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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  • strikeback03 - Tuesday, July 06, 2010 - link

    How does international work? Are other parts of Europe covered by that as well or are they all additional? Reply
  • B3an - Thursday, July 01, 2010 - link

    Theres way WAY less options for network and internet providers in the U.S, especially compared to here in the U.K..
    So less competition means higher prices. And of course the size of the U.S/Canada is a problem.
    Reply
  • strikeback03 - Thursday, July 01, 2010 - link

    Some friends who have been living in England say that cell usage over there is way more expensive. They claim the only affordable way to do it is with pay as you go SIMs and just not use them much.

    But yes more competition would be nice. For me Verizon is the only carrier that offers the kind of coverage I need. So between the fact that I can't go anywhere and that they don't offer an off-contract rate I have no reason not to take the subsidized phones and contract extensions.
    Reply
  • Chissel - Sunday, July 04, 2010 - link

    I'm an American living in the UK. iPhone 4 rates here are much lower. The best I have seen is from Tesco (o2 network). Low cost no frills service. 750 minutes + unlimited texts + 1gb of data per month. Also, incoming calls do not charge minutes. 1 yr. contract 32gb iPhone 4 = £299/$450 + £35/$50 per month (all tax included). After 1 yr. they have to unlock your phone. After you unlock the phone you can drop down to £20/$30 per month.

    This means the 2 year cost of the phone + service in the UK is £959/$1,438. In the US the 2 year cost is $299 + tax and $105/mo + tax. Total cost over 2 years is $2,819 without tax.

    As you can see the UK has much lower price over the 2 years. Plus, after 1 year you 'own' your phone and can resell and buy iPhone 5.
    Reply
  • strikeback03 - Tuesday, July 06, 2010 - link

    I think the unlock on AT&T can be requested after 3 months, definitely after a year as I had a friend do that. Reply
  • StormyParis - Saturday, July 03, 2010 - link

    I've abandonned data plans, and switched back to plain voice, on my HD2. I get Wifi most everywhere (at home and at work for sure, and most places in between). I was simply not using data that much, it's not worth the monthly 30 euros they want for it.

    99.5% of the time, there's no difference at all. 0.5% of the time... i can survive...
    Reply
  • vol7ron - Wednesday, June 30, 2010 - link

    I agree, but...

    "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. The latter is a message we've seen a few times before with OS X issues..."

    Apple would just see this as another selling point for the bumper.

    Anand/Brian-
    I'm curious if you've had a chance to test with the microfilm covers like Bodyguardz or Zagg.

    I use these because of how thin they are and how great they are at protecting the device (scratch free even when dropping on concrete). They cover all points of the phone rather effectively. I'm curious if they would be beneficial to your testing.

    vol7ron
    Reply
  • Brian Klug - Wednesday, June 30, 2010 - link

    vol7ron,

    You're totally right, I need to test with a thin film or some heavy duty tape/invisible shield. I originally thought of doing that, but somehow it got lost in all that frenzied testing. I'll whip something up and see if anything changes. I mean that's a good point too, it might not do very much.

    I mean, ultimately there's a thickness you do need to achieve, and to be fair a lot of the benefit the case adds is that extra couple mm or two from the antenna. If the film is too thin, it might not do much. What makes me uneasy about saying anything definitively is that this is so near field - literally on top of the radiative surface. I'll admit I have only a basic level of understanding about what kind of interference happens in the very near field. I mean even at 1.8 GHz, one wavelength is 16 cm - the case and your hands on the phone is way inside near field.

    -Brian
    Reply
  • rainydays - Wednesday, June 30, 2010 - link

    Agree. Outstanding review. The detailed analysis and level headed tone is excellent. Keep up the great work.

    Antenna section was illuminating. Good point about using SNR. I wonder if that number by itself is sufficient though. I guess signal power in dbm along with SNR would give the most complete picture of reception.

    At any rate, as is abundantly clear in the article, you never really know where you are till you see the numbers.
    Reply
  • John Sawyer - Thursday, July 01, 2010 - link

    Yes, the numbers, details, etc. are more important than a lot of people realize. It often annoys me when I see people commenting about issues that involve actual measurement, technical facts, etc., without referring to any of those, and thus winding up with all kinds of conspiracy theories, bogus suggestions, etc. As applied to hardware problems from any manufacturer, generally many such commenters, in their understandable desire to just see a fix for a problem, wind up suggesting the only important thing is for the manufacturer to set up a return exchange program, which would be nice if it were always that easy, but it doesn't address the details of the problem that are often quite interesting, and can be very useful for people trying to learn from the situation. Reply

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