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Telephoto

As is to be expected whenever Apple announces something new, a lot of shit is being flung around in the tech sphere over the iPhone 7 and 7 Plus. One particularly fun nugget is that the secondary camera lens on the 7 Plus’s dual-camera system is not, despite what Apple says, a telephoto lens. This is based on a few mixed-up notions from people who know just enough about photography to think they know a lot: namely that ‘telephoto’ is synonymous with ‘long’, and that 56mm (135 equivalence, when will this die) is ‘normal’ (and therefore not ‘long’ ‘telephoto’). 50mm was standardized on the 135 format because Oskar Barnack said so, essentially. Different versions of the story say that the 50 was based on a known cine lens design, or that glass to make the 50 was readily available, or that it was necessary to fill the new large image circle, but whatever the original motivating factor was – the original Leica I set a new standard with the 135 film format, and a new standard somewhat-longer-than-normal focal length with its Elmar 50/3.5. The idea behind normalcy is matching our eyesight. This, conveniently, tends to match up with the length of the diagonal of the imaging plane; √(24²+36²)≅43mm. 50 is already noticeably longer than this, and 56 even more so. There’s a reason 55-60mm lenses were popular as more portrait-capable ‘normals’.

Photographers do typically accept that lenses in this range are normal for 135, yet you rarely saw such a concession on other film plane sizes of the time. Nowadays, with digital APS-C formats demanding new lens lineups, both the long-normals and true-normals seem alive and well. But none of this really matters much when a print from a 135 fitted with a 55 (I don’t know of any 56mm 135 lenses, but I’ve used plenty of 55s) is slightly-but-still-noticeably longer than our normal field of view. I wouldn’t be surprised if the focal length decision was at least partially based on technical desires for the depth-mapping system. Regardless of the reason, however, it’s a great choice. It’s a great choice because it’s not normal. It works in situations where a normal lens is desired, but gives just a little something extra to portraiture — which is a big selling point of this camera. A little added drama, slightly flattened perspective, and (potentially irrelevant on the iPhone, but generally speaking) just a touch shallower depth-of-field.

Beyond this, however, it’s worth noting that Apple doesn’t call it a long lens, they call it a telephoto lens. This is a description of the optical design, not the focal length. Telephoto lenses are associated with big beefy long lenses for a good reason: focal length is directly related to the point where all the light coming in converges before spreading back apart to hit the sensor. In a simple optical design, this means physical lens size increases proportionately with focal length. Telephoto designs use optics to move this point around, so the center is no longer dictated by the center of the housing.1 This is great when you don’t want your 200mm lens hanging a foot off your 135 SLR, but I can also imagine such a design would come in handy even at moderate focal lengths in such a compact package. If the promotional artwork on Apple’s site is to be believed (which I doubt, but let’s go with it), the wide lens is more recessed than the telephoto, but not by much. It seems entirely plausible that Apple is, in fact, using a telephoto design for this lens. It also seems perfectly likely that they aren’t, but nobody has torn down the optical construction yet to determine this.

Maybe the lens isn’t a telephoto. It’s definitely long, though not extreme. In the end, it doesn’t really matter – it’s a great choice for a secondary focal length anyway. It will certainly be a boon for portraiture, which seems to be a major focus for Apple with this release. I’ve just seen so much half-information thrown out in semantic criticisms of Apple in the past couple of days, with nothing to back it up beyond half-baked notions of what it means to be ‘telephoto’.


  1. Oddly enough, the same casual conflation hasn’t occurred with wide lenses. We always call these wide, even though many of these only exist because of special (retrofocal) optical designs as well. The design of an SLR requires a large gap between the back of the lens and the imaging plane (for the mirror); simple wide angle designs would protrude into this space, so optical designers construct SLR wides such that their effective focal length is farther forward than the physical center. ↩︎