ou can actually check this for your phone if you have any photos on your PC. The real focal length will be recorded in the photo’s EXIF data. Typically, the maximum focal length of a normal smartphone lens is 6mm or less, simply because, even with a small “camera hump”, that’s all the room there is to work with.
More recently, some smartphones have added “periscope” cameras to their ever-growing array of cameras. These use a prism to redirect light to allow a longer lens with the sensor on its side. This, of course, also now limits the sensor width to about 6mm or less, but it’s a solution for telephoto lenses on a smartphone.
Last May I was offered the Honor Magic4 Pro for a review, and I’ve been playing with it ever since. This is a fairly typical setup for a premium 2022 smartphone: the main camera uses the largest sensor in the phone — the best quality — and will be using a pretty wide-angle lens. There’s probably an ultra-wide angle camera as well, and some kind of telephoto and/or portrait lens. The Magic4 Pro has a 3.5x telephoto, which mandated a periscope camera design. This is a 9.1mm thick phone, about 1mm thicker than an iPhone.
Here is an ultra-wide shot of the interior of my “he-shed” office here near the Delaware beaches. This is recorded as a 2mm lens, which is a 35mm equivalent of 13mm.
The other neat factoid about nearly all smartphone ultra-wide angle lenses is that they’re fisheye lenses. They’re not rectilinear. Sure, this looks pretty rectilinear in the shot, but what happens is that the camera app’s software de-fisheyes the fisheye. My pro cameras can do that, in-camera, and so can most photo editing tools.
They do that because the design of a very wide rectilinear lens is very complex. Nikon made an actual 13mm f/5.6 lens for full frame systems from 1976-1998. It weighs 1.22kg, contains 16 glass elements, and fetched around $33,000 the last time one was up for auction on eBay.
My Olympus M.Zuiko ED 8mm f/1.8 PRO fisheye lens, while not cheap, is relatively tiny and inexpensive by comparison. Okay, it’s got 17 lens elements, but they’re much smaller. The smartphone designers have to squeeze that into probably 6 or fewer lens elements, but they have some advantages. Nearly all smartphone lenses are made of molded optical plastic, which means they can create lens shapes not practical, or very expensive, in glass lenses. And they can also design around other flaws in a lens that can be corrected in software, targeting the design to just those elements — like controlling chromatic aberration — that are best to get right optically.
So, back to the Honor Magic4 Pro. Here’s a shot with the main camera, a 6mm lens which is reported in the EXIF data as being a 27mm lens in full-frame terms. However, I’ve noticed that the Honor camera app just slightly crops the image when shooting in normal PHOTO mode. This is pixel bucketing and cropping a 50 megapixel sensor to 12 megapixels, not 12.5, which is probably explains the difference. This is band playing on Bethany Beach, Delaware, part of the regular Thursday night summer free concert series.
Here’s a telephoto shot using the 3.5x sensor at its uncropped setting. This is really a 17mm lens, but has an effective focal length of 81mm based on the sensor size. An 81mm lens is a good focal length for portraits, but not quite what you need for this show.
The same camera can use some cropping and other software magic to give me the equivalent of a 479mm lens. However, it’s still just an 81mm-equivalent. They’re using the 64 megapixel sensor without pixel bucketing to deliver a better image, but it’s pretty clear that, while this is a fine shot for basic social media, you can see the image processing.