Welcome to 2010, Apple Upgrades its Camera

The iPhone 4 is equipped with two cameras: a 5 megapixel camera with LED flash on the back of the phone and a VGA camera with no flash on the front. The LED flash works in both still and video modes. Like the EVO 4G, the iPhone 4‘s flash allows you to shoot in perfect darkness. If you’re filming a video in low light the LED will stay illuminated while you’re recording.


Taken with the iPhone 4 in total darkness

The same unfortunately can’t be said for the front facing camera on the 4. In anything but good lighting you’re going to get noise. It’s really only useful for FaceTime (or as an alternative to a mirror) and even then you need to be well lit for it to look decent.

Apple has opted for a 5 megapixel OmniVision sensor for the rear camera on the iPhone 4. What's interesting is that Apple has decided to bring backside illumination front and center with their marketing.

Backside illumination improves the sensitivity of CMOS and CCD detectors by reducing the amount of material in the path of incident light. In a frontside illuminated detector, a considerable amount of light is lost due to absorption that doesn't result in emission of an electron, in addition to reflection off pixel structures and electrical components near the frontside surface. Backside illumination greatly improves sensitivity by flipping the stack over. Instead of light having to pass through and possibly be reflected by metal structures, it is converted into electrons and read out by passing solely through silicon. Creating a backside illuminated part isn't as simple as flipping a sensor over, however, as manufacturers also generally thin the silicon light has to pass through before it can reach the photodiode. This further improves sensitivity and is generally accomplished through chemical etching in acid or by lapping (physically grinding) sensors at wafer scale.


OmniVision OV5650 - iPhone 4's rear camera SoC

Though backside illumination (BSI) improves quantum efficiency (how many photons are converted into electons), backside illumination is hugely important for another serious reason as well. Because the sensor is small at 4.6 mm by 3.4 mm, pixel size is also extremely small at just 1.75 microns square for the OV5650 in the iPhone 4 (state of the art sensors are 1.4 microns square, like those in the HTC Incredible's 8 MP sensor). Frontside illuminated parts generally have in the neighborhood of 10-15 microns of silicon before the active region of the photodiode where one wants photons to get converted to electrons. The result is that without backside illumination, pixels have a 10:1 ratio of height to length, you can visualize them as looking something like long square pillars. But that's a problem.

As photons are converted into electrons in that silicon, there's no guarantee that it will immediately travel down into the gate structure below to be read out by the camera. Electrons drift as they descend these columns, meaning that photons incident on one pixel don't necessarily map to the gate below. Because the smartphone camera sensors are so small, with a 10:1 ratio of height to size, the result is large amounts of so-called quantum blurring from electrons traveling into the gate structures of adjacent pixels. The result is a blurry image (and a decrease in MTF at the sensor level!), thus not representing the image that used to be incident on the sensor.

OmniVision and other smartphone CMOS sensor manufacturers thin that column down in an effort to come closer to having the pixel look more like a cube than a huge pillar. Ballpark numbers are between 3 and 6 microns, down from 10-15. The result is much more sensitive sensors that are higher resolution. While megapixels don't necessarily matter, neither does pixel size as much anymore; it's all about quantum efficiency, which is what engineers really care about.


OmniVision BSI - Courtesy OmniVision

The optical system of the iPhone 4 is difficult to characterize without disassembly, though the focal length is a bit shorter than previous iPhones. The result is that the photos are demonstrably wider angle. Backside illumination also allows for a bigger chief ray angle, higher numerical aperture (and thus lower f/#), but I won't bore you with the details.

The Display in the Sun Camera Usability
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  • Griswold - Wednesday, June 30, 2010 - link

    Lets be honest, he has only very limited means to meassure the problem. To get to the bottom of this, it needs to be meassured in a HF lab. Reply
  • samspqr - Wednesday, June 30, 2010 - link

    "The fact that Apple didn't have the foresight to coat the stainless steel antenna band with even a fraction of an ounce worth of non-conductive material either tells us that Apple doesn't care or that it simply doesn't test thoroughly enough."

    I find it really funny that they would never catch this specific problem because of them just being apple: if their engineers are not as good as anand is (as in thinking "that's gonna be a problem" right after hearing the description of the antenna), and if THE FIELD TESTERS HAD THEIR PHONES DRESSED AS A 3GS BECAUSE OF PARANOID ISSUES, this kind of problem can only slip through
    Reply
  • The0ne - Wednesday, June 30, 2010 - link

    I think Anand was a little light on this topic. As an multi-discipline engineer myself this type of problem with the Antenna SHOULD NEVER had happened. It can only happened due to decisions that did not properly address it. This is not rocket science to engineers. If anything, testing WOULD HAVE discover the problem and yet it's in the finish product. Quite sad if you ask me.

    For example, why put a ferrite clamp on the end of the cable instead of designing it into the PCB . The only reason I can see why we did this was due to lack of time and we severely paid for it by having products become defective because the ferrite would pull the cables loose from the connectors.
    Reply
  • deppbv78 - Wednesday, June 30, 2010 - link

    I'm really disappointed at the lengths taken by AT to justify that iP4 losing signal as not a big deal...If it was any other product from any other manufacturer, I'm sure you'd not have gone to such lengths to justify the signal drop and just concluded that the phone has serious antenna problems. I'm not understanding why is it so difficult for anyone just provide an unbiased view of the product.

    I have HTC Hero & Touch Pro both of which lost a bar or two (with fluctuations) when cupped tightly. However, it was always just 1-2 bars and never went down like iPhone 4 does from 5 bars to 0. This continuous loss of signal is the problem. Justifying it telling that all phones lose signal is not right, as every other phone (including 3GS) loses signal temporarily and then stabilizes unlike iPhone 4.

    No wonder the iPhone 4 is engineering marvel, but that set aside it is also true that the design has created issues as well and the reviews need to acknowledge it and not justify it
    Reply
  • geniekid - Wednesday, June 30, 2010 - link

    HTC Incredible owner here. I think AT successfully showed that the antenna issue is NOT a big deal and their methods for doing so are sound. I share your suspicion that maybe they wouldn't have made such a significant investigation if it had been another phone, but let's not accuse them of mistakes they haven't made yet. Reply
  • bplewis24 - Wednesday, June 30, 2010 - link

    I have a sincere question though. Does this test really successfully show the antenna issue is NOT a big deal, or does it simply show that it's not a big deal in the utmost ideal conditions?

    Sometimes the article is difficult to decipher in terms of understanding who is saying what, but upon my initial reading I take it Brian did the testing of the antenna in Arizona. By his own admission (from my understanding), he lives there because the reception is absolutely stellar and about as good as it can possibly be.

    Again, from what I can tell, it is under those conditions that he conducted the attenuation signal loss comparisons. If it still drops down to 1 bar and comes reasonably close to dropping calls under the best possible conditions, how does it react under "average" conditions? Other people are reporting dropped calls for a reason. Is Brian's test the norm or an outlier?

    Please correct me if I've read this article wrong.

    Brandon
    Reply
  • anactoraaron - Wednesday, June 30, 2010 - link

    My understanding is you are partially correct in assuming (which is what I interpreted from your post) that under "normal" or "average" conditions you will go to one bar - which with the improved reception even at 1 bar you are still fine - OR will drop signal completely.

    This is also the reason why they say "At the bare minimum Apple should give away its bumper case with every iPhone 4 sold."

    Again, fantastic in-depth review.
    Reply
  • strikeback03 - Thursday, July 1, 2010 - link

    Well, he said the location he lives in has stellar reception. But he also said he drove around for a day testing, which implies to me that he found somewhere with a stable, "average" signal and did some testing there, then probably went somewhere with a "poor" signal and did some more, etc. Reply
  • bplewis24 - Friday, July 2, 2010 - link

    @strikeback03

    Correct. And in driving around to the less-than-stellar areas showed the phone dropping down below -107dB for reception when showing less than 2 bars. And this is on the low end of the reception spectrum as described earlier in the article. So it's pretty clear that the antenna does INDEED show poor signal strength in average or less than average areas when the "death grip" is applied.

    That is the determining factor. That determines that the design is defective and flawed. If it was not designed that way, when in average or below signal areas, the reception would still be average or below, and not well below because of the way you hold the phone.

    However, the article skirts this and attempts to present it in a way that shines the best possible light on Apple and their defective design. Big disappointment in terms of an objective review.

    Brandon
    Reply
  • geniekid - Wednesday, June 30, 2010 - link

    The article made it clear that bars are a misleading way of measuring call quality/reception. In practice, it was noted that call quality/reception is improved/equal to the 3GS on the 4, regardless of bars (raw signal power).

    Who cares if you have 1 bar all the time if you're still making calls better than someone with 4 bars?

    HTC Incredible owner here.
    Reply

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