The Mirrorless Lens Conundrum

My 24-70mm f/2.8 S-line lens for the Nikon Z cameras showed up recently, as did everyone else's. Nikon's shipments immediately started triggering the "should I get the f/2.8 or the f/4 lens" type of questions in my In Box. 

bythom nikkor 24-70mm

This type of question isn't new. In the DSLR full frame world, we've long had the primary zoom lens trio—wide angle zoom, mid-range zoom, telephoto zoom—available in f/2.8 and f/4 variants. (In the crop sensor world, we tend to get only one higher end choice from the DSLR makers, with everything else being variable aperture kit lenses.)

In that full frame DSLR world, the differential between the two aperture choices tends to be relatively modest and repeatable. In both the Canon and Nikon zoom sets, the f/2.8 lenses perform better optically than the f/4 lenses at f/4, they can gather another stop of light (obviously), but they're heavier and more expensive. In almost every case, the tradeoff most people get down to is that stop of light for increased size and price, though. 

For example: in the Canon DSLR world the 70-200mm f/2.8 is US$2100 and the f/4 is US$1300. For Nikon, the 70-200mm f/2.8 is US$2800, the f/4 is US$1400, or half the price (you don't get the optional tripod foot, though). Because of those pricings, the Nikon DSLR user is much more tempted by the f/4 lens than the Canon DSLR user. At least they were until the f/2.8E came out and just blew the socks off optical expectations for a telephoto zoom.

In the mirrorless full frame world, things have been a little different. The Sony 24-70mm f/4 (US$900) is not a particularly good lens as it smears badly already by the APS-C frame line, while the Sony 24-70mm f/2.8 (US$2200) is an excellent lens. Meanwhile the Sony 12-24mm f/4 and 16-35mm f/2.8 don't match up in focal length (both are excellent, though the 16-35mm is better at the equivalent focal lengths and apertures). Finally, the 70-200mm f/2.8 and f/4 in the Sony lineup basically mimic what you find in the DSLR world: substantive price differential, reasonable size/weight differential, modest optical differential.

Canon and Panasonic don't yet really have any "pairs" for the basic three zooms in their mirrorless systems yet, but Nikon is now delivering two 24-70mm lenses. So the question has started to come up: which one? (Note: I've reviewed the f/4 version very favorably, and I'm just starting my review process on the f/2.8 version, so what I say here is very preliminary.)

Nikon didn't make this easy. The 24-70mm f/4 is one of the best "kit" lenses you'll find. At the kit bundle implied price of US$600, it very well may be the best mid-range zoom by a large margin at that price point. Even at the retail price of US$1000, you just don't find many zoom lenses that good at that price point. I'd say that you're being somewhat foolish if you buy a body only in the Nikon lineup instead of the body+24-70mm kit. Moreover, in terms of size and weight, the f/4 version keeps the basic body+lens combination substantively smaller and lighter than you're used to with full frame DSLRs.

But...

The 24-70mm f/2.8 is a better lens, even just based upon some early initial shooting. As much as I like the f/4 zoom, the f/2.8 is so far looking optically better at the same focal length and aperture combos with very few exceptions. (The f/2.8 seems to have a small bit of waviness to its sharpness at a few apertures and focus distances, though, where the f/4 doesn't; so there are points on the frame at a couple of focal lengths where the f/4 can top the f/2.8. That said, the vast majority of the frame on the f/2.8 is going to produce better results than the f/4 at the same focus distance, aperture, and focal length. Why the waviness in the f/2.8 acuity? Probably due to the aspherical elements and how they interact with the optical path as they move.)

Which brings us to: why do you want f/2.8? Two things: (1) a stop more light capability; and (2) a stop more DOF isolation ability. You really have to figure out how much those two things are worth to you (in any brand zoom pair, but particularly in the Nikon 24-70mm duo, as the price difference can be as much as US$1700). Moreover, the f/2.8 version is substantively heavier than the f/4 version, though it's still smaller than you may be used to with DSLR 24-70mm f/2.8 lenses.

There's no question in my mind at the moment that the perfect travel combo for the Z's right now is: 

  • 14-30mm f/4
  • 24-70mm f/4
  • 70-300mm f/4.5-5.6 AF-P on FTZ

(For you Sony users:

  • 12-24mm f/4
  • 24-105mm f/4
  • 70-200mm f/4)

That's a highly competent and reasonably small kit that covers an incredibly wide focal range.

The conundrum is this: what if you do sometimes (or often) value that extra stop of light and DOF isolation (plus a bit more optical quality)? By this time next year, we'll have 14-24mm, 24-70mm, and 70-200mm f/2.8 lenses in the Nikon line, and we already have 16-35mm, 24-70mm, and 70-200mm f/2.8 lenses in the Sony lineup. Thus, you should be thinking about this now, not later.

I can't really answer the question for you, as there are clear tradeoffs you have to come to conclusions about. I can only make sure that you ponder your circumstances carefully and provide as much information as I can to help you make your decisions. 

In both the Nikon and Sony travel kits I mention above, we've never had it so good with full frame. That's six lenses that produce really strong results; better than the kit-lens results we got in DSLRs through those same focal ranges, IMHO. But it's also starting to turn out that the f/2.8 zooms are pushing beyond what we got with the DSLRs, too. 

Thus, the conundrum is multiple. There's the usual f/2.8 versus f/4 decision, but we're also starting to see a differential between DSLR and mirrorless in these lenses, too. The future is so f/2.8 bright, I gotta wear shades (yes, a Timbuk3 reference).

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