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
POST A COMMENT

201 Comments

View All Comments

  • dacramer - Tuesday, November 01, 2011 - link

    The browser benchmarks show the 4s as fastest, but this benchmark is FLAWED as a measurement of CPU performance.

    The benchmark compares Safari to the Android stock browser. The stock Android browser does not support 2 cores, only 1. So all Android dual cores phones would be nearly twice as fast with another browser such as Opera.

    I'm surprised Anand did not include this discussion in the review. He seams fixated on the idea that stock to stock browser is a valuable comparison when it totally misleads readers on CPU performance.
    Reply
  • Lucian Armasu - Wednesday, November 02, 2011 - link

    In case you missed it, the Droid RAZR scored 10% faster than iPhone 4S in the SunSpider test.

    But yes, this is still mostly a software issue, and I expect the Android 4.0 browser to be even faster on the same chip.
    Reply
  • thunng8 - Wednesday, November 02, 2011 - link

    FYI, Google says the Galaxy Nexus scores 1983ms in Sunspider running ICS Reply
  • doobydoo - Wednesday, November 02, 2011 - link

    "Where did it show faster CPU?"

    Where did it in my comment?
    Reply
  • Breit - Thursday, November 03, 2011 - link

    I just run SunSpider 0.9.1 on my Galaxy S2, international model (everything stock, with Android 2.3.5) and it came in at 1626.5ms with Opera Mobile browser and 3354.8ms with the stock Android browser. So saying the CPU on the Galaxy S2 is weaker than the CPU on the 4S is just not right (and that by a big margin!).
    At least make comparisons with the best software there is and not just 'some' browser you eventually found on your phone...
    I'll bet there is someone programming his own browser just for the kicks or as an exercise for his programming skills and that browser scores over 9000ms in SunSpider. Does that mean the CPU in that phone is slow? ;)
    Reply
  • doobydoo - Friday, December 02, 2011 - link

    You could achieve the same results on the iPhone too..

    The comparison is (rightly) comparing stock browser to stock browser, and the iPhone 4S is faster. It would be even faster again using say, Opera.

    As for some guy posting 9000ms - you can filter the results to 'best' times so this is a non issue.
    Reply
  • Tetracycloide - Tuesday, November 01, 2011 - link

    Isn't there more to displays than just white level in nits, black level in nits (on a chart were I can't seem to find the Galaxy S II or the Infuse), and contrast (again, don't see the Samsung Galaxy S II or the Infuse on the contrast chart either)? Don't get me wrong, I don't agree in the slightest with the summary "this is apple cheerleading" but honestly the display comparisons are pretty lacking IMO. Where are the rest of them? There's more to a screen than just nits. Reply
  • medi01 - Thursday, November 03, 2011 - link

    Last time iphone disappeared from comparison photo, from the one where it would pale in comparison, when asked, author "explained' that he simply "forgot" it in the pocket. (!!!). Now they didn't even bother. Round of but kissing on "retina" hype and phones disappearing from charts.

    Find contrast of Galaxy phones on the charts pretty please...
    Reply
  • steven75 - Friday, November 11, 2011 - link

    Could you be any more of an Fandroid? Seriously. Reply
  • Stuka87 - Tuesday, November 01, 2011 - link

    Wait what?

    Almost every single page has a comparison to Android phones. Several of them have graphs showing the differences!

    And your comment on the displays may be your opinion, but actual measurements show otherwise. but hey, if you like your over saturated display with a much lower pixel density, thats your decision.
    Reply

Log in

Don't have an account? Sign up now