Choosing between the Canon 70-200 2.8 or 4.0?
By Dwight Arthur, 2011/01/28
Q: How much better is a Canon 70-200 F:2.8 lens than a Canon 70-200 F:4.0? It's only one stop faster and it's way more money! Will I see a difference?
A: A good question with no simple answer! While the following response is about two specific lenses, many of the important principles discussed are equally valid for comparing telephoto zoom lens choices for other brands.
First of all, there are a lot of Canon 70-200 lenses, including two current Canon 70-200 F:4 lenses: one with and one without image stabilization. Let's start by stating that I would definitely spring for the extra cost of IS, as there are many situations in which it is sure to give you sharper results. I will never again purchase a long lens without IS technology--it's just too valuable. There are also two 70-200 f:2.8 IS lenses currenty available: the old one, which has a great reputation, and the new MkII: with improved IS, slightly better auto-focus and even better optical performance (according to the talk on the web--I've never compared them directly myself). Assuming that you are talking about the 4.0 IS and the latest 2.8 IS, then here's my thoughts:
First off, both of these lenses, by general consensus and my own observations are outstanding performers in pretty much every respect. They are both wonderfully sharp, with great auto-focus, and low flare. While the 2.8 'bench tests' somewhat better in every respect, on any real-world practical level, in the hands of a typical user, it's questionable how often these differences of pure optical performance would be significant. They're both great lenses that will run circles around pretty much any other alternatives for a Canon camera. Sure the 4.0 is not quite the performer the 2.8 is, but I wouldn't hesitate to use the 4.0 lens on assignment, wondering if my client would question the results based soley on optical quality specs!
That being said, there are some differences of a more practical vein that you do need to consider when choosing between these lenses. Choosing a lens should never be soley about pure optical performance!
"Choosing a lens should never be soley about pure optical performance!...I've had female students regret the purchase of the huge 2.8 lens just because of shooter fatigue on long assignments."
Weight: the f:4 lens is a LOT lighter (about 1/2 the weight) and that is sometimes a big advantage when travelling on foot for any distance or even when having to hold the camera up at your eye for extended periods of time. I've had female students regret the purchase of the huge 2.8 lens just because of shooter fatigue on long assignments. Bigger in itself is never better unless you carry your lenses around just to impress the other photographers!
Lens speed: If you are using either of these lenses at apertures of f:8 or smaller you are not likely to see any obvious difference that can be solely attributed to optical performance, no matter how close you look. However, when using larger apertures you likely will see some differences—maybe not profound but probably enough to matter. When shooting at f:5.6 the 2.8 lens will be sharper than the f:4, especially in the corners, and show less vignetting as well, simply because you are stopping it down 2 stops from wide open. I've never seen a lens that doesn't improve at two stops down compared to one stop down (as the f:4 lens would be in this instance). Same thing applies to shooting at f:4. At this aperture the f:4 lens is shooting wide open and the 2.8 is one stop down so it's going to perform better. Taking it even further, to 2.8, well you can only do that with the 2.8 lens so its clear who's the winner there! From this you might conclude that if your are not planning on shooting at the larger apertures, sticking to f:8.0 or smaller, there is no advantage to the bigger, heavier, costlier 2.8 lens. Think again. This is hardly the end of the discussion. There is still further added value in the faster lens!
"There's no advantage to a lens with great optical quality if it is often not properly focusing!"
Focusing: It is no small thing that the 2.8 lens produces a noticably brighter image and renders shallower depth-of-field in the viewfinder, both of which make it noticably easier to focus-- automatically or manually, especially in low light. There's no advantage to a lens with great optical quality if it is often not properly focusing! This is, in my opinion, reason enough to opt for the faster lens.
"Image stabilization is NOT a direct-equivalent solution for low-light work to using a larger aperture."
Also, while It is true that the f:4 lens, with its wonderful new-and-improved IS technology, is going to filter camera-shake blur very effectively when shooting in low light even with slow shutter speeds, you can't say that this eliminates the need for the faster lens. Image stabilization is NOT a direct-equivalent solution for low-light work to using a larger aperture. IS does nothing to prevent subject motion blur, only camera motion, so if the low light work you are doing involves moving subjects then the faster 2.8 lens is still an advantage. By using an aperture of 2.8 instead of 4.0 you can use twice as fast a shutter speed, resulting in half the subject-motion blur. This can be mission critical in some situations. One strong caution on this point though: at 200mm the lens will be producing extremely shallow depth-of-field so what you have gained in sharpness by using a faster shutter speed may be lost in focus blur due to shallow DOF in some circumstances. Also, if your focusing is not spot-on you might not be happy with results either, due to the same issue of extremely shallow DOF that 2.8 generates.
Now maybe you are thinking, "Yeah, but since my camera is so outstanding at high ISO settings, I can just turn up the ISO to get the fast shutter speed I need to stop motion blur." While this is indeed a valid solution, it will still lessen image quality somewhat through increased noise and diminished shadow detail, so the result is not equivalent to using the faster lens at a lower ISO to arrive at an acceptable shutter speed.
"If you have not yet explored using large apertures to achieve shallow depth-of-field you really are missing out on something beautiful!"
A final, extremely significant point that puts the 2.8 lens out front for some photographers is the following: large aperture settings are a huge asset in creative control of image appearance, even if you don't need the extra light-gathering power due to ample light or your camera's great high-ISO performance. If you have not yet explored using large apertures to achieve shallow depth-of-field you really are missing out on something beautiful! There's no more effective way to emphasize your subject than by making it the only sharply rendered object in the frame. A clearly depicted subject with none of the context fighting for attention is a powerful statement that a lot of photographers under-utilize. The 70-200 2.8 is one of my favourite lenses, along with the amazing but cheap 50mm 1.8, for achieving this effect!
Bottom line is that I'd love to own a 70-200 f:4 just for hiking and other times when weight strain is an issue, but I had to go with the 2.8 for its ability to create the look that I love, plus it's extended capacity for low-light action photography. Too bad money doesn't grow on trees...then I'd own both!