I don't want a zoom lens on my phone

For cameras with swappable lenses, "prime" refers to any glass that doesn’t zoom. In general, prime lenses aren’t really understood by people that don’t buy expensive cameras; zoom was a standard feature on entry-level models long before digital cameras were a thing. But there are lots of reasons why enthusiasts often prefer primes, even when given the option. Primes can be really compact, for example. They usually allow for sharper images. And they can be designed with wider apertures, meaning better low-light performance and creative control over attractive blurry backgrounds. All of this is important for smartphone design, which involves cramming things into as small a space as possible. All things being equal, a prime will usually get you better image quality or a smaller lens. Often both.

Asus hasn’t given demos of its Zenfone Zoom at CES; the phone is only on show behind glass. But a look at the spec sheet reveals the compromises the company has had to make. Its 3x optical zoom lens starts with an aperture of f/2.7 at its widest angle, closing down to f/4.8 when zoomed in all the way. f/2.7 is already a little slow by smartphone standards — the iPhone 6 is f/2.2, for example — but the f/4.8 figure means the phone will capture around 150 percent less light at the long end, requiring longer shutter speeds to compensate. Don’t expect the Zenfone Zoom to be much use in dark situations — and that’s before we get into the likelihood of distortion, aberrations, and general sharpness issues that plague cheap zoom lenses. To say nothing of the gigantic bulge on the phone’s back.

But let’s say the technical limitations are surpassable — they probably aren’t any time soon, but for the sake of argument — even then, I’d still prefer a prime. To me, zoom lenses are for business, not pleasure. Primes force you to think about perspective and composition instead of using a zoom’s reach as a crutch. As often as not, zooms are a barrier between you and your photograph; just another thing to think about before pressing the shutter. The iPhone’s success as a camera owes at least as much to its speedy, reliable, predictable operation as its image quality.

I like taking pictures with prime lenses for the same reason I like taking pictures with my iPhone. I brought just one camera and lens with me to CES this week — Fujifilm’s X100T, which has a fixed 35mm-equivalent prime — because years of lugging excessive gear around have resulted in little more than back strain and missed photo opportunities while swapping optics. I’ve borrowed DSLRs to use for liveblogging press conferences, because that’s a situation that really does need a zoom lens, but it’s been a last resort. It’s that business versus pleasure thing.

Even with a prime lens, you still have ways to expand your shooting options. Fujifilm’s X100 cameras have wide and telephoto lens converters that don’t compromise on quality. This week, I’ve also been testing Olloclip’s upcoming 2x telephoto conversion lens for the iPhone 6, which is a pretty neat way to get a zoomed-in perspective. And the ubiquitous selfie stick is now the world’s most mainstream substitute for a wide-angle lens.

Still, if your phone is your only camera, I can see why you’d want it to zoom in theory. It’d help you get shots that just aren’t possible right now out of the box. But I’ve found myself taking pictures on my phone even when I have a far "better" camera around my neck, and its fixed lens is a big part of the reason why: it performs well and remains fun to use. Adding zoom at this point would compromise both.