Don't Get Hung Up on Lens Zoom Factors

I see a lot of posts and comments about focal length, in particular zoom ratios of lenses (also called the zoom factor). With a number of recent wide angle lenses (e.g. 11-16mm f/2.8 APS/DX), sometimes these comments get really out of whack with reality. Someone recently commented about some of these wide angle primes with the words “what is there, a contest to make the lens with least amount of usable focal length range?” That person is showing their ignorance. Indeed, one wonders whether they would ever shoot with any prime, which is, after all, a zoom lens with a zoom factor of 1. 

It doesn’t help that the camera makers have long been in a game of X wars. As in 4x, 10x, and now with the Coolpix P900, 83x optical zoom! I put the exclamation point there as I’m starting to see product marketing with an exclamation point after the optical zoom range. 

But focal length isn’t truly a revealing statistic. A 2x zoom at wide angle can be quite different than a 2x zoom at telephoto in the variability of imagery you can create with it. 

Let’s look at a chart for a moment (I’ll use the one that’s been on my site since the beginning). The truly important thing to pay attention to here is angle of view:

Angle of View
35mm (FE) APS (E, NX, XF) m4/3 CX (Nikon 1)
104 degrees 14mm
10mm* 7mm 5mm*
84 degrees 20mm 14mm 10mm 7.5mm
74 degrees 24mm 16mm 12mm 9mm*
65 degrees 28mm 18mm 14mm 10mm
54 degrees 35mm 24mm 17mm 13mm
40 degrees 50mm 35mm 25mm 19mm
29 degrees 70mm 50mm 35mm 26mm
24 degrees 85mm 60mm 42mm 31mm
19 degrees 105mm 70mm 50mm 39mm
10 degrees 200mm 135mm 100mm 74mm
7 degrees 300mm 200mm 150mm 110mm
5 degrees 400mm 270mm 200mm 150mm
4 degrees 500mm 335mm 250mm 185mm
3.5 degrees 600mm 400mm 300mm 220mm

One of the most restrictive of the current wide angle zooms is the 11-16mm f/2.8 APS/DX (another is the upcoming 14-20mm f/2 for APS/DX cameras). Neither even reach a zoom factor of 2x (pity the poor marketing team having to deal with that! ;~). But that 14-20mm on the crop sensor body it’s intended for gives you angle of view differences of over 20 degrees. That’s a pretty significant differential. But just as important is the perspective change. If I frame a person fully at 14mm I’m at about 3.5 feet . If I frame that same person fully at 20mm I’m closer to 5 feet. My perspective is changing fairly considerably.

One of the dangers in dismissing zoom lenses with modest zoom ratios is that you’re essentially saying “it doesn’t replace enough prime lenses.” But is that true? Actually, that 14-20mm f/2 replaces three prime Nikkors: the 14mm f/2.8, the 18mm f/2.8, and the 20mm f/1.8 (or f/2.8) (if you want to think in FX terms, that's more like replacing a 20mm, 24mm, and 28mm lens). Sure, the Coolpix P900 replaces more than a dozen prime lenses, but realistically, how many primes do some other common zooms replace? For example, the 24-70mm: four, best case (24mm, 35mm, 50mm, 70mm, though this latter isn’t a Nikkor prime offering). Heck, how about the 18-140mm DX? Only seven (28mm, 35mm, 50mm, 85mm, 105mm, 135mm, 180/200mm). That’s a super zoom, and it truly only replaces seven prime lenses in your kit.

So why the complaints about only replacing three? Because the posters are paying attention to the wrong number, basically. Moreover, when you zoom only a little bit you’re keeping perspective fixed and changing your cropping slightly. Most of these complaints about lack of zoom ratio are convenience complaints from people not controlling all photographic variables in traditional ways.  Moreover, they may not be using tools that are already available to them. 

For example, let’s say I’m off in Africa with my D810 and  500mm lens. Would I rather that it was a 500-750mm zoom so I can handle crops when I can’t quite get as close to an animal as I want? Funny thing is, that combo actually is a 500-750mm zoom. Say what? 500mm at FX, 600mm equivalent at 1.2x image area crop, 750mm equivalent at 1.5x image area crop. I’ve got Image Area Crop set to my function button so that’s almost as convenient as a zoom ring, I’m just using my right hand instead of my left. 

But wait, I’m losing pixels. Well, that’s the great thing about the D810, and one of the reasons why I’ve consistently called it the best all-around DSLR available during its reign as Nikon’s highest resolution body: I’ve got 36mp at FX (500mm), 24mp at 1.2x (600mm), 15mp at 1.5x/DX (750mm). I’ll remind people that prior to the D800 coming out in 2012, my best body was 24mp and most of my wildlife images were actually 12mp. 

So don’t get overly hung up on zoom factor numbers. Look instead what a lens is actually going to do for you in practice. In practice, virtually every wide angle lens zoom currently made (10-24mm, 11-16mm, 14-20mm, 14-24mm, 16-35mm, etc.) is replacing three or more of the prime lenses I would have carried without the zoom. My only issue is with whether I’m losing too much image quality with the zoom construction compared to the prime, not the size of the zoom factor.

Since I know someone will ask, the reason why the 11-16mm is in my DX kit and the 14-24mm is in my FX kit is very simple: both those lenses replace three primes for me, just different ones. I don’t feel I’m actually sacrificing anything in terms of optical quality, either. Indeed, both of those lenses are in my opinion better optically than the Nikkor 14mm f/2.8 and 18mm f/2.8, two of the lenses I'm duplicating.

text and images © 2017 Thom Hogan
portions Copyright 1999-2016 Thom Hogan-- All Rights Reserved
Follow us on Twitter: @bythom, hashtags #bythom, #dslrbodies