Is an f2.8 lens better than f4?

I like to keep up with the goings on in photography by listening to podcasts. A particularly opinionated broadcaster is Jared Polin. A few weeks ago, he had an amusing rant that f2.8 lenses are always better than f4 equivalents. There is a massive difference in price between the two versions. For example, a Canon RF 24-70 f2.8 retails at £2389.99 compared to the Canon RF 24-105 f4, which you can buy for £1439.99. During Polin’s diatribe, he stated that you could clearly see the difference between an f2.8 lens and an f4 one. This week, I carried out a semi-scientific experiment to establish if the extra £900 is warranted in buying the faster lens.

F2.8, F4 – you’re confusing me…

If you are relatively inexperienced in photography, you’ll probably ask what I mean when discussing f2.8 or f4 lenses. Camera manufacturers always refer to the biggest aperture possible on the lens. The 24-70 f2.8 has an aperture range available from f2.8 to f22. The 24-105 f4 has an available range from f4 to f22. In practice, this means that when shooting at the widest aperture in both lenses, there is twice the amount of light that can be captured on the more expensive lens than the cheaper one.

There are some good uses for this extra light. If you are a wedding photographer, an extra stop of light inside the church will reduce the amount of ISO needed by half. This means that in low light, there will be less noise in your photos. Similarly, someone taking astrophotography pictures will see a reduction in the noise levels with the addition of an extra stop of light.

So, the f2.8 is better?

Before we compare photographs from each lens to look at quality, it’s worth looking at some physical differences.

The extra stop of light in the f2.8 lens needs three more elements (or pieces of glass) between the front part of the lens and the back. The extra three bits of glass add 200g to the f2.8 lens, making it weigh in at 900g. The f4 lens, by comparison, weighs just 700g. If you’re walking up a mountain and shooting at f11, then the 200g reduction of weight might be very welcome if the quality is the same.

Another difference between the lenses is how close you can focus. The f4 lens has a shortest focusing distance of 45cm. In contrast, the f2.8 version can focus at 21cm at the 24 end of the zoom, increasing to 38cm at the widest angle.

The final difference is obviously the distance that you can zoom. While both lenses have the widest end of the zoom at the same angle, the f4 lens can zoom in further. If you don’t need the widest aperture, you have more flexibility with the cheaper lens. That’s why the f4 lens can often make a better ‘walk-around’ lens, say, for travel photography.

What about quality?

At the end of the day, how good your photos look is usually the defining characteristic that should determine a purchase. (As long as you have a limitless budget!). To decide if there was a difference, I took both lenses out and took the same scene, using the same settings in settled weather conditions. The methodology I used was to shoot both lenses at f11 at the 24mm and 70mm ends of the lenses. I repeated the exercise, shooting at f4. Let’s look at the differences.

F11 at 24mm

The first noticeable difference between the two lenses is that the f2.8 lens appears to have a wider angle at 24mm than the f4 version. I only have one of each lens to carry out the test, so I can’t say if the difference is due to the models I have. I would like to hope that Canon’s manufacturing process is pretty accurate and the difference is quite significant.

Zoomed in at 300% in Lightroom, we can start to pixel peek. It’s hard to see much difference between the detail captured in the two lenses. If anything, the most significant change is in brightness. The f4 version on the left is marginally brighter than its f2.8 bigger brother.

F11 at 70mm

Again, we can see a difference between the amount of the image we see on the 24-105 lens. The f2.8 version gives us a slightly wider view again. The difference in brightness is even more apparent when we go to the far end of the zoom. The f2.8 lens is definitely much darker than the f4 lens (seen on the left). Because of the difference in brightness, it is hard to determine whether we see more detail in the f2.8 lens. It could be the case, but the difference really is minimal.

F4 at 24mm

The issues of brightness and zoom remain consistent as we open up the aperture. This time, however, zooming in at 300%, the f2.8 (on the right) is definitely sharper. The tree in the top right corner is the easiest place to see this. There is an improvement in quality using the more expensive lens.

F4 at 70mm

In the final view, we’ve kept the aperture at f4 on both lenses and moved the zoom to 70mm.
With these settings, the sharpness of the f2.8(on the right) is undoubtedly better.

OK, so the f2.8 lens is better

It’s pretty easy to look at the sets of photos above and conclude that the f2.8 version of the lens is better. For an extra £900, I hope that would be the case. The more important question is if the extra stop of light at the widest aperture is worth those extra bank notes. To answer that question, you must be honest about how you will use the lenses.

If you look at the images with sliders, it’s really hard to see any difference in quality between the images taken on each lens. It’s only noticeable when we zoom in to 300%. In reality, most people won’t look so closely at images to see this difference. If you are shooting Commercial photography, that will be increased to billboard size – maybe it will be seen. If you are posting to Instagram, then your viewers will see no difference.

Similarly, if you are a photographer working in lower light conditions, the extra stop will allow you to shoot with half the ISO or twice the shutter speed. If those things are important to your work, then £900 will be a good price to pay. If you’re shooting in good light during the day, you’ll probably be okay with the cheaper f4 lens.

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About the author

As well as running Edinburgh Photography Workshop, Rich Dyson is a professional photographer. His photographs are regularly used in newspapers such as The Times, Guardian and Daily Telegraph. He also had two solo exhibitions and was featured in a members-sponsored exhibition in the Scottish Parliament. You can see and buy his photography at richdysonphotography.com.