional the F2.8 is that extra edge that is often necessary to keep up with the Joneses. If you’re competing with other photographers for gigs, jobs and clients it would be wise to assume that much of your competition will be working with the ‘best’ gear available. When I took a job where I knew I would be photographing people in a variety of low light situations and I needed to come back with usable professional photos I went with an F2.8 lens without a second thought.

Yet for my personal photography, where I have a much more forgiving standard, I love an F4 zoom lens. I’ve owned a bunch of them and have loved using every one. Yes, from time to time I wished for the faster aperture, but I made do. I don’t recall any shots that I missed because of it, though realistically there were probably a few. I know how to work around challenging situations and know that 99.99% of the people viewing my images will have no idea that I’m using an F4 lens. (Now that I’ve written an article about it, that may change.)

For those who are willing to compromise just a bit, or want more portable and affordable gear, F4 zooms are a perfect fit.

On the other hand even in everyday use I noticed and have very much enjoyed the step up from entry-level lenses in quality and ergonomics, as well as the constant maximum aperture. In that sense I found F4 zooms to be like miniature versions of the F2.8 options.

ISO 400 | 1/80 sec | F4 | Canon EF 70-200mm F4 L IS USM | 70mm F4 lenses make ideal travel gear as they allow for professional quality images in a compact and lightweight package. Photo credit: John Greengo

I think the F4 zoom is the perfect lens for the photographer who wants a sweet spot of quality, size and price. You’d probably be surprised at what you can get away with shooting an F4 lens, given modern cameras’ technology (ISO and IBIS). For professionals where having the best piece of gear outweighs the cost or size consideration, F2.8 will be the standard. But for those who are willing to compromise just a bit, or want more portable and affordable gear, F4 zooms are a perfect fit.

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John Greengo specializes in photographic education through online training, books and international photo tours. His photographic teachings have been viewed by millions around the globe.

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