The keen observer will notice a discrepancy in the actual sensor size and the “categorized” sensor size of smaller sensors. Small sensors, like those in cell phones, will often be sized based on a fraction-of-an-inch standard. The iPhone XS, for example, is a 5.6mm x 4.25mm Sony sensor (it’s active area is this size at least). But this is classed as a 1/2″ sensor. Now on these smaller sizes, the measurement is diagonal, unlike the width measurement of the 36mm film, but even so, the actual physical sensor size is much smaller than 1/2″. This is because this technology is based in old video sensor tubes which were measured in inches and not by their actual active image area. So to figure the actual crop factor of an iPhone relative to full frame, use the 5.6mm width figure for an approximate 6.4x crop factor. This means the 4.2mm focal length wide angle lens of the iPhone XS is between 26–27mm.
These two formulas are more advanced than we will cover here, but they come in useful: Field of View to Focal Length
ANGLE OF VIEW (IN DEGREES) = 2 ARCTAN( SENSOR WIDTH / (2 X FOCAL LENGTH)) * (180/Π)
There are other sensor sizes as well. The popular Micro Four Thirds cameras use an even smaller sensor (close to a 2X crop of full frame). Other high quality cameras use a 1” sensor, like the popular Sony RX100 series or the DJI Mavic 2 Pro drones. Many cell phones in 2019, center around a 1/2” sensor. Going the other direction, there are medium and large format stills cameras with sensors as large as 9×11” (This would be consider “Ultra Large Format” and isn’t really practical in 2019). On the motion picture side there’s IMAX. IMAX film is not only 65mm wide (much larger than the aforementioned 35mm), but it’s run horizontally through the camera like the stills cameras do. Each frame occupies 15 perforations meaning the film has to move at over 6km/h through the camera. This makes for an imaging area 9 times larger than that original 35mm format, at the cost of extreme bulk, noise, and a high price. The world of IMAX cinematographers is not large and I’ve had the privilege of working with some of the few cinematographers and directors who still shoot this format. There’s a reason they love it so much, but it’s not a practical solution for most shoots. So what’s the digital equivalent to IMAX? Well, it’s been slow to come, but you may have seen the first Hollywood film to be shot entirely in digital IMAX if you witnessed the micro budget, independent film “Avengers: Endgame”. ARRI Alexa IMAX digital camera (2015) Avengers: Endgame was shot completely with this camera. That being said, Vision Research also made a 65mm camera which you likely never heard of so this really isn’t a new idea. And, even the IMAX-labelled Arri is a 65mm camera, so in terms of surface area of its sensor it’s drastically smaller than its IMAX film counterpart. So remember how we talked about lens and sensor sizing working in tandem. Not only are cameras like this rental-only items, the lenses are rebranded Hasselblads designed to cover medium format size. And you can’t afford either of them. But the good thing is, you don’t need to. And you don’t need to care about the information presented in the latter half of this video for anything more than information’s sake. If you consider what the high-end cinema industry has gone to to get to this level, and that the majority of your favorite films have likely been shot on that traditional super-35 or APS crop sensor size, isn’t it a marvel to thing what you can do with a full frame A7 series Sony camera? In my view, IMAX as a format is little more than a brand labeling that has little to do with an audience’s experience when watching a film. If resolution and size were the most important factors, there likely would have been more public outcry over the “LieMAX” maneuver when IMAX replaced their high resolution film projectors with 2K “low resolution” equivalents. Nobody I know personally cared much, and many still paid the additional premium for a regrettably inferior technical experience. If they cared about this during the movie though I doubt the movie was well made.
Steve Yedlin’s resolution demo is a very insightful look at comparing the resolution of several of these larger formats, both in film and digital varieties: http://www.yedlin.net/ResDemo/ResDemoPt1.html