Camera Improvements

Arguably the second largest hardware change (with the A5 SoC being the first and largest) in the 4S is the inclusion of a much improved 8MP camera. In case you’ve forgotten, the iPhone 4 previously included a 5 MP camera. Back when the 4 was introduced, Apple talked for the first time about backside illumination, and pixel sizes. In a later update, the camera got even better with the ability to buffer three full size images and merge to HDR in real time. This time, Apple brought up F/# and backside illumination again, and added one more thing.

Though Apple never talked about any of their optical design for the iPhone 4 camera, to the best of my knowledge the design likely was close to reference designs reported on a few lens lists consisting of four plastic elements. For the 4S, Apple has mixed things up by including its own optical design front and center, and made special note of a five plastic element design. I’ve put together a table showing the 4 and 4S in comparison based on what information is available.

Note that many have speculated that Apple is dual sourcing the CMOS sensor which seems likely, and given the sensors out there the two most likely choices are Omnivision’s OV8830 and Sony’s IMX105. Both of these have almost identical specifications, including 1.4µm pixels, a 1/3.2“ format, and an improved backside illumination process over the previous generation wafer-scale process. Omnivision’s BSI–2 process cites some specifications that seem to line up with what Apple talked about in their presentation, including better quantum efficiency (ability to convert photons into electrons), low-light sensitivity, and larger well capacity (which translates to increased dynamic range). You’ll note that the 4S uses the same sensor format as the previous generation - 1/3.2”, and includes more pixels, which results in the pixel size going down from 1.75µm to 1.4µm.

iPhone 4 vs. 4S Cameras
Property iPhone 4 iPhone 4S
CMOS Sensor OV5650 OV8830/IMX105
Sensor Format 1/3.2" (4.54 x 3.42 mm) 1/3.2" (4.54 x 3.42 mm)
Optical Elements 4 Plastic 5 Plastic
Pixel Size 1.75 µm 1.4 µm
Focal Length 3.85 mm 4.28 mm
Aperture F/2.8 F/2.4
Image Capture Size 2592 x 1936 (5 MP) 3264 x 2448 (8 MP)
Average File Size ~2.03 MB (AVG) ~2.77 MB (AVG)

Everybody likes talking about sensors (and I see lots of attention given to them), but any good photographer knows that it’s a combination of optical system and sensor that matters to performance. Optical design is important, and having studied as an optical engineer I find it interesting that Apple would draw attention to having a custom design of their very own with an additional plastic element. For a while I’ve held off on really talking about smartphone camera optics, but while we’re here, let’s touch briefly on them.

The iPhone 4S camera module

Thus far this generation and the one before it have primarily used 4 plastic elements, and virtually everyone but Nokia uses nothing but plastic (Nokia famously uses Zeiss-branded designs, often with glass elements). Optical design is generally driven by material availability, and there are only a few optical grade (read: transmissive in the visible) thermoplastics out there - Styrene, Polystyrene, ZEONEX, PMMA (Acrylic) and so forth - the list is actually relatively short. Thankfully polystyrene and PMMA can be used to make something of an achromatic pair, with polystyrene as a flint, and PMMA as something of a crown. Plastic provides unique constraints as well though - coatings don’t stick well, not very many have great optical properties, they have a high coefficient of thermal expansion, high index variation with temperature (which oddly decreases with increasing temperature), and less heat resistance or durability among others. With all those downsides you might wonder why smartphone vendors use plastic, and that reason is simple - they’re cheap, but more importantly, they can be molded into complicated shapes. Those complicated shapes are aspheres, which are difficult to fabricate out of glass, and afford much finer control over aberrations using fewer elements, which is an absolute necessity when working with very little package depth.

Apple's 4S versus 4 infographic

So what does adding another element get you? Well, when you’ve faced with limited material choices, adding more surfaces gives you another opportunity to balance aberrations that start blowing up rapidly as you increase F/#. That said, there are tradeoffs as well to adding surfaces - more back reflections, increased cost, and a thicker system. In the keynote, Apple notes that sharpness is improved by 30% in their new 5 element design, and MTF is what they’re undoubtably alluding to.

Genius electronic optical - 5P lens. Compare to above.

Genius electronic optical has a page on their website with a lens system that seems likely to be what’s in the 4S, as the specifications include 8 MP resolution (same size), same sensor format, F/# (2.4), 5 plastic elements (5P) and looks basically like what’s in the 4S. Other than that, however, there’s not much more that I can say about this Apple specific design without destructively taking things apart. One thing is for certain however, and it’s that Apple is getting serious about camera performance, something that other handset vendors like HTC (with its F/2.2 systems) are also doing.

Apple made mention that it also included an IR filter in the 4S optical design. If you recall back to our Kinect story, I used the 4 camera to photograph the IR laser structured light projector that Kinect uses to build a 3D picture. The 4 no doubt has an IR filter (though not a great one), but it’s probably just a thin film rather than a discrete filter right before the sensor. The 4S includes what Apple has deemed a ‘hybrid IR filter’ right on top of the sensor, which is possibly just a combination of UV/IR CUT filter (UV is a problem too), and an anti-aliasing filter.

If you try and take the same Kinect (IR source) picture with the 4S, thankfully all those non-visible, IR wavelength photons get rejected by the filter. This doesn’t sound like much until you realize that silicon is transparent in the IR and will bounce around off the metal structures inside a CMOS or CCD and create lovely diffraction effects on fancy sensors. I digress though since that’s probably not what Apple was trying to combat here. On a larger scale, IR will generally just cause undesirably incorrect color representation, and thus people stick an IR filter either in the lens somewhere or before the sensor, which is what has been done in the 4S. The thin film IR filters that smartphones have used in the past also are largely to blame for some of the color nonuniformity and color spot (magenta/green circle) issues that people have started taking note of. With these thin film IR filters, rays incident on the filter at an angle (as we move across the field) change the frequency response of the filter and the result is that infamous circular color nonuniformity. I wager the other effect is some weird combination of vignetting and the microlens array on the CMOS, but when I saw Apple make note of their improved IR filter my thoughts immediately raced to this ‘hybrid IR filter’ as being their logical cure for the infamous green circle the iPhone 4 exhibits.

Another minor difference on the 4S is that the LED flash is improved. The previous LED flash had a distinctively yellow-green hue, the LED flash on the 4S seems slightly brighter and also has a temperature that’s subjectively much closer to daylight, though I didn’t measure it directly. I habitually avoided using LED illumination on the 4 and will probably continue to do so on the 4S (and use HDR instead), but it does bear noting that the LED characteristics are improved. Unfortunately the diffuser and illumination pattern still isn’t very uniform or wide. It also seems that all this talk of moving the LED flash to the other side of the device to combat red eye turned out wrong as well.

Display Improved ISP in A5


View All Comments

  • Pata - Tuesday, November 1, 2011 - link

    Will these factors (bluetooth and gps) be incorporated in future tests? I now keep bluetooth and the gps on for Siri and geofenced reminders. I'm guessing that Android phone users might be soon be using bluetooth more often as well, given all the bluetooth watch accessories that will soon be available for their platform. With bluetooth and gps left on, with find my friends, reminders all running in the background, my iPhone usually doesn't last anywhere up to 9 hrs of usage. Reply
  • DukeN - Tuesday, November 1, 2011 - link

    Thanks Anand for reviewing every single Apple, iOS, Android/Droid major and minor update since the summer. How about we perhaps devote 2 frickin pages to cover/preview/benchmark some of the newest Blackberry devices?

    Heck you even covered turds like the HP Veer, and Windows Phone devices.

    Perhaps we can devote a couple of pages to the smartphones that have a quarter of the market?

  • jamyryals - Tuesday, November 1, 2011 - link

    Even as a [forced] Blackberry user, I'd rather they didn't spend their time reviewing Blackberry devices.

    Also, it is "biased" in that case.
  • SicMX - Tuesday, November 1, 2011 - link

    Fantastic review, keep up the good work!

    PS. Especially appreciated the in-depth review regarding the camera + image quality.
  • Matt Campbell - Tuesday, November 1, 2011 - link

    Nice article Brian, Anand. One clarification for Page 8, Siri can't read emails - only incoming (new) text messages. She'll tell you this herself if you ask her to read your emails :)

    And one comment, the addition of Bluetooth 4.0 is a big leap forward in my opinion. The Bluetooth stack in every other iPhone revision was missing the Serial Port Profile stack, which severely limited hardware developers. Since the 4S is "Bluetooth Smart Ready", it should support all kinds of fun new sensors and gadgets without the need for additional hardware.
  • _tangent - Tuesday, November 1, 2011 - link

    Great in depth review! Anandtech is one of the only places you can find this sort of analysis, and for the technically minded consumer, it's an invaluable resource. Kudos!

    I'm a bit confused by the GPU arms race in the mobile space. Aren't we reaching a point where the screen is small enough and far enough away from your face that the law of diminishing returns applies? Unless the ultimate objective is to have us all connect our phones to tvs or other displays for gaming on a larger scale.

    I'm not sure where i stand on mobile gaming these days. I have a relatively capable android handset, but find myself not even playing the 3D games already available. Not because they aren't good or pretty enough, just because intensive 3d gaming slams my battery, is less well suited to the odd 5 minute opportunity i get to game on the go, and the lack of physical controls for more "conventional" games is often frustrating. In any case, having lived with the handset for 6 months or so, i'm not clamoring for better 3D performance. Maybe plenty of people are though.

    I'm not personally a fan of Apple products. Not because they don't offer a great UX and aren't well polished in their own right, but because the cost apparently associated with that is too high. As a software developer by trade I find their draconian, fascist approach to the appstore and development in general somewhat distasteful. I don't equate choice and flexibility with complexity. That said, i don't mind Apple in a world where they have competitors offering an alternative philosophy This drives everyone to innovate which is great for us as consumers.

    Hopefully ICS will bring Android up to par with iOS from a UX point of view, whilst retaining the flexibility and customization that much of it's user base has come to appreciate. I look forward to a similarly comprehensive look at the Galaxy Nexus and other ICS phones as they're released!
  • Shinobi123 - Tuesday, November 1, 2011 - link

    Why is the New Razr missing from most of the graphs? It was in the first few, basically the only reason I kept reading this article.. But it wasn't included in any. :( Reply
  • tipoo - Tuesday, November 1, 2011 - link

    They probably aren't done testing it. Reply
  • rimshaker - Tuesday, November 1, 2011 - link

    As usual, the very best in depth product review available. As a EE, no review is ever thoroughly complete until I read it here on Anandtech. Wonderful!

    My only question is how to display the numerical wifi RSSI without using 3rd party apps? I tried it in field test mode but the wifi icon never changes like the cell signal does.
  • dubthedankest - Tuesday, November 1, 2011 - link

    I second this question as well as the one prior on how to enable the numerical RSSI for WiFi - that would be very helpful.

    Great review!

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