One swallow does not a summer make said Aristotle, suggesting the dangers of looking for trends based on single examples. Even with this in mind, I'm pleased to see two manufacturers introduce 70-200mm equivalent zooms for APS-C cameras at this year's Photokina. First Fujifilm introduced its XF 50-140mm F2.8 R LM OIS WR, and then Samsung followed suit with its 50-150mm F2.8 S. This can only be a good thing, since I'd argue they make more sense for many photographers than actual 70-200mm lenses do on APS-C. Let me explain why:

Easy as APS-C

APS-C has been the de facto standard format for almost a decade while full frame was almost unattainable for most photographers. With the exception of a handful of professional grade (and professionally priced) models, the vast majority of DSLR users have been shooting the smaller format. Only now is its primacy being challenged, and even that's only true at the top-end of the market. And yet it's interesting to note that most manufacturers (including third-party lens makers), have concentrated on continuing to make 70-200mm lenses, rather than lenses offers the equivalent range on APS-C.

Mirrorless makers don't have the benefit or baggage of pre-existing lens lineups. And I think it's great that they're creating lenses that take advantage of the APS-C format, rather than hobbling it by building lenses intended for a totally different format. Like any format, APS-C offers a particular size/image quality balance, so it surely makes sense to seize as much of that size benefit as possible and use lenses designed with this in mind.

Isn't more zoom better?

A 50-150mm won't give the same reach as a 70-200mm lens would on APS-C, but it will give essentially the same range that those older designs offered for film-era photographers.

There's a school of thought that says that, if you're going to buy a telephoto lens, then you probably want as much reach as possible. And there's certainly a logic to that: telephotos are probably the class of lens that best continues to serve its intended function when mounted on a smaller sensor size. However, while you can argue that a 105-300mm equivalent F2.8 is better than a 70-200mm equivalent, by dint of offering more reach, there's also a counter-argument to be made.

Size and weight

Two of the great advantages of 70-200mm equivalents are that they can be smaller and lighter than actual 70-200s. What you lose in reach is made up for in terms of portability. Fujifilm and Samsung aren't the first companies to offer 70-200mm equivalent lenses (Pentax and Tokina both introduced 50-135mm F2.8 zooms in 2007, while Sigma has produced two distinct models over the years), but I think they're right to do so.

Not only are 50-150mm lenses easier to carry around, they can also be small and light enough that you can more readily swing your camera around when shooting portraits. As an example, the original Sigma 50-150mm was around two-thirds the length and around half the weight of the company's current 70-200mm F2.8 (though it should be noted that smaller lens was not stabilized).

  Fujifilm 50-140 F2.8 Samsung 50-150 F2.8 Nikon 70-200
F2.8 VR II
Canon 70-200
F2.8 L IS II
Sigma 70-200
F2.8
Dimensions (mm) 83 x 176 81 x 154 87 x 206 89 x 199 86 x 198
Weight 995g 915g 1540g 1490g 1430g

The Fujifilm and Samsung lenses are both a bit heavier than the Sigma, Pentax or Tokina, thanks to a combination of the pushes for premium optical performance and build, along with the inclusion of image stabilization (which seems very impressive in the case of the Fujifilm). For example, the Fujifilm consists of a whopping 23 elements in 16 groups - far beyond the 18 element / 14 group designs of the older lenses. However, they're still considerably lighter than the current generation of 70-200s.

One of the things I really enjoy about 50-150mm lenses is that they're easier to wield than 70-200s tend to be.

I owned a 70-200mm lens for several years and rarely used it, because I couldn't face carrying it around.

However, a 50-150mm (in this case the first-generation, 770g unstabilized Sigma) was light enough that I had it with me and was able to quickly grab a shot when I bumped into the then National Circuit Race and World Track Team Pursuit champion.

Cutting costs

The other advantage of 50-150mm lenses is that they can be less expensive than 70-200s. The latest, pro-grade 70-200mm F2.8s from Canon and Nikon will set you back $2300 and $2400, respectively, whereas both Fujifilm and Samsung are looking for $1600 for their lenses. Both lenses are image stabilized and, based on our experiences with pre-production models seem to focus very rapidly. The complexity of the designs suggests both brands are taking images quality seriously (though, of course, we'll need to spend time shooting with them to know for sure).

  Fujifilm 50-140 F2.8 Samsung 50-150 F2.8 OIS Nikon 70-200
F2.8 VR II
Canon 70-200
F2.8 L IS II
Sigma 70-200
F2.8 OS
Elements/
groups
23 / 16 20 / 13 21 / 16 23 / 19 22 / 17
MSRP (US) $1599 $1599 $2399 $2299 $1399

But what about the f/4s?

If the size, weight and price of a 70-200mm equivalent seems appealing, then wouldn't Fujifilm and Samsung be better-off making 70-200mm F4 lenses like those that Canon, Nikon and Sony offer? 

I'd argue no. While they are similarly sized, sometimes lighter and usually a little cheaper than the Fujifilm and Samsung, they're also less bright. Personally I think the extra low-light capability and control over depth-of-field that the 50-150mm F2.8s offer is probably more valuable than the extra reach and slight cost saving of using a 70-200mm F4 on APS-C.

  Fujifilm 50-140 F2.8 Samsung 50-150 F2.8 Nikon 70-200
F4 VR
Canon 70-200
F4 IS
Elements/
groups
23 / 16 20 / 13 20 / 14 20 / 15
Dimensions (mm) 83 x 176 81 x 154 78 x 179 76 x 172
Weight 995g 915g 850g 760g
MSRP (US) $1599 $1599 $1399 $1299

If you've already got a full frame camera, then a 70-200mm F4 offers a very similar set of capabilities to a 50-150mm F2.8 on APS-C (same zoom range, similar light capture and depth-of-field). But any cost benefit of buying a 70-200mm F4 rather than an equivalent zoom is lost if you have to buy a full frame camera to gain access to that capability.

And what of Micro Four Thirds?

The new lens I'm not mentioning here is the Olympus 40-150mm F2.8 Pro. This is because, although in one respect it's a very similar lens to the other ones I'm discussing, its effect on a Micro Four Thirds body is very different (an 80-300mm equivalent zoom is a rather different thing)

The more natural comparison is Panasonic's 35-100mm F2.8. Like the Fujifilm and Samsung, it's able to be small and light because it's used on a smaller format. I think it makes just as much sense as the Fujifilm and Samsung. Its depth-of-field and light capture costs (it's most directly comparable to a Full Frame 70-200mm F5.6) are pretty much proportionate to just how light and small it's able to be. But at a mere 360g and 99mm long, it's a very usable lens indeed.

Making sense with mirrorless

The increasing ambitions of mirrorless cameras are clearly what's driving the latest announcements. Both Fujifilm's X-T1 and Samsung's NX1 aim to offer effective continuous autofocus in smaller-than-DSLR packages. These 70-200mm equivalent lenses fit well with that 'more portable' ethos, while still incorporating image stabilization, environmental sealing and all the other features you might expect from a high-end telezoom.

I always enjoyed shooting with the original Sigma 50-150mm F2.8 and always looked forward to getting to shoot with the 50-135mm F2.8 when I reviewed a Pentax DSLR, but they didn't ever sell terribly well. The arrival of increasingly able mirrorless cameras just helps support the size and weight advantages that 70-200mm equivalents offer over actual 70-200s. So if you're shooting APS-C, it might be worth asking yourself: which would really be more useful to me?