Every time somebody bumps up the number of megapixels, there's always another set of blog posts about how useless the megapixel race is. But I don't think they get it right all the time.
It helps if you invent some words to describe the universe. So I'm going to make up a term called a "bogo-megapixel". It's an imaginary number that you can apply to any combination of camera, digital sensor or film, and camera and has nothing to do with the real number of megapixels you see.
If I take two twelve megapixel cameras... say a Canon G9 and a Canon 5D... I will find that the 5D has significantly more bogo-megapixels than the G9, even though the number of megapixels are the same.
But I'm not actually going to give you a real numerical definition, because then you'll try to see that it's a number to compare cameras on and make up a chart. Which it can't, because you may think a camera has 10 bogo-megapixels and I may think it's 4 bogo-megapixels and we could both be right because our priorities are different.
There's a common meme that there's some magical number of megapixels that is the most you'd ever want. Maybe it's four or six or ten or something.
This is hogwash. If there's a gigapixel digital camera on the market, people will buy it and find something fun to do with it. Like the Casio EX-F1.
Also remember that the size limit of an ink jet printer is primarily for marketing and desk space. Higher end people want bigger printers and will pay more. The added cost of lengthening the track the head moves on and extra plastic is fairly negligible. If we all had gigapixel cameras, we'd all want huge ink jets and we'd do silly things like covering a wall with a single snapshot.
The big thing to remember is that this is somewhat dependent upon subject matter... which is really where the cognitive dissonance starts. For people and vacation snappyshots and things like that, you probably don't need the resolution. For portraits, you may blur out any fine detail because nobody wants to look at pores. People don't tend to walk right up to a print of a portrait and try to see how good the fine detail is any more than they like to take a magnifying glass to people. But for scenery, there's always more detail to be had if you get in. Can you see the ants on the tree? Can you see the cow in the far distance?
This is why one person can take a 4 megapixel shot and blow it up huge and be quite happy with it and another person needs a 39 megapixel digital back to be happy at the same size. Either way, I've got tons of shots taken on gear that's not as high resolution as my medium format film camera, and so it's going to bug me forever that I won't be able to make them as blown up as the ones I've got.
But there's a bigger problem than having the right number of megapixels.
So, back to bogo-megapixels. If you realize that the bogo-megapixel is an imaginary number used to represent the total performance, you start to understand that as you increase the camera's ISO setting to collect more light, you are really just trading bogo-megapixels for faster shutter speeds
So, for compact cameras, what's really happening is that the number of megapixels keeps going up, but the number of bogo-megapixels is about the same. This is why so many of us are disgusted. We recognize that if we'd have the number of bogo-megapixels at about the same level as the number of real megapixels, we'd fit more pictures in the same memory card, we'd be able to shoot at a slightly higher ISO, and the camera would be faster because it would be slinging less data around.
Now, what about SLR cameras?
We've crossed a barrier recently, where the latest crop-factor digital SLR cameras have sensors smaller than 4 megapixel per square centimeter. The EOS 50D is currently the first on the race to the bottom, with four and a half megapixels per square centimeter.
There are some fairly hard limits that have been able to be pushed off with careful design. Sensor makers have spent a lot of time making better microlenses and increasing the fill factor and other advances, which means that newer generation sensors at the same level of resolution can collect more light and have less noise than before.
But we're also seeing manufacturers trying to avoid basic fundamental limits by cheating. You can run noise reduction algorithms on the image and make some of the noise appear to go away. It'll even make your pictures of a gray card look clean. But if you start photographing real objects, you'll realize that fine detail that the software can't tell apart from noise has been smeared together.
Just out of curiosity, I went back and looked up what sensors were like back when you didn't shudder to view things at 100% when they came out of a point and shoot camera. Remember, my A95 has about the same number of bogo-megapixels as my G7, even though the A95 has 5 megapixels and my G7 has 10. Reviews of the A95 pointed out that the follow-on to the A95 had better have a bigger sensor, maybe a 2/3rds sensor, if they wanted to bump up the resolution because it was starting to get some comments about objectionable noise and a tiny dynamic range. And that's about 13 megapixels per square centimeter. So we haven't hit the point where the bogo-megapixels can't go up without making the sensor bigger, at least in terms of ISO 50-100 performance.
I'm repeating myself here, but, as far as I'm concerned, I'd actually be fairly happy with a digital SLR that has maybe 20 megapixels and an APS-C lens because I'd leave it set at ISO 50 or 100 and probably pair it with a tilt-shift lens and carefully consider diffraction and depth of field concerns while shooting and be able to print crisp 20x30s. Assuming you can peel my film gear out of my hands, of course. And I can guarantee that your average shooter is not going to be able to respect or understand diffraction limits well enough to actually get the necessary resolution out of it.
So, while in the SLR form factor, the bogo-megapixels have, so far, been increasing at about the same as the number of megapixels and most cameras retain an impressive number of bogo-megapixels even at high ISOs, this is likely to come to an end. The problem is that binning and blurring are incomplete solutions to this sort of problem. You lose more bogo-megapixels faking things than doing it right while laying out the sensor.
So, this is what the real problem is. We want it all but we can't have it all. The majority of shooters probably will be happier with better high ISO performance than with having more megapixels. Did you realize that if you take a 6 megapixel APS-C sensor, it's about the same pixel pitch as the Nikon D3 that is famously crisp at most ISO settings below 3200? So, while I'd probably like a 20 megapixel APS-C sensor, the vast majority of casual shooters would prefer a 6 megapixel APS-C sensor that went up to ISO 25,600.
You want to know what I really think? I bet the Canon 50D's claims of getting one and a half more stops because of improved microlenses and noise reduction is about as credible as getting forty more horsepower in my car with a new air filter and an exhaust tip.
I think I've already done the last model shoot in the current place... Everything's all a mess as we get things packed and ready to go ahead of time.