The Myth of the $500 FX Sensor

Bubble defects in a silicon wafer — SEM image
Bubble defects in a silicon wafer — SEM image

Disclaimer: I am not an electrical engineer and have no special knowledge about any of this.

Some time ago Thom Hogan estimated the cost of an FX camera sensor to be around $500 (I don’t have the reference, but I’m pretty sure this is true since he said as much recently in a comment thread). Similarly, E. J. Pelker, who is an electrical engineer, estimated an FX sensor to cost around $385 based on industry standard cost and defect rates in 2006. So it seems like there’s this general acceptance of the idea that an FX sensor costs more than 10x what a DX sensor costs (Pelker estimates $34 for a Canon APS sensor, which is slightly smaller than DX, and $385 for a 5D sensor).

My assumptions can be dramatically off but the result will be the same.

E.J. Pelker

I don’t mean to be mean to Pelker. It’s a great and very useful article — I just think it’s not that the assumptions he knows he’s making are off, it’s that he’s made tacit assumptions he doesn’t realize he’s made are completely and utterly wrong.

The assumption is that if you get an 80% yield making DX sensors then you’re get a 64% (80% squared) yield from FX sensors (let’s ignore the fact that you’ll get slightly fewer than half as many possible FX sensors from a wafer owing to fitting rectangles into circles).

Here are Peltzer’s “unknown unknowns”:

Sensors are fault-tolerant, CPUs aren’t

First, Peltzer assumes that a defect destroys a sensor. In fact if all the defect is doing is messing up a sensel then the camera company doesn’t care – it finds the bad sensel during QA, stores its location in firmware, and interpolates around it when capturing the image. How do we know? They tell us they do this. Whoa — you might say — I totally notice bad pixels on my HD monitors, I would totally notice bad pixels when I pixel peep my 36MP RAW files. Nope, you wouldn’t because the camera writes interpolated data into the RAW file and unless you shoot ridiculously detailed test charts and examine the images pixel by pixel or perform statistical analysis of large numbers of images you’ll never find the interpolated pixels. In any event (per the same linked article) camera sensors acquire more bad sensels as they age, and no-one seems to mind too much.

Sensor feature sizes are huge, so most “defects” won’t affect them

Next, Peltzer also assumes industry standard defect rates. But industry standard defect rates are for things like CPUs — which usually have very small features and cannot recover from even a single defect. The problem with this assumption is that the vast majority of a camera sensor comprises sensels and wires hooking them up. Each sensel in a 24MP FX sensor is roughly 4,000nm across, and the supporting wiring is maybe 500nm across, with 500nm spacing — which is over 17x the minimum feature size for 28nm process wafers. If you look at what a defect in a silicon wafer actually is, it’s a slight smearing of a circuit usually around the process size — if your feature size is 17x the process size, the defect rate will be vanishingly close to zero. So the only defects that affect a camera sensor will either be improbably huge or (more likely) in one of the areas with delicate supporting logic (i.e. a tiny proportion of any given camera sensor). If the supporting logic is similar in size to a CPU (which it isn’t) the yield rate will be more in line with CPUs (i.e. much higher).

This eliminates the whole diminishing yield argument (in fact, counter-intuitively, yield rates should be higher for larger sensors since their feature size is bigger and the proportion of the sensor given over to supporting logic is smaller).

(Note: there’s one issue here that I should mention. Defects are three dimensional, and the thickness of features is going to be constant. This may make yields of three dimensional wafers more problematic, e.g. BSI sensors. Thom Hogan recently suggested — I don’t know if he has inside information — that Sony’s new (i.e. BSI) FX sensors are turning out to have far lower yields — and thus far higher costs — than expected.)

Bottom Line

To sum up — an FX sensor would cost no more than slightly over double a DX sensor (defect rates are the same or lower, but you can fit slightly fewer than half as many sensors onto a die owing to geometry). So if a DX sensor costs $34, an FX sensor should cost no more than $70.

Like Thom Hogan, but for Canon

stadium seats in bryant-denny stadium
Stadium Seats in Bryant Denny Stadium (D5000, 18-200mm lens)

(Or “Like John Siracusa, but for Windows”.)

I was reading Thom Hogan’s latest piece on the state of the camera (from a Nikon shooter’s point of view) for 2010 and it occurred to me that I’d love to see a similar thing written from a Canon shooter’s point of view. I’m not the only one! As someone puts it in the linked thread:

As far as I know, there is no one very analogous to Thom Hogan, to talk about Canon as he does about Nikon. It’s sort of a Mac/PC situation, with Nikon in the Mac category, a brand that, because of its ikonic (sic) cultural appeal, attracts people to its brand in a way different manner than does Canon.

The rest of this post basically argues that Nikon (and Apple) users are delusional members of a cult who obsess about their favorite company, while Canon (and Windows) users just buy the best and cheapest product to get the job done and get on with their lives.

Thom Hogan (and to a lesser extent Ken Rockwell) is kind of the John Siracusa of the Nikon world, and just as there’s really no equivalent to John Siracusa in the Windows world, there’s no equivalent to Thom Hogan in the Canon world.

Consider the following negatives from Thom Hogan’s piece on the Nikon DX range:

  • Lack of consistent accessory connections (three different remote styles on four bodies).
  • Lack of consistent body style (D3100 is different from D5000 is different from D7000).
  • Lack of AI/AI-S support below D7000.
  • No in-body focus motors below D7000.
  • Strange feature inclusions/omissions to differentiate bodies.
  • Positionable LCD available on only one body.
  • Video still lagging, and no video enabled lenses in sight.
  • Constrast AF still lagging considerably compared to competition.
  • Quality control in Thailand plant seems to be strained, at best.

There’s not a single remark in the entire article defending Nikon or chiding Canon or whatever. This is a straight “Nikon is less than perfect and here’s why”.

And no, I can’t find a similar site discussing Canon.

So, what’s with the photo? I was looking for something I’d recently shot with my D5000 and I found it. (Rosanna and I had a “behind the scenes” tour of Bryant-Denny stadium during Dr. Robert Cialdini’s recent visit to UA.) I was going to caption it “a gathering of all the critical fans of Microsoft Windows and Canon DSLRs recently held in Alabama” but that would by petty.

Pentax K7

The next episode in the series “everyone except Nikon and Canon is doing interesting stuff” has come out. The newly announced Pentax K7 offers in-camera HDR imaging (by combining three photos), HD video (yawn), rotational vibration reduction, pro-level body construction in at an enthusiast price, pro-level viewfinder coverage (100%), and — zomg — an external microphone jack. It’s also smaller and better looking than its rivals.

And because it has in-body VR, its lenses are all cheaper. E.g. the 18-250mm lens is a little over $400.

It will be a shame if the street price isn’t considerably lower than the $1299 SRP. The street price on the model it replaces (the K20D, which is a very decent machine) is under $700.

Aside: at Adorama.com the Nikon D5000 is available now for around $730. The Canon T1i is around $800. The K20D is around $670 with those silly “add to cart to find out the price” deals, but it’s also out of stock, so it may actually be going out of production. Meanwhile the K7 is listing for $1300, the 50D is $1200, and the D90 is $975 (the D300 is $1700 … cough). If the K7 replaces the K20D with a price of around $900 it’s going to kick some serious butt (it would be $1350 bundled with an 18-250mm lens, which will probably be competitive with the Panasonic GH-1 with its 14-140mm lens, even when its price drops to reasonable levels).

One thing that may not be apparent from the picture above is how “lop-sided” the K7 is. Essentially the camera is really small (think smaller than an Olympus DSLR), but it makes up for this by having almost all of the body on the right side of the viewfinder. So, this camera essentially trumps everything on the market in features (except, aguably, the GH-1’s live view, and the flip-out LCD) while being metal, weather-sealed, small, having a pro-quality viewfinder (100% coverage, 0.95 magnification). And again, unlike Nikon and Canon, it’s not an intentionally crippled camera, so it has things like front and rear control dials, decent focus points, and a really good viewfinder. And, arguably, Pentax has the most interesting range of cropped frame lenses if you feel like spending money on cropped frame lenses which you’ll probably regret in a couple of years when everyone is shooting full frame again.

My only question is how fast and accurate the autofocus “feels”. (I have the same question about the GH-1.)

Panasonic announces prices for the GH-1

dpreview today links to Panasonic’s press release announcing pricing for the new GH-1. My reader will recall that I suggested this camera might give Nikon and Canon pause for thought — even if that thought is merely “hey, we need to start stealing ideas from Panasonic as well as Olympus”. Unfortunately, the announced price is $1499, bundled with a 14-140mm (effectively 28-280mm in 35mm terms) lens. This isn’t a terrible deal, but unless the street price is a lot lower, it’s not going to deter most punters from the “safe bet” of a Nikon D5000 or Canon T1i for ~$800, which will still be safely under $1499 with a Nikon or Canon 18-200mm lens (yes, Canon has one now in case you didn’t know).

It’s a safe bet that Panasonic has a lot of room to reduce the street price of the GH-1. Their excellent Lumix TZ cameras (of which I own two) tend to come in at the $350-450 mark and drop to the $200-250 range within a year. So, the $1499 may just be Panasonic’s plan for burning rewarding their early adopters.

D90x Approacheth?

With Canon’s new consumer DSLR offering 1080p video (albeit at 20fps), 15MP, and 14-bit RAW, the obvious shortcomings of the D90 are more obvious than ever. I also note that my favorite discount camera store is out of stock on the D80, while Amazon is selling D80s for the same price as D90s. Obvious conclusion — the D90 is replacing the D80 at the ~$700 price point and a successor to the D90 with the obvious deficiencies addressed is on its way.