What Point & Shoot Would I Buy?
January 26, 2010
Even as I try to warn people away from high-megapixel point & shoots, some commenters have despaired that my advice isn’t very practical: Virtually every model sold today is 10 Mp or higher.
There’s a reason the last “sensible” point & shoot, the beloved Fujifilm F30/F31, actually went up in price after being discontinued. And even three years later, a used one can change hands for over $200. This despite the fact that aside from the superior 6 Mp sensor, the F30/F31 models were otherwise totally ordinary.
But all of us do need small, take-everywhere pocket cameras. Your cell phone cam can only do so much, with its grainy images and lack of controls.
So what specs would a point & shoot need to have, before I could recommend it? Well, here’s some thoughts—or perhaps just a poignant yearning for the impossible.
The recent Canon S90 proves it’s physically possible to put an f/2.0 lens and a 1/1.7″ sensor into a pocket-sized camera. It’s not quite as slim as Canon’s old Elphs. But it’s still smaller than the venerable 1979 Olympus XA, the breakthrough model which first showed the world how fine a shirt-pocket camera could be.
The S90 includes All Mod Cons: A jumbo 461,100-dot LCD; face detection; RAW option; and a movie mode (though not in HD, weirdly).
The so-called 1/1.7″ sensor size is actually 7.6 x 5.7 mm. The S90’s pixel density of 23 Mp/sq. cm means each pixel is about 2.1 microns wide.
Canon gets credit for scaling back the megapixel count in some recent cameras, compared to earlier models (the S90 is 10 Mp). But to my thinking, diffraction and noise still make 2.1 micron pixels pretty borderline. But is that a problem for the image quality, really?
Well, DPReview hasn’t tested the S90 yet. However its big sister, the Canon G11, recently got the full DP Review workup. And since both cameras apparently share the same sensor and Digic 4 processor chip, the results should be similar.
Unfortunately when you look at the tests at different ISOs (scroll down to the green feathers), you see that by ISO 800, the noise-suppressing algorithm is also blurring away lots of fine detail. And Canon is actually overstating its “800” speed slightly—in reality it’s closer to 640.
For our daily snapshots we rarely need a bazillion megapixels, not for any real-world use. You can make crisp 8×10″ prints, or get a nice magnified view on your computer, with only 6 Mp. (And even then, you’d still be ahead of James Cameron!)
Let’s say you took the chip dimensions of the S90, but held it down to 2828 x 2121 pixels (6 Mp total). Each pixel would be 2.7 microns wide—65% more area than those in the S90. That’s a significant difference. High ISOs wouldn’t need such aggressive anti-noise smoothing then.
But-but-but… Fewer pixels! Wouldn’t you lose detail doing that? No—at least not at any smaller lens opening than f/4.5. By that point, diffraction blur is much larger than 2.1-micron pixels.
Could we also hope that dropping to 6 Mp would also knock some bucks off the S90’s $400 price? That’s awfully steep, considering how inexpensive an entry-level DSLR is today.
Okay, here’s my next crackpot request: No zoom lens.
I realize from a marketing point of view, this sounds insane. Isn’t a 4x zoom better than a 3x zoom, and a 12x zoom best of all?
The problem with a zoom is, as jack-of-all-trades, it is master of none. A zoom is inevitably larger than a single-focal-length lens, and not always as sharp.
But the biggest problem is that zooms cripple the maximum aperture. For many typical ones, f/3.5 is the brightest f/stop. (Yes, they might be a little better at the widest zoom setting. But when a lens is labeled something like f=8–24, 1:2.8–5.9, the latter numbers tell how the the widest f/stop dims as you zoom in.)
You can make a single-focal-length lens (often known as a “prime”) much faster. Like two stops brighter. I think a smart marketer might get some mileage out of the promise, “gather four times as much light!”
A small image format actually makes it easier to design a fast lens, compared to e.g., one for DSLRs. If you look into closed-circuit television cameras, you’ll discover oodles of f/1.4 or even f/1.2 lenses that cost less than 90 bucks.
If you compare how much sharper a point & shoot image looks at ISO 200 versus 800, it raises an interesting thought. Your extra two stops of lens brightness might let you crop the image quite a bit harder, while still getting adequate detail. In effect, you could “zoom” after the fact, at home on the computer.
A wide maximum f/stop would also let you throw backgrounds a bit out of focus, if desired—a tool creative photographers appreciate. (Admittedly, any DSLR will be better at this.)
And lenses starting from f/1.7 would permit a greater range of possible apertures, before you hit the diffraction limit (about f/5.6 or smaller, with 2.7 µm pixels) and begin to lose sharpness.
But I admit, the no-zoom option is probably something grandma wouldn’t go for.
So that can be the special “Petavoxel” edition. And believe me, I’d pay for it.